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block: Allow NULL file for bdrv_get_block_status()

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Not all callers care about which BDS owns the mapping for a given
range of the file.  This patch merely simplifies the callers by
consolidating the logic in the common call point, while guaranteeing
a non-NULL file to all the driver callbacks, for no semantic change.
The only caller that does not care about pnum is bdrv_is_allocated,
as invoked by vvfat; we can likewise add assertions that the rest
of the stack does not have to worry about a NULL pnum.

Furthermore, this will also set the stage for a future cleanup: when
a caller does not care about which BDS owns an offset, it would be
nice to allow the driver to optimize things to not have to return
BDRV_BLOCK_OFFSET_VALID in the first place.  In the case of fragmented
allocation (for example, it's fairly easy to create a qcow2 image
where consecutive guest addresses are not at consecutive host
addresses), the current contract requires bdrv_get_block_status()
to clamp *pnum to the limit where host addresses are no longer
consecutive, but allowing a NULL file means that *pnum could be
set to the full length of known-allocated data.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2017-10-11 22:46:57 -05:00 • committed by Kevin Wolf
parent 760c4d43ae
commit 298a1665a2
5 changed files with 40 additions and 40 deletions
Download patch file Download diff file Expand all files Collapse all files

49
block/io.c
View file

@ -718,7 +718,6 @@ int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags)
{
int64_t target_sectors, ret, nb_sectors, sector_num = 0;
BlockDriverState *bs = child->bs;
BlockDriverState *file;
int n;
target_sectors = bdrv_nb_sectors(bs);
@ -731,7 +730,7 @@ int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags)
if (nb_sectors <= 0) {
return 0;
}
ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n, &file);
ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n, NULL);
if (ret < 0) {
error_report("error getting block status at sector %" PRId64 ": %s",
sector_num, strerror(-ret));
@ -1820,8 +1819,9 @@ int64_t coroutine_fn bdrv_co_get_block_status_from_backing(BlockDriverState *bs,
* beyond the end of the disk image it will be clamped; if 'pnum' is set to
* the end of the image, then the returned value will include BDRV_BLOCK_EOF.
*
* If returned value is positive and BDRV_BLOCK_OFFSET_VALID bit is set, 'file'
* points to the BDS which the sector range is allocated in.
* If returned value is positive, BDRV_BLOCK_OFFSET_VALID bit is set, and
* 'file' is non-NULL, then '*file' points to the BDS which the sector range
* is allocated in.
*/
static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
int64_t sector_num,
@ -1831,20 +1831,23 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
int64_t total_sectors;
int64_t n;
int64_t ret, ret2;
BlockDriverState *local_file = NULL;
*file = NULL;
assert(pnum);
*pnum = 0;
total_sectors = bdrv_nb_sectors(bs);
if (total_sectors < 0) {
return total_sectors;
ret = total_sectors;
goto early_out;
}
if (sector_num >= total_sectors) {
*pnum = 0;
return BDRV_BLOCK_EOF;
ret = BDRV_BLOCK_EOF;
goto early_out;
}
if (!nb_sectors) {
*pnum = 0;
return 0;
ret = 0;
goto early_out;
}
n = total_sectors - sector_num;
@ -1860,23 +1863,23 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
}
if (bs->drv->protocol_name) {
ret |= BDRV_BLOCK_OFFSET_VALID | (sector_num * BDRV_SECTOR_SIZE);
*file = bs;
local_file = bs;
}
return ret;
goto early_out;
}
bdrv_inc_in_flight(bs);
ret = bs->drv->bdrv_co_get_block_status(bs, sector_num, nb_sectors, pnum,
file);
&local_file);
if (ret < 0) {
*pnum = 0;
goto out;
}
if (ret & BDRV_BLOCK_RAW) {
assert(ret & BDRV_BLOCK_OFFSET_VALID && *file);
ret = bdrv_co_get_block_status(*file, ret >> BDRV_SECTOR_BITS,
*pnum, pnum, file);
assert(ret & BDRV_BLOCK_OFFSET_VALID && local_file);
ret = bdrv_co_get_block_status(local_file, ret >> BDRV_SECTOR_BITS,
*pnum, pnum, &local_file);
goto out;
}
@ -1894,14 +1897,13 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
}
}
if (*file && *file != bs &&
if (local_file && local_file != bs &&
(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO) &&
(ret & BDRV_BLOCK_OFFSET_VALID)) {
BlockDriverState *file2;
int file_pnum;
ret2 = bdrv_co_get_block_status(*file, ret >> BDRV_SECTOR_BITS,
*pnum, &file_pnum, &file2);
ret2 = bdrv_co_get_block_status(local_file, ret >> BDRV_SECTOR_BITS,
*pnum, &file_pnum, NULL);
if (ret2 >= 0) {
/* Ignore errors. This is just providing extra information, it
* is useful but not necessary.
@ -1927,6 +1929,10 @@ out:
if (ret >= 0 && sector_num + *pnum == total_sectors) {
ret |= BDRV_BLOCK_EOF;
}
early_out:
if (file) {
*file = local_file;
}
return ret;
}
@ -2026,7 +2032,6 @@ int64_t bdrv_get_block_status(BlockDriverState *bs,
int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
int64_t bytes, int64_t *pnum)
{
BlockDriverState *file;
int64_t sector_num = offset >> BDRV_SECTOR_BITS;
int nb_sectors = bytes >> BDRV_SECTOR_BITS;
int64_t ret;
@ -2035,7 +2040,7 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE) && bytes < INT_MAX);
ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &psectors,
&file);
NULL);
if (ret < 0) {
return ret;
}