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Re: [Qemu-devel] [PATCH v2 2/6] block: Convert .bdrv_truncate callback t
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v2 2/6] block: Convert .bdrv_truncate callback to coroutine_fn |
Date: |
Wed, 27 Jun 2018 12:54:58 +0100 |
User-agent: |
Mutt/1.10.0 (2018-05-17) |
On Tue, Jun 26, 2018 at 04:24:30PM +0200, Kevin Wolf wrote:
> bdrv_truncate() is an operation that can block (even for a quite long
> time, depending on the PreallocMode) in I/O paths that shouldn't block.
> Convert it to a coroutine_fn so that we have the infrastructure for
> drivers to make their .bdrv_co_truncate implementation asynchronous.
>
> This change could potentially introduce new race conditions because
> bdrv_truncate() isn't necessarily executed atomically any more. Whether
> this is a problem needs to be evaluated for each block driver that
> supports truncate:
>
> * file-posix/win32, gluster, iscsi, nfs, rbd, ssh, sheepdog: The
> protocol drivers are trivially safe because they don't actually yield
> yet, so there is no change in behaviour.
>
> * copy-on-read, crypto, raw-format: Essentially just filter drivers that
> pass the request to a child node, no problem.
>
> * qcow2: The implementation modifies metadata, so it needs to hold
> s->lock to be safe with concurrent I/O requests. In order to avoid
> double locking, this requires pulling the locking out into
> preallocate_co() and using qcow2_write_caches() instead of
> bdrv_flush().
>
> * qed: Does a single header update, this is fine without locking.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> include/block/block.h | 4 +++
> include/block/block_int.h | 4 +--
> block.c | 63 ++++++++++++++++++++++++++++++++++------
> block/copy-on-read.c | 8 +++---
> block/crypto.c | 9 +++---
> block/file-posix.c | 12 ++++----
> block/file-win32.c | 6 ++--
> block/gluster.c | 14 +++++----
> block/iscsi.c | 8 +++---
> block/nfs.c | 7 +++--
> block/qcow2.c | 73
> ++++++++++++++++++++++++++++-------------------
> block/qed.c | 8 ++++--
> block/raw-format.c | 8 +++---
> block/rbd.c | 8 ++++--
> block/sheepdog.c | 12 ++++----
> block/ssh.c | 6 ++--
> 16 files changed, 161 insertions(+), 89 deletions(-)
Reviewed-by: Stefan Hajnoczi <address@hidden>
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- Re: [Qemu-devel] [PATCH v2 1/6] qcow2: Fix qcow2_truncate() error return value, (continued)
- [Qemu-devel] [PATCH v2 3/6] qcow2: Remove coroutine trampoline for preallocate_co(), Kevin Wolf, 2018/06/26
- [Qemu-devel] [PATCH v2 4/6] block: Move bdrv_truncate() implementation to io.c, Kevin Wolf, 2018/06/26
- [Qemu-devel] [PATCH v2 5/6] block: Use tracked request for truncate, Kevin Wolf, 2018/06/26
- [Qemu-devel] [PATCH v2 6/6] file-posix: Make .bdrv_co_truncate asynchronous, Kevin Wolf, 2018/06/26
- [Qemu-devel] [PATCH v2 2/6] block: Convert .bdrv_truncate callback to coroutine_fn, Kevin Wolf, 2018/06/26
- Re: [Qemu-devel] [PATCH v2 2/6] block: Convert .bdrv_truncate callback to coroutine_fn,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCH v2 0/6] file-posix: Make truncate/preallocate asynchronous, Stefan Hajnoczi, 2018/06/27