Re: [PATCH v2 10/15] blktrace: differentiate between blk_io_trace versions

Damien Le Moal
2025-10-01T07:21:42Z

On 9/26/25 00:02, Johannes Thumshirn wrote:
> Differentiate between blk_io_trace and blk_io_trace2 when relaying to
> user-space depending on which version has been requested by the blktrace
> utility.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
> kernel/trace/blktrace.c | 62 +++++++++++++++++++++++++++++++++++++----
> 1 file changed, 57 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 9cd8eb9e7b4b..82ad626d6202 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -91,6 +91,29 @@ static void record_blktrace_event(struct blk_io_trace *t, pid_t pid, int cpu,
> memcpy((void *)t + sizeof(*t) + cgid_len, pdu_data, pdu_len);
> }
>
> +static void record_blktrace_event2(struct blk_io_trace2 *t2, pid_t pid, int cpu,
> + sector_t sector, int bytes, u64 what,
> + dev_t dev, int error, u64 cgid,
> + ssize_t cgid_len, void *pdu_data,
> + int pdu_len)
> +

Extra blank line not needed.

> +{
> + t2->pid = pid;
> + t2->cpu = cpu;
> +
> + t2->sector = sector;
> + t2->bytes = bytes;
> + t2->action = what;
> + t2->device = dev;
> + t2->error = error;
> + t2->pdu_len = pdu_len + cgid_len;
> +
> + if (cgid_len)
> + memcpy((void *)t2 + sizeof(*t2), &cgid, cgid_len);
> + if (pdu_len)
> + memcpy((void *)t2 + sizeof(*t2) + cgid_len, pdu_data, pdu_len);
> +}
> +
> static void relay_blktrace_event(struct blk_trace *bt, unsigned long sequence,
> pid_t pid, int cpu, sector_t sector, int bytes,
> u32 what, int error, u64 cgid,
> @@ -111,6 +134,26 @@ static void relay_blktrace_event(struct blk_trace *bt, unsigned long sequence,
> cgid, cgid_len, pdu_data, pdu_len);
> }
>
> +static void relay_blktrace_event2(struct blk_trace *bt, unsigned long sequence,
> + pid_t pid, int cpu, sector_t sector,
> + int bytes, u64 what, int error, u64 cgid,
> + ssize_t cgid_len, void *pdu_data, int pdu_len)
> +{
> + struct blk_io_trace2 *t;
> + size_t trace_len = sizeof(struct blk_io_trace2) + pdu_len + cgid_len;
> +
> + t = relay_reserve(bt->rchan, trace_len);
> + if (!t)
> + return;
> +
> + t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE2_VERSION;
> + t->sequence = sequence;
> + t->time = ktime_to_ns(ktime_get());
> +
> + record_blktrace_event2(t, pid, cpu, sector, bytes, what, bt->dev, error,
> + cgid, cgid_len, pdu_data, pdu_len);
> +}

See below.

> +
> /*
> * Send out a notify message.
> */
> @@ -146,8 +189,12 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
> if (!bt->rchan)
> return;
>
> - relay_blktrace_event(bt, 0, pid, cpu, 0, 0, action, 0, cgid,
> - cgid_len, (void *)data, len);
> + if (bt->version == 1)
> + relay_blktrace_event(bt, 0, pid, cpu, 0, 0, action, 0, cgid,
> + cgid_len, (void *)data, len);
> + else
> + relay_blktrace_event2(bt, 0, pid, cpu, 0, 0, action, 0, cgid,
> + cgid_len, (void *)data, len);

Since you pass bt pointer to the relay function, the version is known in that
function and this could be done inside it, no ?
That would avoid this if repetition.

> }
>
> /*
> @@ -329,9 +376,14 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
> local_irq_save(flags);
> sequence = per_cpu_ptr(bt->sequence, cpu);
> (*sequence)++;
> - relay_blktrace_event(bt, *sequence, pid, cpu, sector, bytes,
> - lower_32_bits(what), error, cgid, cgid_len,
> - pdu_data, pdu_len);
> + if (bt->version == 1)
> + relay_blktrace_event(bt, *sequence, pid, cpu, sector, bytes,
> + lower_32_bits(what), error, cgid,
> + cgid_len, pdu_data, pdu_len);
> + else
> + relay_blktrace_event2(bt, *sequence, pid, cpu, sector, bytes,
> + what, error, cgid, cgid_len, pdu_data,
> + pdu_len);
> local_irq_restore(flags);
> }
>

--
Damien Le Moal
Western Digital Research