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Re: [Qemu-block] [PATCH v4 03/15] block: introduce BDRV_REQ_ALLOCATE fla
From: |
Eric Blake |
Subject: |
Re: [Qemu-block] [PATCH v4 03/15] block: introduce BDRV_REQ_ALLOCATE flag |
Date: |
Fri, 4 Aug 2017 14:51:34 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 08/01/2017 09:19 AM, Anton Nefedov wrote:
> The flag is supposed to indicate that the region of the disk image has
> to be sufficiently allocated so it reads as zeroes. The call with the flag
> set has to return -ENOTSUP if allocation cannot be done efficiently
> (i.e. without falling back to writing actual buffers)
>
> Signed-off-by: Anton Nefedov <address@hidden>
> ---
> include/block/block.h | 6 +++++-
> include/block/block_int.h | 2 +-
> block/io.c | 20 +++++++++++++++++---
> 3 files changed, 23 insertions(+), 5 deletions(-)
Reviewed-by: Eric Blake <address@hidden>
You might want the commit message to be a bit more verbose...
>
> diff --git a/include/block/block.h b/include/block/block.h
> index 7fe0125..828da67 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -65,9 +65,13 @@ typedef enum {
> BDRV_REQ_NO_SERIALISING = 0x8,
> BDRV_REQ_FUA = 0x10,
> BDRV_REQ_WRITE_COMPRESSED = 0x20,
> + /* The BDRV_REQ_ALLOCATE flag is used to indicate that the driver has to
> + * efficiently allocate the space so it reads as zeroes, or return an
> error.
> + */
> + BDRV_REQ_ALLOCATE = 0x40,
>
> /* Mask of valid flags */
> - BDRV_REQ_MASK = 0x3f,
> + BDRV_REQ_MASK = 0x7f,
> } BdrvRequestFlags;
>
> typedef struct BlockSizes {
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 9b94b32..9b64411 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -585,7 +585,7 @@ struct BlockDriverState {
> /* Flags honored during pwrite (so far: BDRV_REQ_FUA) */
> unsigned int supported_write_flags;
> /* Flags honored during pwrite_zeroes (so far: BDRV_REQ_FUA,
> - * BDRV_REQ_MAY_UNMAP) */
> + * BDRV_REQ_MAY_UNMAP, BDRV_REQ_ALLOCATE) */
> unsigned int supported_zero_flags;
...in addition to adding the new flag here and documenting its semantics
for drivers...
>
> /* the following member gives a name to every node on the bs graph. */
> diff --git a/block/io.c b/block/io.c
> index 375fc66..04d495e 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1245,7 +1245,7 @@ static int coroutine_fn
> bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
> assert(!bs->supported_zero_flags);
> }
>
> - if (ret == -ENOTSUP) {
> + if (ret == -ENOTSUP && !(flags & BDRV_REQ_ALLOCATE)) {
> /* Fall back to bounce buffer if write zeroes is unsupported */
> BdrvRequestFlags write_flags = flags & ~BDRV_REQ_ZERO_WRITE;
...you also made sure that anywhere the flag is in use you avoid a slow
fallback...
> @@ -1639,6 +1645,14 @@ int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild
> *child, int64_t offset,
> {
> trace_bdrv_co_pwrite_zeroes(child->bs, offset, bytes, flags);
>
> + assert(!(flags & BDRV_REQ_MAY_UNMAP && flags & BDRV_REQ_ALLOCATE));
> +
> + if (flags & BDRV_REQ_ALLOCATE &&
> + !(child->bs->supported_zero_flags & BDRV_REQ_ALLOCATE))
> + {
> + return -ENOTSUP;
...as well as providing a sane default to make the flag always trigger
-ENOTSUP until individual drivers implement something in later patches.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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- [Qemu-block] [PATCH v4 04/15] block: treat BDRV_REQ_ALLOCATE as serialising, (continued)
- [Qemu-block] [PATCH v4 04/15] block: treat BDRV_REQ_ALLOCATE as serialising, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 05/15] file-posix: support BDRV_REQ_ALLOCATE, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 06/15] block: support BDRV_REQ_ALLOCATE in passthrough drivers, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 09/15] qcow2: truncate preallocated space, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 02/15] blkverify: set supported write/zero flags, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 03/15] block: introduce BDRV_REQ_ALLOCATE flag, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 11/15] qcow2: move is_zero() up, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 12/15] qcow2: skip writing zero buffers to empty COW areas, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 14/15] iotest 190: test BDRV_REQ_ALLOCATE, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 13/15] qcow2: allocate image space by-cluster, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 15/15] iotest 134: test cluster-misaligned encrypted write, Anton Nefedov, 2017/08/01
- [Qemu-block] [PATCH v4 10/15] qcow2: check space leak at the end of the image, Anton Nefedov, 2017/08/01