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authorJens Axboe <jens.axboe@oracle.com>2008-10-09 03:01:10 -0400
committerJens Axboe <jens.axboe@oracle.com>2008-10-09 03:01:10 -0400
commitaf5639424008ffe96f89b059bea1aec15e0115a9 (patch)
tree5055712fa33e4878c97ff240d7755c6413627baf /include/linux
parent6feef531f55cf4a20fd9eb39f5352e5745203603 (diff)
block: add some comments around the bio read-write flags
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/bio.h12
1 files changed, 11 insertions, 1 deletions
diff --git a/include/linux/bio.h b/include/linux/bio.h
index fb97221d7c30..ff5b4cf9e2da 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -123,13 +123,23 @@ struct bio {
123/* 123/*
124 * bio bi_rw flags 124 * bio bi_rw flags
125 * 125 *
126 * bit 0 -- read (not set) or write (set) 126 * bit 0 -- data direction
127 * If not set, bio is a read from device. If set, it's a write to device.
127 * bit 1 -- rw-ahead when set 128 * bit 1 -- rw-ahead when set
128 * bit 2 -- barrier 129 * bit 2 -- barrier
130 * Insert a serialization point in the IO queue, forcing previously
131 * submitted IO to be completed before this oen is issued.
129 * bit 3 -- fail fast, don't want low level driver retries 132 * bit 3 -- fail fast, don't want low level driver retries
130 * bit 4 -- synchronous I/O hint: the block layer will unplug immediately 133 * bit 4 -- synchronous I/O hint: the block layer will unplug immediately
134 * Note that this does NOT indicate that the IO itself is sync, just
135 * that the block layer will not postpone issue of this IO by plugging.
131 * bit 5 -- metadata request 136 * bit 5 -- metadata request
137 * Used for tracing to differentiate metadata and data IO. May also
138 * get some preferential treatment in the IO scheduler
132 * bit 6 -- discard sectors 139 * bit 6 -- discard sectors
140 * Informs the lower level device that this range of sectors is no longer
141 * used by the file system and may thus be freed by the device. Used
142 * for flash based storage.
133 */ 143 */
134#define BIO_RW 0 /* Must match RW in req flags (blkdev.h) */ 144#define BIO_RW 0 /* Must match RW in req flags (blkdev.h) */
135#define BIO_RW_AHEAD 1 /* Must match FAILFAST in req flags */ 145#define BIO_RW_AHEAD 1 /* Must match FAILFAST in req flags */