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[PATCH 13/18] docs/system: put qemu-block-drivers body in an included fi
|
From: |
Paolo Bonzini |
|
Subject: |
[PATCH 13/18] docs/system: put qemu-block-drivers body in an included file |
|
Date: |
Wed, 26 Feb 2020 12:30:29 +0100 |
This removes the "only" directives, and lets us use the conventional
"DESCRIPTION" section in the manpage.
Signed-off-by: Paolo Bonzini <address@hidden>
---
docs/system/index.rst | 2 -
docs/system/qemu-block-drivers.rst | 987 +------------------------
docs/system/qemu-block-drivers.rst.inc | 954 ++++++++++++++++++++++++
3 files changed, 966 insertions(+), 977 deletions(-)
create mode 100644 docs/system/qemu-block-drivers.rst.inc
diff --git a/docs/system/index.rst b/docs/system/index.rst
index f66e6ea585..21b5a18b67 100644
--- a/docs/system/index.rst
+++ b/docs/system/index.rst
@@ -13,5 +13,3 @@ Contents:
.. toctree::
:maxdepth: 2
-
- qemu-block-drivers
diff --git a/docs/system/qemu-block-drivers.rst
b/docs/system/qemu-block-drivers.rst
index 388adbefbf..7ca890ea23 100644
--- a/docs/system/qemu-block-drivers.rst
+++ b/docs/system/qemu-block-drivers.rst
@@ -1,985 +1,22 @@
+:orphan:
+
QEMU block drivers reference
============================
.. |qemu_system| replace:: qemu-system-x86_64
-..
- We put the 'Synopsis' and 'See also' sections into the manpage, but not
- the HTML. This makes the HTML docs read better and means the ToC in
- the index has a more useful set of entries. Ideally, the section
- headings 'Disk image file formats' would be top-level headings for
- the HTML, but sub-headings of the conventional manpage 'Description'
- header for the manpage. Unfortunately, due to deficiencies in
- the Sphinx 'only' directive, this isn't possible: they must be headers
- at the same level as 'Synopsis' and 'See also', otherwise Sphinx's
- identification of which header underline style is which gets confused.
-
-.. only:: man
-
- Synopsis
- --------
-
- QEMU block driver reference manual
-
-Disk image file formats
------------------------
-
-QEMU supports many image file formats that can be used with VMs as well as with
-any of the tools (like ``qemu-img``). This includes the preferred formats
-raw and qcow2 as well as formats that are supported for compatibility with
-older QEMU versions or other hypervisors.
-
-Depending on the image format, different options can be passed to
-``qemu-img create`` and ``qemu-img convert`` using the ``-o`` option.
-This section describes each format and the options that are supported for it.
-
-.. program:: image-formats
-.. option:: raw
-
- Raw disk image format. This format has the advantage of
- being simple and easily exportable to all other emulators. If your
- file system supports *holes* (for example in ext2 or ext3 on
- Linux or NTFS on Windows), then only the written sectors will reserve
- space. Use ``qemu-img info`` to know the real size used by the
- image or ``ls -ls`` on Unix/Linux.
-
- Supported options:
-
- .. program:: raw
- .. option:: preallocation
-
- Preallocation mode (allowed values: ``off``, ``falloc``,
- ``full``). ``falloc`` mode preallocates space for image by
- calling ``posix_fallocate()``. ``full`` mode preallocates space
- for image by writing data to underlying storage. This data may or
- may not be zero, depending on the storage location.
-
-.. program:: image-formats
-.. option:: qcow2
-
- QEMU image format, the most versatile format. Use it to have smaller
- images (useful if your filesystem does not supports holes, for example
- on Windows), zlib based compression and support of multiple VM
- snapshots.
-
- Supported options:
-
- .. program:: qcow2
- .. option:: compat
-
- Determines the qcow2 version to use. ``compat=0.10`` uses the
- traditional image format that can be read by any QEMU since 0.10.
- ``compat=1.1`` enables image format extensions that only QEMU 1.1 and
- newer understand (this is the default). Amongst others, this includes
- zero clusters, which allow efficient copy-on-read for sparse images.
-
- .. option:: backing_file
-
- File name of a base image (see ``create`` subcommand)
-
- .. option:: backing_fmt
-
- Image format of the base image
-
- .. option:: encryption
-
- This option is deprecated and equivalent to ``encrypt.format=aes``
-
- .. option:: encrypt.format
-
- If this is set to ``luks``, it requests that the qcow2 payload (not
- qcow2 header) be encrypted using the LUKS format. The passphrase to
- use to unlock the LUKS key slot is given by the ``encrypt.key-secret``
- parameter. LUKS encryption parameters can be tuned with the other
- ``encrypt.*`` parameters.
-
- If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
- The encryption key is given by the ``encrypt.key-secret`` parameter.
- This encryption format is considered to be flawed by modern cryptography
- standards, suffering from a number of design problems:
-
- - The AES-CBC cipher is used with predictable initialization vectors based
- on the sector number. This makes it vulnerable to chosen plaintext
attacks
- which can reveal the existence of encrypted data.
- - The user passphrase is directly used as the encryption key. A poorly
- chosen or short passphrase will compromise the security of the
encryption.
- - In the event of the passphrase being compromised there is no way to
- change the passphrase to protect data in any qcow images. The files must
- be cloned, using a different encryption passphrase in the new file. The
- original file must then be securely erased using a program like shred,
- though even this is ineffective with many modern storage technologies.
-
- The use of this is no longer supported in system emulators. Support only
- remains in the command line utilities, for the purposes of data liberation
- and interoperability with old versions of QEMU. The ``luks`` format
- should be used instead.
-
- .. option:: encrypt.key-secret
-
- Provides the ID of a ``secret`` object that contains the passphrase
- (``encrypt.format=luks``) or encryption key (``encrypt.format=aes``).
-
- .. option:: encrypt.cipher-alg
-
- Name of the cipher algorithm and key length. Currently defaults
- to ``aes-256``. Only used when ``encrypt.format=luks``.
-
- .. option:: encrypt.cipher-mode
-
- Name of the encryption mode to use. Currently defaults to ``xts``.
- Only used when ``encrypt.format=luks``.
-
- .. option:: encrypt.ivgen-alg
-
- Name of the initialization vector generator algorithm. Currently defaults
- to ``plain64``. Only used when ``encrypt.format=luks``.
-
- .. option:: encrypt.ivgen-hash-alg
-
- Name of the hash algorithm to use with the initialization vector generator
- (if required). Defaults to ``sha256``. Only used when
``encrypt.format=luks``.
-
- .. option:: encrypt.hash-alg
-
- Name of the hash algorithm to use for PBKDF algorithm
- Defaults to ``sha256``. Only used when ``encrypt.format=luks``.
-
- .. option:: encrypt.iter-time
-
- Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
- Defaults to ``2000``. Only used when ``encrypt.format=luks``.
-
- .. option:: cluster_size
-
- Changes the qcow2 cluster size (must be between 512 and 2M). Smaller
cluster
- sizes can improve the image file size whereas larger cluster sizes
generally
- provide better performance.
-
- .. option:: preallocation
-
- Preallocation mode (allowed values: ``off``, ``metadata``, ``falloc``,
- ``full``). An image with preallocated metadata is initially larger but can
- improve performance when the image needs to grow. ``falloc`` and ``full``
- preallocations are like the same options of ``raw`` format, but sets up
- metadata also.
-
- .. option:: lazy_refcounts
-
- If this option is set to ``on``, reference count updates are postponed with
- the goal of avoiding metadata I/O and improving performance. This is
- particularly interesting with :option:`cache=writethrough` which doesn't
batch
- metadata updates. The tradeoff is that after a host crash, the reference
count
- tables must be rebuilt, i.e. on the next open an (automatic) ``qemu-img
- check -r all`` is required, which may take some time.
-
- This option can only be enabled if ``compat=1.1`` is specified.
-
- .. option:: nocow
-
- If this option is set to ``on``, it will turn off COW of the file. It's
only
- valid on btrfs, no effect on other file systems.
-
- Btrfs has low performance when hosting a VM image file, even more
- when the guest on the VM also using btrfs as file system. Turning off
- COW is a way to mitigate this bad performance. Generally there are two
- ways to turn off COW on btrfs:
-
- - Disable it by mounting with nodatacow, then all newly created files
- will be NOCOW.
- - For an empty file, add the NOCOW file attribute. That's what this
- option does.
