Re: [PATCH v2] 9pfs: improve v9fs_walk() tracing

[Christian Schoenebeck]

On Friday, December 6, 2024 4:56:40 PM CET Christian Schoenebeck wrote:
> 'Twalk' is the most important request type in the 9p protocol to look out
> for when debugging 9p communication. That's because it is the only part
> of the 9p protocol which actually deals with human-readable path names,
> whereas all other 9p request types work on numeric file IDs (FIDs) only.
> 
> Improve tracing of 'Twalk' requests, e.g. let's say client wanted to walk
> to "/home/bob/src", then improve trace output from:
> 
>   v9fs_walk tag 0 id 110 fid 0 newfid 1 nwnames 3
> 
> to:
> 
>   v9fs_walk tag=0 id=110 fid=0 newfid=1 nwnames=3 wnames={home, bob, src}
> 
> To achieve this, add a new helper function trace_v9fs_walk_wnames() which
> converts the received V9fsString array of individual path elements into a
> comma-separated string presentation for being passed to the tracing system.
> As this conversion is somewhat expensive, this conversion function is only
> called if tracing of event 'v9fs_walk' is currently enabled.
> 
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> Reviewed-by: Greg Kurz <groug@kaod.org>
> ---
>  V2:
>  - Use trace_event_get_state_backends(TRACE_V9FS_WALK) instead of
>    trace_event_get_state(TRACE_V9FS_WALK) && qemu_loglevel_mask(LOG_TRACE).
>  - Move that check from helper function trace_v9fs_walk_wnames() to caller
>    function v9fs_walk().
> 
>  hw/9pfs/9p.c         | 36 +++++++++++++++++++++++++++++++-----
>  hw/9pfs/trace-events |  2 +-
>  2 files changed, 32 insertions(+), 6 deletions(-)

Queued on 9p.next:
https://github.com/cschoenebeck/qemu/commits/9p.next

Thanks!

/Christian