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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
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10
qemu-img.c
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@@ -1375,7 +1375,6 @@ static int img_compare(int argc, char **argv)
for (;;) {
int64_t status1, status2;
BlockDriverState *file;
nb_sectors = sectors_to_process(total_sectors, sector_num);
if (nb_sectors <= 0) {
@@ -1383,7 +1382,7 @@ static int img_compare(int argc, char **argv)
}
status1 = bdrv_get_block_status_above(bs1, NULL, sector_num,
total_sectors1 - sector_num,
&pnum1, &file);
&pnum1, NULL);
if (status1 < 0) {
ret = 3;
error_report("Sector allocation test failed for %s", filename1);
@@ -1393,7 +1392,7 @@ static int img_compare(int argc, char **argv)
status2 = bdrv_get_block_status_above(bs2, NULL, sector_num,
total_sectors2 - sector_num,
&pnum2, &file);
&pnum2, NULL);
if (status2 < 0) {
ret = 3;
error_report("Sector allocation test failed for %s", filename2);
@@ -1599,15 +1598,14 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
n = MIN(s->total_sectors - sector_num, BDRV_REQUEST_MAX_SECTORS);
if (s->sector_next_status <= sector_num) {
BlockDriverState *file;
if (s->target_has_backing) {
ret = bdrv_get_block_status(blk_bs(s->src[src_cur]),
sector_num - src_cur_offset,
n, &n, &file);
n, &n, NULL);
} else {
ret = bdrv_get_block_status_above(blk_bs(s->src[src_cur]), NULL,
sector_num - src_cur_offset,
n, &n, &file);
n, &n, NULL);
}
if (ret < 0) {
return ret;