-
- Note: this option is only valid to new or empty files. If there is
- an existing file which is COW and has data blocks already, it couldn't
- be changed to NOCOW by setting ``nocow=on``. One can issue ``lsattr
- filename`` to check if the NOCOW flag is set or not (Capital 'C' is
- NOCOW flag).
-
-.. program:: image-formats
-.. option:: qed
-
- Old QEMU image format with support for backing files and compact image files
- (when your filesystem or transport medium does not support holes).
-
- When converting QED images to qcow2, you might want to consider using the
- ``lazy_refcounts=on`` option to get a more QED-like behaviour.
-
- Supported options:
-
- .. program:: qed
- .. option:: backing_file
-
- File name of a base image (see ``create`` subcommand).
-
- .. option:: backing_fmt
-
- Image file format of backing file (optional). Useful if the format
cannot be
- autodetected because it has no header, like some vhd/vpc files.
-
- .. option:: cluster_size
-
- Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
- cluster sizes can improve the image file size whereas larger cluster sizes
- generally provide better performance.
-
- .. option:: table_size
-
- Changes the number of clusters per L1/L2 table (must be
- power-of-2 between 1 and 16). There is normally no need to
- change this value but this option can between used for
- performance benchmarking.
-
-.. program:: image-formats
-.. option:: qcow
-
- Old QEMU image format with support for backing files, compact image files,
- encryption and compression.
-
- Supported options:
-
- .. program:: qcow
- .. option:: backing_file
-
- File name of a base image (see ``create`` subcommand)
-
- .. option:: encryption
-
- This option is deprecated and equivalent to ``encrypt.format=aes``
-
- .. option:: encrypt.format
-
- If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
- The encryption key is given by the ``encrypt.key-secret`` parameter.
- This encryption format is considered to be flawed by modern cryptography
- standards, suffering from a number of design problems enumerated
previously
- against the ``qcow2`` image format.
-
- The use of this is no longer supported in system emulators. Support only
- remains in the command line utilities, for the purposes of data liberation
- and interoperability with old versions of QEMU.
-
- Users requiring native encryption should use the ``qcow2`` format
- instead with ``encrypt.format=luks``.
-
- .. option:: encrypt.key-secret
-
- Provides the ID of a ``secret`` object that contains the encryption
- key (``encrypt.format=aes``).
-
-.. program:: image-formats
-.. option:: luks
-
- LUKS v1 encryption format, compatible with Linux dm-crypt/cryptsetup
-
- Supported options:
-
- .. program:: luks
- .. option:: key-secret
-
- Provides the ID of a ``secret`` object that contains the passphrase.
-
- .. option:: cipher-alg
-
- Name of the cipher algorithm and key length. Currently defaults
- to ``aes-256``.
-
- .. option:: cipher-mode
-
- Name of the encryption mode to use. Currently defaults to ``xts``.
-
- .. option:: ivgen-alg
-
- Name of the initialization vector generator algorithm. Currently defaults
- to ``plain64``.
-
- .. option:: ivgen-hash-alg
-
- Name of the hash algorithm to use with the initialization vector generator
- (if required). Defaults to ``sha256``.
-
- .. option:: hash-alg
-
- Name of the hash algorithm to use for PBKDF algorithm
- Defaults to ``sha256``.
-
- .. option:: iter-time
-
- Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
- Defaults to ``2000``.
-
-.. program:: image-formats
-.. option:: vdi
-
- VirtualBox 1.1 compatible image format.
-
- Supported options:
-
- .. program:: vdi
- .. option:: static
-
- If this option is set to ``on``, the image is created with metadata
- preallocation.
-
-.. program:: image-formats
-.. option:: vmdk
-
- VMware 3 and 4 compatible image format.
-
- Supported options:
-
- .. program: vmdk
- .. option:: backing_file
-
- File name of a base image (see ``create`` subcommand).
-
- .. option:: compat6
-
- Create a VMDK version 6 image (instead of version 4)
-
- .. option:: hwversion
-
- Specify vmdk virtual hardware version. Compat6 flag cannot be enabled
- if hwversion is specified.
-
- .. option:: subformat
-
- Specifies which VMDK subformat to use. Valid options are
- ``monolithicSparse`` (default),
- ``monolithicFlat``,
- ``twoGbMaxExtentSparse``,
- ``twoGbMaxExtentFlat`` and
- ``streamOptimized``.
-
-.. program:: image-formats
-.. option:: vpc
-
- VirtualPC compatible image format (VHD).
-
- Supported options:
-
- .. program:: vpc
- .. option:: subformat
-
- Specifies which VHD subformat to use. Valid options are
- ``dynamic`` (default) and ``fixed``.
-
-.. program:: image-formats
-.. option:: VHDX
-
- Hyper-V compatible image format (VHDX).
-
- Supported options:
-
- .. program:: VHDX
- .. option:: subformat
-
- Specifies which VHDX subformat to use. Valid options are
- ``dynamic`` (default) and ``fixed``.
-
- .. option:: block_state_zero
-
- Force use of payload blocks of type 'ZERO'. Can be set to ``on``
(default)
- or ``off``. When set to ``off``, new blocks will be created as
- ``PAYLOAD_BLOCK_NOT_PRESENT``, which means parsers are free to return
- arbitrary data for those blocks. Do not set to ``off`` when using
- ``qemu-img convert`` with ``subformat=dynamic``.
-
- .. option:: block_size
-
- Block size; min 1 MB, max 256 MB. 0 means auto-calculate based on
- image size.
-
- .. option:: log_size
-
- Log size; min 1 MB.
-
-Read-only formats
------------------
-
-More disk image file formats are supported in a read-only mode.
-
-.. program:: image-formats
-.. option:: bochs
-
- Bochs images of ``growing`` type.
-
-.. program:: image-formats
-.. option:: cloop
-
- Linux Compressed Loop image, useful only to reuse directly compressed
- CD-ROM images present for example in the Knoppix CD-ROMs.
-
-.. program:: image-formats
-.. option:: dmg
-
- Apple disk image.
-
-.. program:: image-formats
-.. option:: parallels
-
- Parallels disk image format.
-
-Using host drives
------------------
-
-In addition to disk image files, QEMU can directly access host
-devices. We describe here the usage for QEMU version >= 0.8.3.
-
-Linux
-'''''
-
-On Linux, you can directly use the host device filename instead of a
-disk image filename provided you have enough privileges to access
-it. For example, use ``/dev/cdrom`` to access to the CDROM.
-
-CD
- You can specify a CDROM device even if no CDROM is loaded. QEMU has
- specific code to detect CDROM insertion or removal. CDROM ejection by
- the guest OS is supported. Currently only data CDs are supported.
-
-Floppy
- You can specify a floppy device even if no floppy is loaded. Floppy
- removal is currently not detected accurately (if you change floppy
- without doing floppy access while the floppy is not loaded, the guest
- OS will think that the same floppy is loaded).
- Use of the host's floppy device is deprecated, and support for it will
- be removed in a future release.
-
-Hard disks
- Hard disks can be used. Normally you must specify the whole disk
- (``/dev/hdb`` instead of ``/dev/hdb1``) so that the guest OS can
- see it as a partitioned disk. WARNING: unless you know what you do, it
- is better to only make READ-ONLY accesses to the hard disk otherwise
- you may corrupt your host data (use the ``-snapshot`` command
- line option or modify the device permissions accordingly).
-
-Windows
-'''''''
-
-CD
- The preferred syntax is the drive letter (e.g. ``d:``). The
- alternate syntax ``\\.\d:`` is supported. ``/dev/cdrom`` is
- supported as an alias to the first CDROM drive.
-
- Currently there is no specific code to handle removable media, so it
- is better to use the ``change`` or ``eject`` monitor commands to
- change or eject media.
-
-Hard disks
- Hard disks can be used with the syntax: ``\\.\PhysicalDriveN``
- where *N* is the drive number (0 is the first hard disk).
-
- WARNING: unless you know what you do, it is better to only make
- READ-ONLY accesses to the hard disk otherwise you may corrupt your
- host data (use the ``-snapshot`` command line so that the
- modifications are written in a temporary file).
-
-Mac OS X
-''''''''
-
-``/dev/cdrom`` is an alias to the first CDROM.
-
-Currently there is no specific code to handle removable media, so it
-is better to use the ``change`` or ``eject`` monitor commands to
-change or eject media.
-
-Virtual FAT disk images
------------------------
-
-QEMU can automatically create a virtual FAT disk image from a
-directory tree. In order to use it, just type:
-
-.. parsed-literal::
-
- |qemu_system| linux.img -hdb fat:/my_directory
-
-Then you access access to all the files in the ``/my_directory``
-directory without having to copy them in a disk image or to export
-them via SAMBA or NFS. The default access is *read-only*.
