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null: Switch to byte-based read/write 

We are gradually moving away from sector-based interfaces, towards
byte-based.  Make the change for the last few sector-based callbacks
in the null-co and null-aio drivers.

Note that since the null driver does nothing on writes, it trivially
supports the BDRV_REQ_FUA flag (all writes have already landed to
the same bit-bucket without needing an extra flush call).  Also, since
the null driver does just as well with byte-based requests, we can
now avoid cycles wasted on read-modify-write by taking advantage of
the block layer now defaulting the alignment to 1 instead of 512.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2018-04-24 14:25:03 -05:00 committed by Kevin Wolf
parent de7056a3f9
commit b3241e9274
1 changed files with 23 additions and 22 deletions
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45
block/null.c
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@ -93,6 +93,7 @@ static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
}
s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
qemu_opts_del(opts);
bs->supported_write_flags = BDRV_REQ_FUA;
return ret;
}
@ -116,22 +117,22 @@ static coroutine_fn int null_co_common(BlockDriverState *bs)
return 0;
}
static coroutine_fn int null_co_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
static coroutine_fn int null_co_preadv(BlockDriverState *bs,
uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
BDRVNullState *s = bs->opaque;
if (s->read_zeroes) {
qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
qemu_iovec_memset(qiov, 0, 0, bytes);
}
return null_co_common(bs);
}
static coroutine_fn int null_co_writev(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
static coroutine_fn int null_co_pwritev(BlockDriverState *bs,
uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
return null_co_common(bs);
}
@ -186,26 +187,26 @@ static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
return &acb->common;
}
static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
int64_t sector_num, QEMUIOVector *qiov,
int nb_sectors,
BlockCompletionFunc *cb,
void *opaque)
static BlockAIOCB *null_aio_preadv(BlockDriverState *bs,
uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags,
BlockCompletionFunc *cb,
void *opaque)
{
BDRVNullState *s = bs->opaque;
if (s->read_zeroes) {
qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
qemu_iovec_memset(qiov, 0, 0, bytes);
}
return null_aio_common(bs, cb, opaque);
}
static BlockAIOCB *null_aio_writev(BlockDriverState *bs,
int64_t sector_num, QEMUIOVector *qiov,
int nb_sectors,
BlockCompletionFunc *cb,
void *opaque)
static BlockAIOCB *null_aio_pwritev(BlockDriverState *bs,
uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags,
BlockCompletionFunc *cb,
void *opaque)
{
return null_aio_common(bs, cb, opaque);
}
@ -265,8 +266,8 @@ static BlockDriver bdrv_null_co = {
.bdrv_close = null_close,
.bdrv_getlength = null_getlength,
.bdrv_co_readv = null_co_readv,
.bdrv_co_writev = null_co_writev,
.bdrv_co_preadv = null_co_preadv,
.bdrv_co_pwritev = null_co_pwritev,
.bdrv_co_flush_to_disk = null_co_flush,
.bdrv_reopen_prepare = null_reopen_prepare,
@ -285,8 +286,8 @@ static BlockDriver bdrv_null_aio = {
.bdrv_close = null_close,
.bdrv_getlength = null_getlength,
.bdrv_aio_readv = null_aio_readv,
.bdrv_aio_writev = null_aio_writev,
.bdrv_aio_preadv = null_aio_preadv,
.bdrv_aio_pwritev = null_aio_pwritev,
.bdrv_aio_flush = null_aio_flush,
.bdrv_reopen_prepare = null_reopen_prepare,