[PATCH] blktrace: readahead support

Provide the needed kernel support for distinguishing readahead
from regular read requests when tracing block devices.
Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Jens Axboe <axboe@suse.de>

block/blktrace.c

@@ -69,7 +69,7 @@ static u32 ddir_act[2] __read_mostly = { BLK_TC_ACT(BLK_TC_READ), BLK_TC_ACT(BLK
 /*
  * Bio action bits of interest
  */
-static u32 bio_act[3] __read_mostly = { 0, BLK_TC_ACT(BLK_TC_BARRIER), BLK_TC_ACT(BLK_TC_SYNC) };
+static u32 bio_act[5] __read_mostly = { 0, BLK_TC_ACT(BLK_TC_BARRIER), BLK_TC_ACT(BLK_TC_SYNC), 0, BLK_TC_ACT(BLK_TC_AHEAD) };
 
 /*
  * More could be added as needed, taking care to increment the decrementer
@@ -79,6 +79,8 @@ static u32 bio_act[3] __read_mostly = { 0, BLK_TC_ACT(BLK_TC_BARRIER), BLK_TC_AC
 	(((rw) & (1 << BIO_RW_BARRIER)) >> (BIO_RW_BARRIER - 0))
 #define trace_sync_bit(rw)	\
 	(((rw) & (1 << BIO_RW_SYNC)) >> (BIO_RW_SYNC - 1))
+#define trace_ahead_bit(rw)	\
+	(((rw) & (1 << BIO_RW_AHEAD)) << (BIO_RW_AHEAD - 0))
 
 /*
  * The worker for the various blk_add_trace*() types. Fills out a
@@ -100,6 +102,7 @@ void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	what |= ddir_act[rw & WRITE];
 	what |= bio_act[trace_barrier_bit(rw)];
 	what |= bio_act[trace_sync_bit(rw)];
+	what |= bio_act[trace_ahead_bit(rw)];
 
 	pid = tsk->pid;
 	if (unlikely(act_log_check(bt, what, sector, pid)))

include/linux/blktrace_api.h

@@ -19,6 +19,7 @@ enum blktrace_cat {
 	BLK_TC_FS	= 1 << 8,	/* fs requests */
 	BLK_TC_PC	= 1 << 9,	/* pc requests */
 	BLK_TC_NOTIFY	= 1 << 10,	/* special message */
+	BLK_TC_AHEAD	= 1 << 11,	/* readahead */
 
 	BLK_TC_END	= 1 << 15,	/* only 16-bits, reminder */
 };