-
-Floppies can be emulated with the ``:floppy:`` option:
-
-.. parsed-literal::
-
- |qemu_system| linux.img -fda fat:floppy:/my_directory
-
-A read/write support is available for testing (beta stage) with the
-``:rw:`` option:
-
-.. parsed-literal::
-
- |qemu_system| linux.img -fda fat:floppy:rw:/my_directory
-
-What you should *never* do:
-
-- use non-ASCII filenames
-- use "-snapshot" together with ":rw:"
-- expect it to work when loadvm'ing
-- write to the FAT directory on the host system while accessing it with the
guest system
-
-NBD access
-----------
-
-QEMU can access directly to block device exported using the Network Block
Device
-protocol.
-
-.. parsed-literal::
-
- |qemu_system| linux.img -hdb nbd://my_nbd_server.mydomain.org:1024/
-
-If the NBD server is located on the same host, you can use an unix socket
instead
-of an inet socket:
-
-.. parsed-literal::
-
- |qemu_system| linux.img -hdb nbd+unix://?socket=/tmp/my_socket
-
-In this case, the block device must be exported using qemu-nbd:
-
-.. parsed-literal::
-
- qemu-nbd --socket=/tmp/my_socket my_disk.qcow2
-
-The use of qemu-nbd allows sharing of a disk between several guests:
-
-.. parsed-literal::
-
- qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2
-
-and then you can use it with two guests:
-
-.. parsed-literal::
-
- |qemu_system| linux1.img -hdb nbd+unix://?socket=/tmp/my_socket
- |qemu_system| linux2.img -hdb nbd+unix://?socket=/tmp/my_socket
-
-If the nbd-server uses named exports (supported since NBD 2.9.18, or with
QEMU's
-own embedded NBD server), you must specify an export name in the URI:
-
-.. parsed-literal::
-
- |qemu_system| -cdrom nbd://localhost/debian-500-ppc-netinst
- |qemu_system| -cdrom nbd://localhost/openSUSE-11.1-ppc-netinst
-
-The URI syntax for NBD is supported since QEMU 1.3. An alternative syntax is
-also available. Here are some example of the older syntax:
-
-.. parsed-literal::
-
- |qemu_system| linux.img -hdb nbd:my_nbd_server.mydomain.org:1024
- |qemu_system| linux2.img -hdb nbd:unix:/tmp/my_socket
- |qemu_system| -cdrom nbd:localhost:10809:exportname=debian-500-ppc-netinst
-
-
-
-Sheepdog disk images
---------------------
-
-Sheepdog is a distributed storage system for QEMU. It provides highly
-available block level storage volumes that can be attached to
-QEMU-based virtual machines.
-
-You can create a Sheepdog disk image with the command:
-
-.. parsed-literal::
-
- qemu-img create sheepdog:///IMAGE SIZE
-
-where *IMAGE* is the Sheepdog image name and *SIZE* is its
-size.
-
-To import the existing *FILENAME* to Sheepdog, you can use a
-convert command.
-
-.. parsed-literal::
-
- qemu-img convert FILENAME sheepdog:///IMAGE
-
-You can boot from the Sheepdog disk image with the command:
-
-.. parsed-literal::
-
- |qemu_system| sheepdog:///IMAGE
-
-You can also create a snapshot of the Sheepdog image like qcow2.
-
-.. parsed-literal::
-
- qemu-img snapshot -c TAG sheepdog:///IMAGE
-
-where *TAG* is a tag name of the newly created snapshot.
-
-To boot from the Sheepdog snapshot, specify the tag name of the
-snapshot.
-
-.. parsed-literal::
-
- |qemu_system| sheepdog:///IMAGE#TAG
-
-You can create a cloned image from the existing snapshot.
-
-.. parsed-literal::
-
- qemu-img create -b sheepdog:///BASE#TAG sheepdog:///IMAGE
-
-where *BASE* is an image name of the source snapshot and *TAG*
-is its tag name.
-
-You can use an unix socket instead of an inet socket:
-
-.. parsed-literal::
-
- |qemu_system| sheepdog+unix:///IMAGE?socket=PATH
-
-If the Sheepdog daemon doesn't run on the local host, you need to
-specify one of the Sheepdog servers to connect to.
-
-.. parsed-literal::
-
- qemu-img create sheepdog://HOSTNAME:PORT/IMAGE SIZE
- |qemu_system| sheepdog://HOSTNAME:PORT/IMAGE
-
-iSCSI LUNs
-----------
-
-iSCSI is a popular protocol used to access SCSI devices across a computer
-network.
-
-There are two different ways iSCSI devices can be used by QEMU.
-
-The first method is to mount the iSCSI LUN on the host, and make it appear as
-any other ordinary SCSI device on the host and then to access this device as a
-/dev/sd device from QEMU. How to do this differs between host OSes.
-
-The second method involves using the iSCSI initiator that is built into
-QEMU. This provides a mechanism that works the same way regardless of which
-host OS you are running QEMU on. This section will describe this second method
-of using iSCSI together with QEMU.
-
-In QEMU, iSCSI devices are described using special iSCSI URLs. URL syntax:
-
-::
-
- iscsi://[<username>[%<password>]@]<host>[:<port>]/<target-iqn-name>/<lun>
-
-Username and password are optional and only used if your target is set up
-using CHAP authentication for access control.
-Alternatively the username and password can also be set via environment
-variables to have these not show up in the process list:
-
-::
-
- export LIBISCSI_CHAP_USERNAME=<username>
- export LIBISCSI_CHAP_PASSWORD=<password>
- iscsi://<host>/<target-iqn-name>/<lun>
-
-Various session related parameters can be set via special options, either
-in a configuration file provided via '-readconfig' or directly on the
-command line.
-
-If the initiator-name is not specified qemu will use a default name
-of 'iqn.2008-11.org.linux-kvm[:<uuid>'] where <uuid> is the UUID of the
-virtual machine. If the UUID is not specified qemu will use
-'iqn.2008-11.org.linux-kvm[:<name>'] where <name> is the name of the
-virtual machine.
-
-Setting a specific initiator name to use when logging in to the target:
-
-::
-
- -iscsi initiator-name=iqn.qemu.test:my-initiator
-
-Controlling which type of header digest to negotiate with the target:
-
-::
-
- -iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
-
-These can also be set via a configuration file:
-
-::
-
- [iscsi]
- user = "CHAP username"
- password = "CHAP password"
- initiator-name = "iqn.qemu.test:my-initiator"
- # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
- header-digest = "CRC32C"
-
-Setting the target name allows different options for different targets:
-
-::
-
- [iscsi "iqn.target.name"]
- user = "CHAP username"
- password = "CHAP password"
- initiator-name = "iqn.qemu.test:my-initiator"
- # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
- header-digest = "CRC32C"
-
-How to use a configuration file to set iSCSI configuration options:
-
-.. parsed-literal::
-
- cat >iscsi.conf <<EOF
- [iscsi]
- user = "me"
- password = "my password"
- initiator-name = "iqn.qemu.test:my-initiator"
- header-digest = "CRC32C"
- EOF
-
- |qemu_system| -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
- -readconfig iscsi.conf
-
-How to set up a simple iSCSI target on loopback and access it via QEMU:
-this example shows how to set up an iSCSI target with one CDROM and one DISK
-using the Linux STGT software target. This target is available on Red Hat based
-systems as the package 'scsi-target-utils'.
-
-.. parsed-literal::
-
- tgtd --iscsi portal=127.0.0.1:3260
- tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.qemu.test
- tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1 \\
- -b /IMAGES/disk.img --device-type=disk
- tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 2 \\
- -b /IMAGES/cd.iso --device-type=cd
- tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
-
- |qemu_system| -iscsi initiator-name=iqn.qemu.test:my-initiator \\
- -boot d -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
- -cdrom iscsi://127.0.0.1/iqn.qemu.test/2
-
-GlusterFS disk images
----------------------
-
-GlusterFS is a user space distributed file system.
-
-You can boot from the GlusterFS disk image with the command:
-
-URI:
-
-.. parsed-literal::
-
- |qemu_system| -drive file=gluster[+TYPE]://[HOST}[:PORT]]/VOLUME/PATH
- [?socket=...][,file.debug=9][,file.logfile=...]
