blktrace: support per-partition tracing

Though one can specify '-d /dev/sda1' when using blktrace, it still
traces the whole sda.

To support per-partition tracing, when we start tracing, we initialize
bt->start_lba and bt->end_lba to the start and end sector of that
partition.

Note some actions are per device, thus we don't filter 0-sector events.

The original patch and discussion can be found here:
	http://marc.info/?l=linux-btrace&m=122949374214540&w=2

Signed-off-by: Shawn Du <duyuyang@gmail.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
LKML-Reference: <49E42620.4050701@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 82312df9b0bf..49c98730bb8d 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1065,6 +1065,7 @@ sg_ioctl(struct inode *inode, struct file *filp,
                 return blk_trace_setup(sdp->device->request_queue,
                                        sdp->disk->disk_name,
                                        MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
+                                       NULL,
                                        (char *)arg);
         case BLKTRACESTART:
                 return blk_trace_startstop(sdp->device->request_queue, 1);