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block: Fix documentation for BDRV_REQ_MAY_UNMAP

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BDRV_REQ_MAY_UNMAP in a write_zeroes request does not only allow the
driver to unmap the blocks, but it actively requests that the blocks be
unmapped afterwards if at all possible.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2018-07-25 13:20:32 +02:00
parent 8ba4f10fa6
commit 52ebcb2682
1 changed files with 6 additions and 5 deletions
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11
include/block/block.h
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@ -43,11 +43,12 @@ typedef struct BlockFragInfo {
typedef enum {
BDRV_REQ_COPY_ON_READ = 0x1,
BDRV_REQ_ZERO_WRITE = 0x2,
/* The BDRV_REQ_MAY_UNMAP flag is used to indicate that the block driver
* is allowed to optimize a write zeroes request by unmapping (discarding)
* blocks if it is guaranteed that the result will read back as
* zeroes. The flag is only passed to the driver if the block device is
* opened with BDRV_O_UNMAP.
/*
* The BDRV_REQ_MAY_UNMAP flag is used in write_zeroes requests to indicate
* that the block driver should unmap (discard) blocks if it is guaranteed
* that the result will read back as zeroes. The flag is only passed to the
* driver if the block device is opened with BDRV_O_UNMAP.
*/
BDRV_REQ_MAY_UNMAP = 0x4,