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qed: add .bdrv_co_write_zeroes() support

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Zero writes are a dedicated interface for writing regions of zeroes into
the image file.  If clusters are not yet allocated it is possible to use
an efficient metadata representation which keeps the image file compact
and does not store individual zero bytes.

Implementing this for the QED image format is fairly straightforward.
The only issue is that when a zero write touches an existing cluster we
have to allocate a bounce buffer and perform a regular write.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2012-02-07 13:27:28 +00:00 • committed by Kevin Wolf
parent 6e4f59bd0d
commit 0e71be1932
2 changed files with 103 additions and 8 deletions
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block/qed.h
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@ -125,6 +125,7 @@ typedef struct QEDRequest {
enum {
QED_AIOCB_WRITE = 0x0001, /* read or write? */
QED_AIOCB_ZERO = 0x0002, /* zero write, used with QED_AIOCB_WRITE */
};
typedef struct QEDAIOCB {