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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
include/block/block_int.h
View file

@ -202,10 +202,12 @@ struct BlockDriver {
int64_t offset, int bytes);
/*
* Building block for bdrv_block_status[_above]. The driver should
* answer only according to the current layer, and should not
* set BDRV_BLOCK_ALLOCATED, but may set BDRV_BLOCK_RAW. See block.h
* for the meaning of _DATA, _ZERO, and _OFFSET_VALID.
* Building block for bdrv_block_status[_above] and
* bdrv_is_allocated[_above]. The driver should answer only
* according to the current layer, and should not set
* BDRV_BLOCK_ALLOCATED, but may set BDRV_BLOCK_RAW. See block.h
* for the meaning of _DATA, _ZERO, and _OFFSET_VALID. The block
* layer guarantees non-NULL pnum and file.
*/
int64_t coroutine_fn (*bdrv_co_get_block_status)(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, int *pnum,