-
-JSON:
-
-.. parsed-literal::
-
- |qemu_system| 'json:{"driver":"qcow2",
- "file":{"driver":"gluster",
-
"volume":"testvol","path":"a.img","debug":9,"logfile":"...",
-
"server":[{"type":"tcp","host":"...","port":"..."},
-
{"type":"unix","socket":"..."}]}}'
-
-*gluster* is the protocol.
-
-*TYPE* specifies the transport type used to connect to gluster
-management daemon (glusterd). Valid transport types are
-tcp and unix. In the URI form, if a transport type isn't specified,
-then tcp type is assumed.
-
-*HOST* specifies the server where the volume file specification for
-the given volume resides. This can be either a hostname or an ipv4 address.
-If transport type is unix, then *HOST* field should not be specified.
-Instead *socket* field needs to be populated with the path to unix domain
-socket.
-
-*PORT* is the port number on which glusterd is listening. This is optional
-and if not specified, it defaults to port 24007. If the transport type is unix,
-then *PORT* should not be specified.
-
-*VOLUME* is the name of the gluster volume which contains the disk image.
-
-*PATH* is the path to the actual disk image that resides on gluster volume.
-
-*debug* is the logging level of the gluster protocol driver. Debug levels
-are 0-9, with 9 being the most verbose, and 0 representing no debugging output.
-The default level is 4. The current logging levels defined in the gluster
source
-are 0 - None, 1 - Emergency, 2 - Alert, 3 - Critical, 4 - Error, 5 - Warning,
-6 - Notice, 7 - Info, 8 - Debug, 9 - Trace
-
-*logfile* is a commandline option to mention log file path which helps in
-logging to the specified file and also help in persisting the gfapi logs. The
-default is stderr.
-
-You can create a GlusterFS disk image with the command:
-
-.. parsed-literal::
-
- qemu-img create gluster://HOST/VOLUME/PATH SIZE
-
-Examples
-
-.. parsed-literal::
-
- |qemu_system| -drive file=gluster://1.2.3.4/testvol/a.img
- |qemu_system| -drive file=gluster+tcp://1.2.3.4/testvol/a.img
- |qemu_system| -drive file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
- |qemu_system| -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]/testvol/dir/a.img
- |qemu_system| -drive
file=gluster+tcp://[1:2:3:4:5:6:7:8]:24007/testvol/dir/a.img
- |qemu_system| -drive
file=gluster+tcp://server.domain.com:24007/testvol/dir/a.img
- |qemu_system| -drive
file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
- |qemu_system| -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img
- |qemu_system| -drive
file=gluster://1.2.3.4/testvol/a.img,file.debug=9,file.logfile=/var/log/qemu-gluster.log
- |qemu_system| 'json:{"driver":"qcow2",
- "file":{"driver":"gluster",
- "volume":"testvol","path":"a.img",
-
"debug":9,"logfile":"/var/log/qemu-gluster.log",
-
"server":[{"type":"tcp","host":"1.2.3.4","port":24007},
-
{"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
- |qemu_system| -drive
driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
-
file.debug=9,file.logfile=/var/log/qemu-gluster.log,
-
file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
-
file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
-
-Secure Shell (ssh) disk images
-------------------------------
-
-You can access disk images located on a remote ssh server
-by using the ssh protocol:
-
-.. parsed-literal::
-
- |qemu_system| -drive
file=ssh://[USER@]SERVER[:PORT]/PATH[?host_key_check=HOST_KEY_CHECK]
-
-Alternative syntax using properties:
-
-.. parsed-literal::
-
- |qemu_system| -drive
file.driver=ssh[,file.user=USER],file.host=SERVER[,file.port=PORT],file.path=PATH[,file.host_key_check=HOST_KEY_CHECK]
-
-*ssh* is the protocol.
-
-*USER* is the remote user. If not specified, then the local
-username is tried.
-
-*SERVER* specifies the remote ssh server. Any ssh server can be
-used, but it must implement the sftp-server protocol. Most Unix/Linux
-systems should work without requiring any extra configuration.
-
-*PORT* is the port number on which sshd is listening. By default
-the standard ssh port (22) is used.
-
-*PATH* is the path to the disk image.
-
-The optional *HOST_KEY_CHECK* parameter controls how the remote
-host's key is checked. The default is ``yes`` which means to use
-the local ``.ssh/known_hosts`` file. Setting this to ``no``
-turns off known-hosts checking. Or you can check that the host key
-matches a specific fingerprint:
-``host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8``
-(``sha1:`` can also be used as a prefix, but note that OpenSSH
-tools only use MD5 to print fingerprints).
-
-Currently authentication must be done using ssh-agent. Other
-authentication methods may be supported in future.
-
-Note: Many ssh servers do not support an ``fsync``-style operation.
-The ssh driver cannot guarantee that disk flush requests are
-obeyed, and this causes a risk of disk corruption if the remote
-server or network goes down during writes. The driver will
-print a warning when ``fsync`` is not supported:
-
-::
-
- warning: ssh server ssh.example.com:22 does not support fsync
-
-With sufficiently new versions of libssh and OpenSSH, ``fsync`` is
-supported.
-
-NVMe disk images
-----------------
-
-NVM Express (NVMe) storage controllers can be accessed directly by a userspace
-driver in QEMU. This bypasses the host kernel file system and block layers
-while retaining QEMU block layer functionalities, such as block jobs, I/O
-throttling, image formats, etc. Disk I/O performance is typically higher than
-with ``-drive file=/dev/sda`` using either thread pool or linux-aio.
-
-The controller will be exclusively used by the QEMU process once started. To be
-able to share storage between multiple VMs and other applications on the host,
-please use the file based protocols.
-
-Before starting QEMU, bind the host NVMe controller to the host vfio-pci
-driver. For example:
-
-.. parsed-literal::
-
- # modprobe vfio-pci
- # lspci -n -s 0000:06:0d.0
- 06:0d.0 0401: 1102:0002 (rev 08)
- # echo 0000:06:0d.0 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind
- # echo 1102 0002 > /sys/bus/pci/drivers/vfio-pci/new_id
-
- # |qemu_system| -drive file=nvme://HOST:BUS:SLOT.FUNC/NAMESPACE
-
-Alternative syntax using properties:
-
-.. parsed-literal::
-
- |qemu_system| -drive
file.driver=nvme,file.device=HOST:BUS:SLOT.FUNC,file.namespace=NAMESPACE
-
-*HOST*:*BUS*:*SLOT*.\ *FUNC* is the NVMe controller's PCI device
-address on the host.
-
-*NAMESPACE* is the NVMe namespace number, starting from 1.
-
-Disk image file locking
------------------------
-
-By default, QEMU tries to protect image files from unexpected concurrent
-access, as long as it's supported by the block protocol driver and host
-operating system. If multiple QEMU processes (including QEMU emulators and
-utilities) try to open the same image with conflicting accessing modes, all but
-the first one will get an error.
-
-This feature is currently supported by the file protocol on Linux with the Open
-File Descriptor (OFD) locking API, and can be configured to fall back to POSIX
-locking if the POSIX host doesn't support Linux OFD locking.
-
-To explicitly enable image locking, specify "locking=on" in the file protocol
-driver options. If OFD locking is not possible, a warning will be printed and
-the POSIX locking API will be used. In this case there is a risk that the lock
-will get silently lost when doing hot plugging and block jobs, due to the
-shortcomings of the POSIX locking API.
-
-QEMU transparently handles lock handover during shared storage migration. For
-shared virtual disk images between multiple VMs, the "share-rw" device option
-should be used.
-
-By default, the guest has exclusive write access to its disk image. If the
-guest can safely share the disk image with other writers the
-``-device ...,share-rw=on`` parameter can be used. This is only safe if
-the guest is running software, such as a cluster file system, that
-coordinates disk accesses to avoid corruption.
-
-Note that share-rw=on only declares the guest's ability to share the disk.
-Some QEMU features, such as image file formats, require exclusive write access
-to the disk image and this is unaffected by the share-rw=on option.
-
-Alternatively, locking can be fully disabled by "locking=off" block device
-option. In the command line, the option is usually in the form of
-"file.locking=off" as the protocol driver is normally placed as a "file" child
-under a format driver. For example:
-
-::
+Synopsis
+--------
- -blockdev
driver=qcow2,file.filename=/path/to/image,file.locking=off,file.driver=file
+QEMU block driver reference manual
-To check if image locking is active, check the output of the "lslocks" command
-on host and see if there are locks held by the QEMU process on the image file.
-More than one byte could be locked by the QEMU instance, each byte of which
-reflects a particular permission that is acquired or protected by the running
-block driver.
