Add 'discard' request handling
Some block devices benefit from a hint that they can forget the contents
of certain sectors. Add basic support for this to the block core, along
with a 'blkdev_issue_discard()' helper function which issues such
requests.
The caller doesn't get to provide an end_io functio, since
blkdev_issue_discard() will automatically split the request up into
multiple bios if appropriate. Neither does the function wait for
completion -- it's expected that callers won't care about when, or even
_if_, the request completes. It's only a hint to the device anyway. By
definition, the file system doesn't _care_ about these sectors any more.
[With feedback from OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> and
Jens Axboe <jens.axboe@oracle.com]
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 580b513..eb01313 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -86,7 +86,8 @@
#define READ_META (READ | (1 << BIO_RW_META))
#define WRITE_SYNC (WRITE | (1 << BIO_RW_SYNC))
#define SWRITE_SYNC (SWRITE | (1 << BIO_RW_SYNC))
-#define WRITE_BARRIER ((1 << BIO_RW) | (1 << BIO_RW_BARRIER))
+#define WRITE_BARRIER (WRITE | (1 << BIO_RW_BARRIER))
+#define WRITE_DISCARD (WRITE | (1 << BIO_RW_DISCARD))
#define SEL_IN 1
#define SEL_OUT 2