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qed: Simplify backing reads

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The other four drivers that support backing files (qcow, qcow2,
parallels, vmdk) all rely on the block layer to populate zeroes when
reading beyond EOF of a short backing file.  We can simplify the qed
code by doing likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200528094405.145708-11-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Eric Blake 2020-05-28 12:44:05 +03:00 committed by Max Reitz
parent a2adbbf603
commit 365fed5111
2 changed files with 6 additions and 59 deletions
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62
block/qed.c
View File

@ -849,56 +849,18 @@ static BDRVQEDState *acb_to_s(QEDAIOCB *acb)
* @s: QED state
* @pos: Byte position in device
* @qiov: Destination I/O vector
* @backing_qiov: Possibly shortened copy of qiov, to be allocated here
* @cb: Completion function
* @opaque: User data for completion function
*
* This function reads qiov->size bytes starting at pos from the backing file.
* If there is no backing file then zeroes are read.
*/
static int coroutine_fn qed_read_backing_file(BDRVQEDState *s, uint64_t pos,
QEMUIOVector *qiov,
QEMUIOVector **backing_qiov)
QEMUIOVector *qiov)
{
uint64_t backing_length = 0;
size_t size;
int ret;
/* If there is a backing file, get its length. Treat the absence of a
* backing file like a zero length backing file.
*/
if (s->bs->backing) {
int64_t l = bdrv_getlength(s->bs->backing->bs);
if (l < 0) {
return l;
}
backing_length = l;
}
/* Zero all sectors if reading beyond the end of the backing file */
if (pos >= backing_length ||
pos + qiov->size > backing_length) {
qemu_iovec_memset(qiov, 0, 0, qiov->size);
}
/* Complete now if there are no backing file sectors to read */
if (pos >= backing_length) {
return 0;
}
/* If the read straddles the end of the backing file, shorten it */
size = MIN((uint64_t)backing_length - pos, qiov->size);
assert(*backing_qiov == NULL);
*backing_qiov = g_new(QEMUIOVector, 1);
qemu_iovec_init(*backing_qiov, qiov->niov);
qemu_iovec_concat(*backing_qiov, qiov, 0, size);
BLKDBG_EVENT(s->bs->file, BLKDBG_READ_BACKING_AIO);
ret = bdrv_co_preadv(s->bs->backing, pos, size, *backing_qiov, 0);
if (ret < 0) {
return ret;
return bdrv_co_preadv(s->bs->backing, pos, qiov->size, qiov, 0);
}
qemu_iovec_memset(qiov, 0, 0, qiov->size);
return 0;
}
@ -915,7 +877,6 @@ static int coroutine_fn qed_copy_from_backing_file(BDRVQEDState *s,
uint64_t offset)
{
QEMUIOVector qiov;
QEMUIOVector *backing_qiov = NULL;
int ret;
/* Skip copy entirely if there is no work to do */
@ -925,13 +886,7 @@ static int coroutine_fn qed_copy_from_backing_file(BDRVQEDState *s,
qemu_iovec_init_buf(&qiov, qemu_blockalign(s->bs, len), len);
ret = qed_read_backing_file(s, pos, &qiov, &backing_qiov);
if (backing_qiov) {
qemu_iovec_destroy(backing_qiov);
g_free(backing_qiov);
backing_qiov = NULL;
}
ret = qed_read_backing_file(s, pos, &qiov);
if (ret) {
goto out;
@ -1339,8 +1294,7 @@ static int coroutine_fn qed_aio_read_data(void *opaque, int ret,
qemu_iovec_memset(&acb->cur_qiov, 0, 0, acb->cur_qiov.size);
r = 0;
} else if (ret != QED_CLUSTER_FOUND) {
r = qed_read_backing_file(s, acb->cur_pos, &acb->cur_qiov,
&acb->backing_qiov);
r = qed_read_backing_file(s, acb->cur_pos, &acb->cur_qiov);
} else {
BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
r = bdrv_co_preadv(bs->file, offset, acb->cur_qiov.size,
@ -1365,12 +1319,6 @@ static int coroutine_fn qed_aio_next_io(QEDAIOCB *acb)
while (1) {
trace_qed_aio_next_io(s, acb, 0, acb->cur_pos + acb->cur_qiov.size);
if (acb->backing_qiov) {
qemu_iovec_destroy(acb->backing_qiov);
g_free(acb->backing_qiov);
acb->backing_qiov = NULL;
}
acb->qiov_offset += acb->cur_qiov.size;
acb->cur_pos += acb->cur_qiov.size;
qemu_iovec_reset(&acb->cur_qiov);

1
block/qed.h
View File

@ -140,7 +140,6 @@ typedef struct QEDAIOCB {
/* Current cluster scatter-gather list */
QEMUIOVector cur_qiov;
QEMUIOVector *backing_qiov;
uint64_t cur_pos; /* position on block device, in bytes */
uint64_t cur_cluster; /* cluster offset in image file */
unsigned int cur_nclusters; /* number of clusters being accessed */