+Description
+-----------
-.. only:: man
+.. include:: qemu-block-drivers.rst.inc
- See also
- --------
+See also
+--------
- The HTML documentation of QEMU for more precise information and Linux
- user mode emulator invocation.
+The HTML documentation of QEMU for more precise information and Linux
+user mode emulator invocation.
diff --git a/docs/system/qemu-block-drivers.rst.inc
b/docs/system/qemu-block-drivers.rst.inc
new file mode 100644
index 0000000000..b052a6d14e
--- /dev/null
+++ b/docs/system/qemu-block-drivers.rst.inc
@@ -0,0 +1,954 @@
+Disk image file formats
+~~~~~~~~~~~~~~~~~~~~~~~
+
+QEMU supports many image file formats that can be used with VMs as well as with
+any of the tools (like ``qemu-img``). This includes the preferred formats
+raw and qcow2 as well as formats that are supported for compatibility with
+older QEMU versions or other hypervisors.
+
+Depending on the image format, different options can be passed to
+``qemu-img create`` and ``qemu-img convert`` using the ``-o`` option.
+This section describes each format and the options that are supported for it.
+
+.. program:: image-formats
+.. option:: raw
+
+ Raw disk image format. This format has the advantage of
+ being simple and easily exportable to all other emulators. If your
+ file system supports *holes* (for example in ext2 or ext3 on
+ Linux or NTFS on Windows), then only the written sectors will reserve
+ space. Use ``qemu-img info`` to know the real size used by the
+ image or ``ls -ls`` on Unix/Linux.
+
+ Supported options:
+
+ .. program:: raw
+ .. option:: preallocation
+
+ Preallocation mode (allowed values: ``off``, ``falloc``,
+ ``full``). ``falloc`` mode preallocates space for image by
+ calling ``posix_fallocate()``. ``full`` mode preallocates space
+ for image by writing data to underlying storage. This data may or
+ may not be zero, depending on the storage location.
+
+.. program:: image-formats
+.. option:: qcow2
+
+ QEMU image format, the most versatile format. Use it to have smaller
+ images (useful if your filesystem does not supports holes, for example
+ on Windows), zlib based compression and support of multiple VM
+ snapshots.
+
+ Supported options:
+
+ .. program:: qcow2
+ .. option:: compat
+
+ Determines the qcow2 version to use. ``compat=0.10`` uses the
+ traditional image format that can be read by any QEMU since 0.10.
+ ``compat=1.1`` enables image format extensions that only QEMU 1.1 and
+ newer understand (this is the default). Amongst others, this includes
+ zero clusters, which allow efficient copy-on-read for sparse images.
+
+ .. option:: backing_file
+
+ File name of a base image (see ``create`` subcommand)
+
+ .. option:: backing_fmt
+
+ Image format of the base image
+
+ .. option:: encryption
+
+ This option is deprecated and equivalent to ``encrypt.format=aes``
+
+ .. option:: encrypt.format
+
+ If this is set to ``luks``, it requests that the qcow2 payload (not
+ qcow2 header) be encrypted using the LUKS format. The passphrase to
+ use to unlock the LUKS key slot is given by the ``encrypt.key-secret``
+ parameter. LUKS encryption parameters can be tuned with the other
+ ``encrypt.*`` parameters.
+
+ If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
+ The encryption key is given by the ``encrypt.key-secret`` parameter.
+ This encryption format is considered to be flawed by modern cryptography
+ standards, suffering from a number of design problems:
+
+ - The AES-CBC cipher is used with predictable initialization vectors based
+ on the sector number. This makes it vulnerable to chosen plaintext
attacks
+ which can reveal the existence of encrypted data.
+ - The user passphrase is directly used as the encryption key. A poorly
+ chosen or short passphrase will compromise the security of the
encryption.
+ - In the event of the passphrase being compromised there is no way to
+ change the passphrase to protect data in any qcow images. The files must
+ be cloned, using a different encryption passphrase in the new file. The
+ original file must then be securely erased using a program like shred,
+ though even this is ineffective with many modern storage technologies.
+
+ The use of this is no longer supported in system emulators. Support only
+ remains in the command line utilities, for the purposes of data liberation
+ and interoperability with old versions of QEMU. The ``luks`` format
+ should be used instead.
+
+ .. option:: encrypt.key-secret
+
+ Provides the ID of a ``secret`` object that contains the passphrase
+ (``encrypt.format=luks``) or encryption key (``encrypt.format=aes``).
+
+ .. option:: encrypt.cipher-alg
+
+ Name of the cipher algorithm and key length. Currently defaults
+ to ``aes-256``. Only used when ``encrypt.format=luks``.
+
+ .. option:: encrypt.cipher-mode
+
+ Name of the encryption mode to use. Currently defaults to ``xts``.
+ Only used when ``encrypt.format=luks``.
+
+ .. option:: encrypt.ivgen-alg
+
+ Name of the initialization vector generator algorithm. Currently defaults
+ to ``plain64``. Only used when ``encrypt.format=luks``.
+
+ .. option:: encrypt.ivgen-hash-alg
+
+ Name of the hash algorithm to use with the initialization vector generator
+ (if required). Defaults to ``sha256``. Only used when
``encrypt.format=luks``.
+
+ .. option:: encrypt.hash-alg
+
+ Name of the hash algorithm to use for PBKDF algorithm
+ Defaults to ``sha256``. Only used when ``encrypt.format=luks``.
+
+ .. option:: encrypt.iter-time
+
+ Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
+ Defaults to ``2000``. Only used when ``encrypt.format=luks``.
+
+ .. option:: cluster_size
+
+ Changes the qcow2 cluster size (must be between 512 and 2M). Smaller
cluster
+ sizes can improve the image file size whereas larger cluster sizes
generally
+ provide better performance.
+
+ .. option:: preallocation
+
+ Preallocation mode (allowed values: ``off``, ``metadata``, ``falloc``,
+ ``full``). An image with preallocated metadata is initially larger but can
+ improve performance when the image needs to grow. ``falloc`` and ``full``
+ preallocations are like the same options of ``raw`` format, but sets up
+ metadata also.
+
+ .. option:: lazy_refcounts
+
+ If this option is set to ``on``, reference count updates are postponed with
+ the goal of avoiding metadata I/O and improving performance. This is
+ particularly interesting with :option:`cache=writethrough` which doesn't
batch
+ metadata updates. The tradeoff is that after a host crash, the reference
count
+ tables must be rebuilt, i.e. on the next open an (automatic) ``qemu-img
+ check -r all`` is required, which may take some time.
+
+ This option can only be enabled if ``compat=1.1`` is specified.
+
+ .. option:: nocow
+
+ If this option is set to ``on``, it will turn off COW of the file. It's
only
+ valid on btrfs, no effect on other file systems.
+
+ Btrfs has low performance when hosting a VM image file, even more
+ when the guest on the VM also using btrfs as file system. Turning off
+ COW is a way to mitigate this bad performance. Generally there are two
+ ways to turn off COW on btrfs:
+
+ - Disable it by mounting with nodatacow, then all newly created files
+ will be NOCOW.
+ - For an empty file, add the NOCOW file attribute. That's what this
+ option does.
+
+ Note: this option is only valid to new or empty files. If there is
+ an existing file which is COW and has data blocks already, it couldn't
+ be changed to NOCOW by setting ``nocow=on``. One can issue ``lsattr
+ filename`` to check if the NOCOW flag is set or not (Capital 'C' is
+ NOCOW flag).
+
+.. program:: image-formats
+.. option:: qed
+
+ Old QEMU image format with support for backing files and compact image files
+ (when your filesystem or transport medium does not support holes).
+
+ When converting QED images to qcow2, you might want to consider using the
+ ``lazy_refcounts=on`` option to get a more QED-like behaviour.
+
+ Supported options:
+
+ .. program:: qed
+ .. option:: backing_file
+
+ File name of a base image (see ``create`` subcommand).
+
+ .. option:: backing_fmt
+
+ Image file format of backing file (optional). Useful if the format
cannot be
+ autodetected because it has no header, like some vhd/vpc files.
+
+ .. option:: cluster_size
+
+ Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
+ cluster sizes can improve the image file size whereas larger cluster sizes
+ generally provide better performance.
+
+ .. option:: table_size
+
+ Changes the number of clusters per L1/L2 table (must be
+ power-of-2 between 1 and 16). There is normally no need to
+ change this value but this option can between used for
+ performance benchmarking.
+
+.. program:: image-formats
+.. option:: qcow
+
+ Old QEMU image format with support for backing files, compact image files,
+ encryption and compression.
