Complements v2.6.31 commit 55782138e47d ("tracing/events: convert block
trace points to TRACE_EVENT()") to be equivalent to traditional blktrace
output. Also this allows event filtering to not always get all (un)plug
events.
NB: The NULL pointer check for q->kobj.parent is certainly racy and
I don't have enough experience if it's good enough for a trace event.
The change did work for my cases (block device read/write I/O on
zfcp-attached SCSI disks and dm-mpath on top).
While I haven't seen any prior art using driver core (parent) relations
for trace events, there are other cases using this when no direct pointer
exists between objects, such as:
#define to_scsi_target(d) container_of(d, struct scsi_target, dev)
static inline struct scsi_target *scsi_target(struct scsi_device *sdev)
{
return to_scsi_target(sdev->sdev_gendev.parent);
}
This is the object model we make use of here:
struct gendisk {
struct hd_struct {
struct device { /*container_of*/
struct kobject kobj; <--+
dev_t devt; /*deref*/ |
} __dev; |
} part0; |
struct request_queue *queue; ..+ |
} : |
: |
struct request_queue { <..............+ |
/* queue kobject */ |
struct kobject { |
struct kobject *parent; --------+
} kobj;
}
The parent pointer comes from:
#define disk_to_dev(disk) (&(disk)->part0.__dev)
int blk_register_queue(struct gendisk *disk)
struct device *dev = disk_to_dev(disk);
struct request_queue *q = disk->queue;
ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue");
^^^parent
$ ls -d /sys/block/sdf/queue
/sys/block/sda/queue
$ cat /sys/block/sdf/dev
80:0
A partition does not have its own request queue:
$ cat /sys/block/sdf/sdf1/dev
8:81
$ ls -d /sys/block/sdf/sdf1/queue
ls: cannot access '/sys/block/sdf/sdf1/queue': No such file or directory
The difference to blktrace parsed output is that block events don't use the
partition's minor number but the containing block device's minor number:
$ dd if=/dev/sdf1 count=1
$ cat /sys/kernel/debug/tracing/trace
block_bio_remap: 8,80 R 2048 + 32 <- (8,81) 0
block_bio_queue: 8,80 R 2048 + 32 [dd]
block_getrq: 8,80 R 2048 + 32 [dd]
block_plug: 8,80 [dd]
^^^^
block_rq_insert: 8,80 R 16384 () 2048 + 32 [dd]
block_unplug: 8,80 [dd] 1 explicit
^^^^
block_rq_issue: 8,80 R 16384 () 2048 + 32 [dd]
block_rq_complete: 8,80 R () 2048 + 32 [0]
$ btrace /dev/sdf1
8,80 1 1 0.000000000 240240 A R 2048 + 32 <- (8,81) 0
8,81 1 2 0.000220890 240240 Q R 2048 + 32 [dd]
8,81 1 3 0.000229639 240240 G R 2048 + 32 [dd]
8,81 1 4 0.000231805 240240 P N [dd]
^^
8,81 1 5 0.000234671 240240 I R 2048 + 32 [dd]
8,81 1 6 0.000236365 240240 U N [dd] 1
^^
8,81 1 7 0.000238527 240240 D R 2048 + 32 [dd]
8,81 2 2 0.000613741 0 C R 2048 + 32 [0]
Signed-off-by: Steffen Maier <maier@xxxxxxxxxxxxx>
---
include/trace/events/block.h | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index e90bb6eb8097..6ea5a3899c2e 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -460,14 +460,18 @@ TRACE_EVENT(block_plug,
TP_ARGS(q),
TP_STRUCT__entry(
+ __field( dev_t, dev )
__array( char, comm, TASK_COMM_LEN )
),
TP_fast_assign(
+ __entry->dev = q->kobj.parent ?
+ container_of(q->kobj.parent, struct device, kobj)->devt : 0;
memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
),
- TP_printk("[%s]", __entry->comm)
+ TP_printk("%d,%d [%s]",
+ MAJOR(__entry->dev), MINOR(__entry->dev), __entry->comm)
);
#define show_block_unplug_explicit(val) \
@@ -482,18 +486,23 @@ DECLARE_EVENT_CLASS(block_unplug,
TP_ARGS(q, depth, explicit),
TP_STRUCT__entry(
+ __field( dev_t, dev )
__field( int, nr_rq )
__field( bool, explicit )
__array( char, comm, TASK_COMM_LEN )
),
TP_fast_assign(
+ __entry->dev = q->kobj.parent ?
+ container_of(q->kobj.parent, struct device, kobj)->devt : 0;
__entry->nr_rq = depth;
__entry->explicit = explicit;
memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
),
- TP_printk("[%s] %d %s", __entry->comm, __entry->nr_rq,
+ TP_printk("%d,%d [%s] %d %s",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ __entry->comm, __entry->nr_rq,
show_block_unplug_explicit(__entry->explicit))
);
--
2.13.5
