[Qemu-devel] [RFC PATCH 0/5] Make discard visible to the guests

[Paolo Bonzini]

The major missing step in order to implement thin provisioning is
exposing discard commands to the guest.  This series implements
minimal control of this capability.

Whether to enable discard or not is made a host parameter, so that
choices in storage technology do not affect the hardware that the
guest sees.  While it is still possible to fine-tune the parameters
(at least for SCSI disks), the default granularity is set to the
logical block size or 4k, whichever is largest, because cluster
sizes below 4k are rarely used and 4K is a typical block size
for files.

Nevertheless, using DISCARD with filesystems can cause very severe
fragmentation, so it is left default-off for now.  This can change later
when we implement the "anchor" operation for efficient management of
preallocated files.

Paolo


Paolo Bonzini (5):
  block: implement BDRV_O_UNMAP
  blockdev: add discard suboption to -drive
  qemu-nbd: add --discard option
  blockdev: enable discard by default
  pc: add compatibility machine types for 1.4

 block.c               | 25 +++++++++++++++++++++++++
 blockdev.c            | 11 +++++++++++
 hw/block-common.h     |  2 +-
 hw/ide/qdev.c         |  5 ++++-
 hw/pc.h               | 32 ++++++++++++++++++++++++++++++++
 hw/pc_piix.c          | 18 ++++++++++++++++--
 hw/pc_q35.c           | 19 ++++++++++++++++---
 hw/scsi-disk.c        | 13 ++++++++++---
 include/block/block.h |  2 ++
 qemu-io.c             | 11 +++++++++--
 qemu-nbd.c            | 18 +++++++++++++++---
 qemu-nbd.texi         |  4 ++++
 qemu-options.hx       |  2 ++
 13 files changed, 147 insertions(+), 15 deletions(-)

-- 
1.8.1.2