+
+ Supported options:
+
+ .. program:: qcow
+ .. option:: backing_file
+
+ File name of a base image (see ``create`` subcommand)
+
+ .. option:: encryption
+
+ This option is deprecated and equivalent to ``encrypt.format=aes``
+
+ .. option:: encrypt.format
+
+ If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
+ The encryption key is given by the ``encrypt.key-secret`` parameter.
+ This encryption format is considered to be flawed by modern cryptography
+ standards, suffering from a number of design problems enumerated
previously
+ against the ``qcow2`` image format.
+
+ The use of this is no longer supported in system emulators. Support only
+ remains in the command line utilities, for the purposes of data liberation
+ and interoperability with old versions of QEMU.
+
+ Users requiring native encryption should use the ``qcow2`` format
+ instead with ``encrypt.format=luks``.
+
+ .. option:: encrypt.key-secret
+
+ Provides the ID of a ``secret`` object that contains the encryption
+ key (``encrypt.format=aes``).
+
+.. program:: image-formats
+.. option:: luks
+
+ LUKS v1 encryption format, compatible with Linux dm-crypt/cryptsetup
+
+ Supported options:
+
+ .. program:: luks
+ .. option:: key-secret
+
+ Provides the ID of a ``secret`` object that contains the passphrase.
+
+ .. option:: cipher-alg
+
+ Name of the cipher algorithm and key length. Currently defaults
+ to ``aes-256``.
+
+ .. option:: cipher-mode
+
+ Name of the encryption mode to use. Currently defaults to ``xts``.
+
+ .. option:: ivgen-alg
+
+ Name of the initialization vector generator algorithm. Currently defaults
+ to ``plain64``.
+
+ .. option:: ivgen-hash-alg
+
+ Name of the hash algorithm to use with the initialization vector generator
+ (if required). Defaults to ``sha256``.
+
+ .. option:: hash-alg
+
+ Name of the hash algorithm to use for PBKDF algorithm
+ Defaults to ``sha256``.
+
+ .. option:: iter-time
+
+ Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
+ Defaults to ``2000``.
+
+.. program:: image-formats
+.. option:: vdi
+
+ VirtualBox 1.1 compatible image format.
+
+ Supported options:
+
+ .. program:: vdi
+ .. option:: static
+
+ If this option is set to ``on``, the image is created with metadata
+ preallocation.
+
+.. program:: image-formats
+.. option:: vmdk
+
+ VMware 3 and 4 compatible image format.
+
+ Supported options:
+
+ .. program: vmdk
+ .. option:: backing_file
+
+ File name of a base image (see ``create`` subcommand).
+
+ .. option:: compat6
+
+ Create a VMDK version 6 image (instead of version 4)
+
+ .. option:: hwversion
+
+ Specify vmdk virtual hardware version. Compat6 flag cannot be enabled
+ if hwversion is specified.
+
+ .. option:: subformat
+
+ Specifies which VMDK subformat to use. Valid options are
+ ``monolithicSparse`` (default),
+ ``monolithicFlat``,
+ ``twoGbMaxExtentSparse``,
+ ``twoGbMaxExtentFlat`` and
+ ``streamOptimized``.
+
+.. program:: image-formats
+.. option:: vpc
+
+ VirtualPC compatible image format (VHD).
+
+ Supported options:
+
+ .. program:: vpc
+ .. option:: subformat
+
+ Specifies which VHD subformat to use. Valid options are
+ ``dynamic`` (default) and ``fixed``.
+
+.. program:: image-formats
+.. option:: VHDX
+
+ Hyper-V compatible image format (VHDX).
+
+ Supported options:
+
+ .. program:: VHDX
+ .. option:: subformat
+
+ Specifies which VHDX subformat to use. Valid options are
+ ``dynamic`` (default) and ``fixed``.
+
+ .. option:: block_state_zero
+
+ Force use of payload blocks of type 'ZERO'. Can be set to ``on``
(default)
+ or ``off``. When set to ``off``, new blocks will be created as
+ ``PAYLOAD_BLOCK_NOT_PRESENT``, which means parsers are free to return
+ arbitrary data for those blocks. Do not set to ``off`` when using
+ ``qemu-img convert`` with ``subformat=dynamic``.
+
+ .. option:: block_size
+
+ Block size; min 1 MB, max 256 MB. 0 means auto-calculate based on
+ image size.
+
+ .. option:: log_size
+
+ Log size; min 1 MB.
+
+Read-only formats
+~~~~~~~~~~~~~~~~~
+
+More disk image file formats are supported in a read-only mode.
+
+.. program:: image-formats
+.. option:: bochs
+
+ Bochs images of ``growing`` type.
+
+.. program:: image-formats
+.. option:: cloop
+
+ Linux Compressed Loop image, useful only to reuse directly compressed
+ CD-ROM images present for example in the Knoppix CD-ROMs.
+
+.. program:: image-formats
+.. option:: dmg
+
+ Apple disk image.
+
+.. program:: image-formats
+.. option:: parallels
+
+ Parallels disk image format.
+
+Using host drives
+~~~~~~~~~~~~~~~~~
+
+In addition to disk image files, QEMU can directly access host
+devices. We describe here the usage for QEMU version >= 0.8.3.
+
+Linux
+^^^^^
+
+On Linux, you can directly use the host device filename instead of a
+disk image filename provided you have enough privileges to access
+it. For example, use ``/dev/cdrom`` to access to the CDROM.
+
+CD
+ You can specify a CDROM device even if no CDROM is loaded. QEMU has
+ specific code to detect CDROM insertion or removal. CDROM ejection by
+ the guest OS is supported. Currently only data CDs are supported.
+
+Floppy
+ You can specify a floppy device even if no floppy is loaded. Floppy
+ removal is currently not detected accurately (if you change floppy
+ without doing floppy access while the floppy is not loaded, the guest
+ OS will think that the same floppy is loaded).
+ Use of the host's floppy device is deprecated, and support for it will
+ be removed in a future release.
+
+Hard disks
+ Hard disks can be used. Normally you must specify the whole disk
+ (``/dev/hdb`` instead of ``/dev/hdb1``) so that the guest OS can
+ see it as a partitioned disk. WARNING: unless you know what you do, it
+ is better to only make READ-ONLY accesses to the hard disk otherwise
+ you may corrupt your host data (use the ``-snapshot`` command
+ line option or modify the device permissions accordingly).
+
+Windows
+^^^^^^^
+
+CD
+ The preferred syntax is the drive letter (e.g. ``d:``). The
+ alternate syntax ``\\.\d:`` is supported. ``/dev/cdrom`` is
+ supported as an alias to the first CDROM drive.
+
+ Currently there is no specific code to handle removable media, so it
+ is better to use the ``change`` or ``eject`` monitor commands to
+ change or eject media.
+
+Hard disks
+ Hard disks can be used with the syntax: ``\\.\PhysicalDriveN``
+ where *N* is the drive number (0 is the first hard disk).
+
+ WARNING: unless you know what you do, it is better to only make
+ READ-ONLY accesses to the hard disk otherwise you may corrupt your
+ host data (use the ``-snapshot`` command line so that the
+ modifications are written in a temporary file).
+
+Mac OS X
+^^^^^^^^
+
+``/dev/cdrom`` is an alias to the first CDROM.
+
+Currently there is no specific code to handle removable media, so it
+is better to use the ``change`` or ``eject`` monitor commands to
+change or eject media.
+
+Virtual FAT disk images
+~~~~~~~~~~~~~~~~~~~~~~~
+
+QEMU can automatically create a virtual FAT disk image from a
+directory tree. In order to use it, just type:
+
+.. parsed-literal::
+
+ |qemu_system| linux.img -hdb fat:/my_directory
+
+Then you access access to all the files in the ``/my_directory``
+directory without having to copy them in a disk image or to export
+them via SAMBA or NFS. The default access is *read-only*.
+
+Floppies can be emulated with the ``:floppy:`` option:
+
+.. parsed-literal::
+
+ |qemu_system| linux.img -fda fat:floppy:/my_directory
+
+A read/write support is available for testing (beta stage) with the
+``:rw:`` option:
+
+.. parsed-literal::
+
+ |qemu_system| linux.img -fda fat:floppy:rw:/my_directory
+
+What you should *never* do:
+
+- use non-ASCII filenames
+- use "-snapshot" together with ":rw:"
+- expect it to work when loadvm'ing
+- write to the FAT directory on the host system while accessing it with the
guest system
+
+NBD access
+~~~~~~~~~~
+
+QEMU can access directly to block device exported using the Network Block
Device
+protocol.
