On Fri, 10 Jan 2020 14:15:00 -0800
Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> Currently, rasdaemon uses the existing tracepoint block_rq_complete
> and filters out non-error cases in order to capture block disk errors.
>
> But there are a few problems with this approach:
>
> 1. Even kernel trace filter could do the filtering work, there is
> still some overhead after we enable this tracepoint.
>
> 2. The filter is merely based on errno, which does not align with kernel
> logic to check the errors for print_req_error().
>
> 3. block_rq_complete only provides dev major and minor to identify
> the block device, it is not convenient to use in user-space.
>
> So introduce a new tracepoint block_rq_error just for the error case
> and provides the device name for convenience too. With this patch,
> rasdaemon could switch to block_rq_error.
>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> ---
> block/blk-core.c | 4 +++-
> include/trace/events/block.h | 43 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 089e890ab208..0c7ad70d06be 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1450,8 +1450,10 @@ bool blk_update_request(struct request *req, blk_status_t error,
> #endif
>
> if (unlikely(error && !blk_rq_is_passthrough(req) &&
> - !(req->rq_flags & RQF_QUIET)))
> + !(req->rq_flags & RQF_QUIET))) {
> + trace_block_rq_error(req, blk_status_to_errno(error), nr_bytes);
> print_req_error(req, error, __func__);
> + }
>
> blk_account_io_completion(req, nr_bytes);
>
> diff --git a/include/trace/events/block.h b/include/trace/events/block.h
> index 81b43f5bdf23..a0f63f4d50c4 100644
> --- a/include/trace/events/block.h
> +++ b/include/trace/events/block.h
> @@ -145,6 +145,49 @@ TRACE_EVENT(block_rq_complete,
> __entry->nr_sector, __entry->error)
> );
>
> +/**
> + * block_rq_error - block IO operation error reported by device driver
> + * @rq: block operations request
> + * @error: status code
> + * @nr_bytes: number of completed bytes
> + *
> + * The block_rq_error tracepoint event indicates that some portion
> + * of operation request has failed as reported by the device driver.
> + */
> +TRACE_EVENT(block_rq_error,
> +
> + TP_PROTO(struct request *rq, int error, unsigned int nr_bytes),
> +
> + TP_ARGS(rq, error, nr_bytes),
> +
> + TP_STRUCT__entry(
> + __field( dev_t, dev )
> + __field( char *, name )
Please make this a string() field and not a pointer to name.
> + __field( sector_t, sector )
> + __field( unsigned int, nr_sector )
> + __field( int, error )
> + __array( char, rwbs, RWBS_LEN )
> + __dynamic_array( char, cmd, 1 )
> + ),
> +
> + TP_fast_assign(
> + __entry->dev = rq->rq_disk ? disk_devt(rq->rq_disk) : 0;
> + __entry->name = rq->rq_disk ? rq->rq_disk->disk_name : "?";
> + __entry->sector = blk_rq_pos(rq);
> + __entry->nr_sector = nr_bytes >> 9;
> + __entry->error = error;
> +
> + blk_fill_rwbs(__entry->rwbs, rq->cmd_flags, nr_bytes);
> + __get_str(cmd)[0] = '\0';
> + ),
> +
> + TP_printk("%d,%d %s %s (%s) %llu + %u [%d]",
> + MAJOR(__entry->dev), MINOR(__entry->dev),
> + __entry->name, __entry->rwbs, __get_str(cmd),
The ring buffer will hold a pointer to a location that may no longer
exist, and cause a fault when read. Also, this makes the user space
utilities trace-cmd and perf useless to know what the name is, as they
read the raw ring buffer data directly.
-- Steve
> + (unsigned long long)__entry->sector,
> + __entry->nr_sector, __entry->error)
> +);
> +
> DECLARE_EVENT_CLASS(block_rq,
>
> TP_PROTO(struct request_queue *q, struct request *rq),
