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block: implement BDRV_REQ_PREFETCH

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Do effective copy-on-read request when we don't need data actually. It
will be used for block-stream and NBD_CMD_CACHE.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20190725100550.33801-2-vsementsov@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
[eblake: comment grammar fix]
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2019-07-25 13:05:48 +03:00 committed by Eric Blake
parent aec21d3175
commit 3299e5ecf7
2 changed files with 19 additions and 7 deletions
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18
block/io.c
View File

@ -1167,7 +1167,8 @@ bdrv_driver_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
}
static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
int64_t offset, unsigned int bytes, QEMUIOVector *qiov)
int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
int flags)
{
BlockDriverState *bs = child->bs;
@ -1278,9 +1279,11 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
goto err;
}
qemu_iovec_from_buf(qiov, progress, bounce_buffer + skip_bytes,
pnum - skip_bytes);
} else {
if (!(flags & BDRV_REQ_PREFETCH)) {
qemu_iovec_from_buf(qiov, progress, bounce_buffer + skip_bytes,
pnum - skip_bytes);
}
} else if (!(flags & BDRV_REQ_PREFETCH)) {
/* Read directly into the destination */
qemu_iovec_init(&local_qiov, qiov->niov);
qemu_iovec_concat(&local_qiov, qiov, progress, pnum - skip_bytes);
@ -1331,7 +1334,8 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
* potential fallback support, if we ever implement any read flags
* to pass through to drivers. For now, there aren't any
* passthrough flags. */
assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ)));
assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ |
BDRV_REQ_PREFETCH)));
/* Handle Copy on Read and associated serialisation */
if (flags & BDRV_REQ_COPY_ON_READ) {
@ -1359,7 +1363,9 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
}
if (!ret || pnum != bytes) {
ret = bdrv_co_do_copy_on_readv(child, offset, bytes, qiov);
ret = bdrv_co_do_copy_on_readv(child, offset, bytes, qiov, flags);
goto out;
} else if (flags & BDRV_REQ_PREFETCH) {
goto out;
}
}

8
include/block/block.h
View File

@ -88,8 +88,14 @@ typedef enum {
* fallback. */
BDRV_REQ_NO_FALLBACK = 0x100,
/*
* BDRV_REQ_PREFETCH may be used only together with BDRV_REQ_COPY_ON_READ
* on read request and means that caller doesn't really need data to be
* written to qiov parameter which may be NULL.
*/
BDRV_REQ_PREFETCH = 0x200,
/* Mask of valid flags */
BDRV_REQ_MASK = 0x1ff,
BDRV_REQ_MASK = 0x3ff,
} BdrvRequestFlags;
typedef struct BlockSizes {