+
+.. parsed-literal::
+
+ |qemu_system| linux.img -hdb nbd://my_nbd_server.mydomain.org:1024/
+
+If the NBD server is located on the same host, you can use an unix socket
instead
+of an inet socket:
+
+.. parsed-literal::
+
+ |qemu_system| linux.img -hdb nbd+unix://?socket=/tmp/my_socket
+
+In this case, the block device must be exported using qemu-nbd:
+
+.. parsed-literal::
+
+ qemu-nbd --socket=/tmp/my_socket my_disk.qcow2
+
+The use of qemu-nbd allows sharing of a disk between several guests:
+
+.. parsed-literal::
+
+ qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2
+
+and then you can use it with two guests:
+
+.. parsed-literal::
+
+ |qemu_system| linux1.img -hdb nbd+unix://?socket=/tmp/my_socket
+ |qemu_system| linux2.img -hdb nbd+unix://?socket=/tmp/my_socket
+
+If the nbd-server uses named exports (supported since NBD 2.9.18, or with
QEMU's
+own embedded NBD server), you must specify an export name in the URI:
+
+.. parsed-literal::
+
+ |qemu_system| -cdrom nbd://localhost/debian-500-ppc-netinst
+ |qemu_system| -cdrom nbd://localhost/openSUSE-11.1-ppc-netinst
+
+The URI syntax for NBD is supported since QEMU 1.3. An alternative syntax is
+also available. Here are some example of the older syntax:
+
+.. parsed-literal::
+
+ |qemu_system| linux.img -hdb nbd:my_nbd_server.mydomain.org:1024
+ |qemu_system| linux2.img -hdb nbd:unix:/tmp/my_socket
+ |qemu_system| -cdrom nbd:localhost:10809:exportname=debian-500-ppc-netinst
+
+
+
+Sheepdog disk images
+~~~~~~~~~~~~~~~~~~~~
+
+Sheepdog is a distributed storage system for QEMU. It provides highly
+available block level storage volumes that can be attached to
+QEMU-based virtual machines.
+
+You can create a Sheepdog disk image with the command:
+
+.. parsed-literal::
+
+ qemu-img create sheepdog:///IMAGE SIZE
+
+where *IMAGE* is the Sheepdog image name and *SIZE* is its
+size.
+
+To import the existing *FILENAME* to Sheepdog, you can use a
+convert command.
+
+.. parsed-literal::
+
+ qemu-img convert FILENAME sheepdog:///IMAGE
+
+You can boot from the Sheepdog disk image with the command:
+
+.. parsed-literal::
+
+ |qemu_system| sheepdog:///IMAGE
+
+You can also create a snapshot of the Sheepdog image like qcow2.
+
+.. parsed-literal::
+
+ qemu-img snapshot -c TAG sheepdog:///IMAGE
+
+where *TAG* is a tag name of the newly created snapshot.
+
+To boot from the Sheepdog snapshot, specify the tag name of the
+snapshot.
+
+.. parsed-literal::
+
+ |qemu_system| sheepdog:///IMAGE#TAG
+
+You can create a cloned image from the existing snapshot.
+
+.. parsed-literal::
+
+ qemu-img create -b sheepdog:///BASE#TAG sheepdog:///IMAGE
+
+where *BASE* is an image name of the source snapshot and *TAG*
+is its tag name.
+
+You can use an unix socket instead of an inet socket:
+
+.. parsed-literal::
+
+ |qemu_system| sheepdog+unix:///IMAGE?socket=PATH
+
+If the Sheepdog daemon doesn't run on the local host, you need to
+specify one of the Sheepdog servers to connect to.
+
+.. parsed-literal::
+
+ qemu-img create sheepdog://HOSTNAME:PORT/IMAGE SIZE
+ |qemu_system| sheepdog://HOSTNAME:PORT/IMAGE
+
+iSCSI LUNs
+~~~~~~~~~~
+
+iSCSI is a popular protocol used to access SCSI devices across a computer
+network.
+
+There are two different ways iSCSI devices can be used by QEMU.
+
+The first method is to mount the iSCSI LUN on the host, and make it appear as
+any other ordinary SCSI device on the host and then to access this device as a
+/dev/sd device from QEMU. How to do this differs between host OSes.
+
+The second method involves using the iSCSI initiator that is built into
+QEMU. This provides a mechanism that works the same way regardless of which
+host OS you are running QEMU on. This section will describe this second method
+of using iSCSI together with QEMU.
+
+In QEMU, iSCSI devices are described using special iSCSI URLs. URL syntax:
+
+::
+
+ iscsi://[<username>[%<password>]@]<host>[:<port>]/<target-iqn-name>/<lun>
+
+Username and password are optional and only used if your target is set up
+using CHAP authentication for access control.
+Alternatively the username and password can also be set via environment
+variables to have these not show up in the process list:
+
+::
+
+ export LIBISCSI_CHAP_USERNAME=<username>
+ export LIBISCSI_CHAP_PASSWORD=<password>
+ iscsi://<host>/<target-iqn-name>/<lun>
+
+Various session related parameters can be set via special options, either
+in a configuration file provided via '-readconfig' or directly on the
+command line.
+
+If the initiator-name is not specified qemu will use a default name
+of 'iqn.2008-11.org.linux-kvm[:<uuid>'] where <uuid> is the UUID of the
+virtual machine. If the UUID is not specified qemu will use
+'iqn.2008-11.org.linux-kvm[:<name>'] where <name> is the name of the
+virtual machine.
+
+Setting a specific initiator name to use when logging in to the target:
+
+::
+
+ -iscsi initiator-name=iqn.qemu.test:my-initiator
+
+Controlling which type of header digest to negotiate with the target:
+
+::
+
+ -iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
+
+These can also be set via a configuration file:
+
+::
+
+ [iscsi]
+ user = "CHAP username"
+ password = "CHAP password"
+ initiator-name = "iqn.qemu.test:my-initiator"
+ # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
+ header-digest = "CRC32C"
+
+Setting the target name allows different options for different targets:
+
+::
+
+ [iscsi "iqn.target.name"]
+ user = "CHAP username"
+ password = "CHAP password"
+ initiator-name = "iqn.qemu.test:my-initiator"
+ # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
+ header-digest = "CRC32C"
+
+How to use a configuration file to set iSCSI configuration options:
+
+.. parsed-literal::
+
+ cat >iscsi.conf <<EOF
+ [iscsi]
+ user = "me"
+ password = "my password"
+ initiator-name = "iqn.qemu.test:my-initiator"
+ header-digest = "CRC32C"
+ EOF
+
+ |qemu_system| -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
+ -readconfig iscsi.conf
+
+How to set up a simple iSCSI target on loopback and access it via QEMU:
+this example shows how to set up an iSCSI target with one CDROM and one DISK
+using the Linux STGT software target. This target is available on Red Hat based
+systems as the package 'scsi-target-utils'.
+
+.. parsed-literal::
+
+ tgtd --iscsi portal=127.0.0.1:3260
+ tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.qemu.test
+ tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1 \\
+ -b /IMAGES/disk.img --device-type=disk
+ tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 2 \\
+ -b /IMAGES/cd.iso --device-type=cd
+ tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
+
+ |qemu_system| -iscsi initiator-name=iqn.qemu.test:my-initiator \\
+ -boot d -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
+ -cdrom iscsi://127.0.0.1/iqn.qemu.test/2
+
+GlusterFS disk images
+~~~~~~~~~~~~~~~~~~~~~
+
+GlusterFS is a user space distributed file system.
+
+You can boot from the GlusterFS disk image with the command:
+
+URI:
+
+.. parsed-literal::
+
+ |qemu_system| -drive file=gluster[+TYPE]://[HOST}[:PORT]]/VOLUME/PATH
+ [?socket=...][,file.debug=9][,file.logfile=...]
+
+JSON:
+
+.. parsed-literal::
+
+ |qemu_system| 'json:{"driver":"qcow2",
+ "file":{"driver":"gluster",
+
"volume":"testvol","path":"a.img","debug":9,"logfile":"...",
+
"server":[{"type":"tcp","host":"...","port":"..."},
+
{"type":"unix","socket":"..."}]}}'
+
+*gluster* is the protocol.
+
+*TYPE* specifies the transport type used to connect to gluster
+management daemon (glusterd). Valid transport types are
+tcp and unix. In the URI form, if a transport type isn't specified,
+then tcp type is assumed.
+
+*HOST* specifies the server where the volume file specification for
+the given volume resides. This can be either a hostname or an ipv4 address.
