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SubjectRe: [Patch v2] block: introduce block_rq_error tracepoint
On Mon, 20 Jan 2020 14:26:18 -0800
Cong Wang <xiyou.wangcong@gmail.com> wrote:

> ---
> 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..37e99be19536 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 )
> + __dynamic_array( char, name, DISK_NAME_LEN )

Hmm, looks like I need to go and do a clean up of the kernel, and
educate people on how to use dynamic arrays :-/

The "len" field of a __dynamic_array() is to be a function to determine
the length needed for each instance of an event. By having a constant
there, it will be the same for every events, plus the meta data to hold
the "dynamic" part of the array. This would be much better to simple
use __array() instead.

But as you use "__assign_str()" below, then it's expected that name is
a nul terminated string. In which case, you want to define this as:

__string( name, rq->rq_disk ? rq->rq_disk->disk_name : "?" )


> + __field( sector_t, sector )
> + __field( unsigned int, nr_sector )
> + __field( int, error )
> + __array( char, rwbs, RWBS_LEN )
> + __dynamic_array( char, cmd, 1 )

Not sure what you are doing with cmd. It appears to be always hard
coded as an empty string?

-- Steve


> + ),
> +
> + TP_fast_assign(
> + __entry->dev = rq->rq_disk ? disk_devt(rq->rq_disk) : 0;
> + __assign_str(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),
> + __get_str(name), __entry->rwbs, __get_str(cmd),
> + (unsigned long long)__entry->sector,
> + __entry->nr_sector, __entry->error)
> +);
> +
> DECLARE_EVENT_CLASS(block_rq,
>
> TP_PROTO(struct request_queue *q, struct request *rq),

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