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block: make copy-on-read a per-request flag
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Previously copy-on-read could only be enabled for all requests to a
block device.  This means requests coming from the guest as well as
QEMU's internal requests would perform copy-on-read when enabled.

For image streaming we want to support finer-grained behavior than just
populating the image file from its backing image.  Image streaming
supports partial streaming where a common backing image is preserved.
In this case guest requests should not perform copy-on-read because they
would indiscriminately copy data which should be left in a backing image
from the backing chain.

Introduce a per-request flag for copy-on-read so that a block device can
process both regular and copy-on-read requests.  Overlapping reads and
writes still need to be serialized for correctness when copy-on-read is
happening, so add an in-flight reference count to track this.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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@kevmw
Stefan Hajnoczi authored and kevmw committed Jan 26, 2012
1 parent 2d3735d commit 470c050
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Showing 4 changed files with 45 additions and 12 deletions.
49 changes: 38 additions & 11 deletions block.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,10 @@

#define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */

typedef enum {
BDRV_REQ_COPY_ON_READ = 0x1,
} BdrvRequestFlags;

static void bdrv_dev_change_media_cb(BlockDriverState *bs, bool load);
static BlockDriverAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
Expand All @@ -62,7 +66,8 @@ static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *iov);
static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
BdrvRequestFlags flags);
static int coroutine_fn bdrv_co_do_writev(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
static BlockDriverAIOCB *bdrv_co_aio_rw_vector(BlockDriverState *bs,
Expand Down Expand Up @@ -1292,7 +1297,7 @@ static void coroutine_fn bdrv_rw_co_entry(void *opaque)

if (!rwco->is_write) {
rwco->ret = bdrv_co_do_readv(rwco->bs, rwco->sector_num,
rwco->nb_sectors, rwco->qiov);
rwco->nb_sectors, rwco->qiov, 0);
} else {
rwco->ret = bdrv_co_do_writev(rwco->bs, rwco->sector_num,
rwco->nb_sectors, rwco->qiov);
Expand Down Expand Up @@ -1500,7 +1505,7 @@ int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset,
return 0;
}

static int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
{
/* Perform I/O through a temporary buffer so that users who scribble over
Expand All @@ -1523,8 +1528,8 @@ static int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
round_to_clusters(bs, sector_num, nb_sectors,
&cluster_sector_num, &cluster_nb_sectors);

trace_bdrv_co_copy_on_readv(bs, sector_num, nb_sectors,
cluster_sector_num, cluster_nb_sectors);
trace_bdrv_co_do_copy_on_readv(bs, sector_num, nb_sectors,
cluster_sector_num, cluster_nb_sectors);

iov.iov_len = cluster_nb_sectors * BDRV_SECTOR_SIZE;
iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len);
Expand Down Expand Up @@ -1559,7 +1564,8 @@ static int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
* Handle a read request in coroutine context
*/
static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
BdrvRequestFlags flags)
{
BlockDriver *drv = bs->drv;
BdrvTrackedRequest req;
Expand All @@ -1578,12 +1584,19 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
}

if (bs->copy_on_read) {
flags |= BDRV_REQ_COPY_ON_READ;
}
if (flags & BDRV_REQ_COPY_ON_READ) {
bs->copy_on_read_in_flight++;
}

if (bs->copy_on_read_in_flight) {
wait_for_overlapping_requests(bs, sector_num, nb_sectors);
}

tracked_request_begin(&req, bs, sector_num, nb_sectors, false);

if (bs->copy_on_read) {
if (flags & BDRV_REQ_COPY_ON_READ) {
int pnum;

ret = bdrv_co_is_allocated(bs, sector_num, nb_sectors, &pnum);
Expand All @@ -1592,7 +1605,7 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
}

if (!ret || pnum != nb_sectors) {
ret = bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, qiov);
ret = bdrv_co_do_copy_on_readv(bs, sector_num, nb_sectors, qiov);
goto out;
}
}
Expand All @@ -1601,6 +1614,11 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,

out:
tracked_request_end(&req);

if (flags & BDRV_REQ_COPY_ON_READ) {
bs->copy_on_read_in_flight--;
}

return ret;
}

Expand All @@ -1609,7 +1627,16 @@ int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,
{
trace_bdrv_co_readv(bs, sector_num, nb_sectors);

return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov);
return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov, 0);
}

int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
{
trace_bdrv_co_copy_on_readv(bs, sector_num, nb_sectors);

return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov,
BDRV_REQ_COPY_ON_READ);
}

/*
Expand Down Expand Up @@ -1637,7 +1664,7 @@ static int coroutine_fn bdrv_co_do_writev(BlockDriverState *bs,
bdrv_io_limits_intercept(bs, true, nb_sectors);
}

if (bs->copy_on_read) {
if (bs->copy_on_read_in_flight) {
wait_for_overlapping_requests(bs, sector_num, nb_sectors);
}

Expand Down Expand Up @@ -3144,7 +3171,7 @@ static void coroutine_fn bdrv_co_do_rw(void *opaque)

if (!acb->is_write) {
acb->req.error = bdrv_co_do_readv(bs, acb->req.sector,
acb->req.nb_sectors, acb->req.qiov);
acb->req.nb_sectors, acb->req.qiov, 0);
} else {
acb->req.error = bdrv_co_do_writev(bs, acb->req.sector,
acb->req.nb_sectors, acb->req.qiov);
Expand Down
2 changes: 2 additions & 0 deletions block.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,8 @@ int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset,
const void *buf, int count);
int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,
int nb_sectors, QEMUIOVector *qiov);
int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
int coroutine_fn bdrv_co_writev(BlockDriverState *bs, int64_t sector_num,
int nb_sectors, QEMUIOVector *qiov);
int coroutine_fn bdrv_co_is_allocated(BlockDriverState *bs, int64_t sector_num,
Expand Down
3 changes: 3 additions & 0 deletions block_int.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -218,6 +218,9 @@ struct BlockDriverState {
BlockDriverState *backing_hd;
BlockDriverState *file;

/* number of in-flight copy-on-read requests */
unsigned int copy_on_read_in_flight;

/* async read/write emulation */

void *sync_aiocb;
Expand Down
3 changes: 2 additions & 1 deletion trace-events
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,9 +65,10 @@ bdrv_aio_readv(void *bs, int64_t sector_num, int nb_sectors, void *opaque) "bs %
bdrv_aio_writev(void *bs, int64_t sector_num, int nb_sectors, void *opaque) "bs %p sector_num %"PRId64" nb_sectors %d opaque %p"
bdrv_lock_medium(void *bs, bool locked) "bs %p locked %d"
bdrv_co_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
bdrv_co_copy_on_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
bdrv_co_writev(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
bdrv_co_io_em(void *bs, int64_t sector_num, int nb_sectors, int is_write, void *acb) "bs %p sector_num %"PRId64" nb_sectors %d is_write %d acb %p"
bdrv_co_copy_on_readv(void *bs, int64_t sector_num, int nb_sectors, int64_t cluster_sector_num, int cluster_nb_sectors) "bs %p sector_num %"PRId64" nb_sectors %d cluster_sector_num %"PRId64" cluster_nb_sectors %d"
bdrv_co_do_copy_on_readv(void *bs, int64_t sector_num, int nb_sectors, int64_t cluster_sector_num, int cluster_nb_sectors) "bs %p sector_num %"PRId64" nb_sectors %d cluster_sector_num %"PRId64" cluster_nb_sectors %d"

# hw/virtio-blk.c
virtio_blk_req_complete(void *req, int status) "req %p status %d"
Expand Down

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