+If transport type is unix, then *HOST* field should not be specified.
+Instead *socket* field needs to be populated with the path to unix domain
+socket.
+
+*PORT* is the port number on which glusterd is listening. This is optional
+and if not specified, it defaults to port 24007. If the transport type is unix,
+then *PORT* should not be specified.
+
+*VOLUME* is the name of the gluster volume which contains the disk image.
+
+*PATH* is the path to the actual disk image that resides on gluster volume.
+
+*debug* is the logging level of the gluster protocol driver. Debug levels
+are 0-9, with 9 being the most verbose, and 0 representing no debugging output.
+The default level is 4. The current logging levels defined in the gluster
source
+are 0 - None, 1 - Emergency, 2 - Alert, 3 - Critical, 4 - Error, 5 - Warning,
+6 - Notice, 7 - Info, 8 - Debug, 9 - Trace
+
+*logfile* is a commandline option to mention log file path which helps in
+logging to the specified file and also help in persisting the gfapi logs. The
+default is stderr.
+
+You can create a GlusterFS disk image with the command:
+
+.. parsed-literal::
+
+ qemu-img create gluster://HOST/VOLUME/PATH SIZE
+
+Examples
+
+.. parsed-literal::
+
+ |qemu_system| -drive file=gluster://1.2.3.4/testvol/a.img
+ |qemu_system| -drive file=gluster+tcp://1.2.3.4/testvol/a.img
+ |qemu_system| -drive file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
+ |qemu_system| -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]/testvol/dir/a.img
+ |qemu_system| -drive
file=gluster+tcp://[1:2:3:4:5:6:7:8]:24007/testvol/dir/a.img
+ |qemu_system| -drive
file=gluster+tcp://server.domain.com:24007/testvol/dir/a.img
+ |qemu_system| -drive
file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
+ |qemu_system| -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img
+ |qemu_system| -drive
file=gluster://1.2.3.4/testvol/a.img,file.debug=9,file.logfile=/var/log/qemu-gluster.log
+ |qemu_system| 'json:{"driver":"qcow2",
+ "file":{"driver":"gluster",
+ "volume":"testvol","path":"a.img",
+
"debug":9,"logfile":"/var/log/qemu-gluster.log",
+
"server":[{"type":"tcp","host":"1.2.3.4","port":24007},
+
{"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
+ |qemu_system| -drive
driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
+
file.debug=9,file.logfile=/var/log/qemu-gluster.log,
+
file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
+
file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
+
+Secure Shell (ssh) disk images
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You can access disk images located on a remote ssh server
+by using the ssh protocol:
+
+.. parsed-literal::
+
+ |qemu_system| -drive
file=ssh://[USER@]SERVER[:PORT]/PATH[?host_key_check=HOST_KEY_CHECK]
+
+Alternative syntax using properties:
+
+.. parsed-literal::
+
+ |qemu_system| -drive
file.driver=ssh[,file.user=USER],file.host=SERVER[,file.port=PORT],file.path=PATH[,file.host_key_check=HOST_KEY_CHECK]
+
+*ssh* is the protocol.
+
+*USER* is the remote user. If not specified, then the local
+username is tried.
+
+*SERVER* specifies the remote ssh server. Any ssh server can be
+used, but it must implement the sftp-server protocol. Most Unix/Linux
+systems should work without requiring any extra configuration.
+
+*PORT* is the port number on which sshd is listening. By default
+the standard ssh port (22) is used.
+
+*PATH* is the path to the disk image.
+
+The optional *HOST_KEY_CHECK* parameter controls how the remote
+host's key is checked. The default is ``yes`` which means to use
+the local ``.ssh/known_hosts`` file. Setting this to ``no``
+turns off known-hosts checking. Or you can check that the host key
+matches a specific fingerprint:
+``host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8``
+(``sha1:`` can also be used as a prefix, but note that OpenSSH
+tools only use MD5 to print fingerprints).
+
+Currently authentication must be done using ssh-agent. Other
+authentication methods may be supported in future.
+
+Note: Many ssh servers do not support an ``fsync``-style operation.
+The ssh driver cannot guarantee that disk flush requests are
+obeyed, and this causes a risk of disk corruption if the remote
+server or network goes down during writes. The driver will
+print a warning when ``fsync`` is not supported:
+
+::
+
+ warning: ssh server ssh.example.com:22 does not support fsync
+
+With sufficiently new versions of libssh and OpenSSH, ``fsync`` is
+supported.
+
+NVMe disk images
+~~~~~~~~~~~~~~~~
+
+NVM Express (NVMe) storage controllers can be accessed directly by a userspace
+driver in QEMU. This bypasses the host kernel file system and block layers
+while retaining QEMU block layer functionalities, such as block jobs, I/O
+throttling, image formats, etc. Disk I/O performance is typically higher than
+with ``-drive file=/dev/sda`` using either thread pool or linux-aio.
+
+The controller will be exclusively used by the QEMU process once started. To be
+able to share storage between multiple VMs and other applications on the host,
+please use the file based protocols.
+
+Before starting QEMU, bind the host NVMe controller to the host vfio-pci
+driver. For example:
+
+.. parsed-literal::
+
+ # modprobe vfio-pci
+ # lspci -n -s 0000:06:0d.0
+ 06:0d.0 0401: 1102:0002 (rev 08)
+ # echo 0000:06:0d.0 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind
+ # echo 1102 0002 > /sys/bus/pci/drivers/vfio-pci/new_id
+
+ # |qemu_system| -drive file=nvme://HOST:BUS:SLOT.FUNC/NAMESPACE
+
+Alternative syntax using properties:
+
+.. parsed-literal::
+
+ |qemu_system| -drive
file.driver=nvme,file.device=HOST:BUS:SLOT.FUNC,file.namespace=NAMESPACE
+
+*HOST*:*BUS*:*SLOT*.\ *FUNC* is the NVMe controller's PCI device
+address on the host.
+
+*NAMESPACE* is the NVMe namespace number, starting from 1.
+
+Disk image file locking
+~~~~~~~~~~~~~~~~~~~~~~~
+
+By default, QEMU tries to protect image files from unexpected concurrent
+access, as long as it's supported by the block protocol driver and host
+operating system. If multiple QEMU processes (including QEMU emulators and
+utilities) try to open the same image with conflicting accessing modes, all but
+the first one will get an error.
+
+This feature is currently supported by the file protocol on Linux with the Open
+File Descriptor (OFD) locking API, and can be configured to fall back to POSIX
+locking if the POSIX host doesn't support Linux OFD locking.
+
+To explicitly enable image locking, specify "locking=on" in the file protocol
+driver options. If OFD locking is not possible, a warning will be printed and
+the POSIX locking API will be used. In this case there is a risk that the lock
+will get silently lost when doing hot plugging and block jobs, due to the
+shortcomings of the POSIX locking API.
+
+QEMU transparently handles lock handover during shared storage migration. For
+shared virtual disk images between multiple VMs, the "share-rw" device option
+should be used.
+
+By default, the guest has exclusive write access to its disk image. If the
+guest can safely share the disk image with other writers the
+``-device ...,share-rw=on`` parameter can be used. This is only safe if
+the guest is running software, such as a cluster file system, that
+coordinates disk accesses to avoid corruption.
+
+Note that share-rw=on only declares the guest's ability to share the disk.
+Some QEMU features, such as image file formats, require exclusive write access
+to the disk image and this is unaffected by the share-rw=on option.
+
+Alternatively, locking can be fully disabled by "locking=off" block device
+option. In the command line, the option is usually in the form of
+"file.locking=off" as the protocol driver is normally placed as a "file" child
+under a format driver. For example:
+
+::
+
+ -blockdev
driver=qcow2,file.filename=/path/to/image,file.locking=off,file.driver=file
+
+To check if image locking is active, check the output of the "lslocks" command
+on host and see if there are locks held by the QEMU process on the image file.
+More than one byte could be locked by the QEMU instance, each byte of which
+reflects a particular permission that is acquired or protected by the running
+block driver.
--
2.21.1
[PATCH 17/18] docs/system: convert the documentation of deprecated features to rST., Paolo Bonzini, 2020/02/26
[PATCH 05/18] qemu-doc: split qemu-doc.texi in multiple files, Paolo Bonzini, 2020/02/26
[PATCH 13/18] docs/system: put qemu-block-drivers body in an included file,
Paolo Bonzini <=
[PATCH 18/18] docs/system: convert Texinfo documentation to rST, Paolo Bonzini, 2020/02/26