[Libguestfs] [PATCH nbdkit] nbd: Hide some state machine debugging behind a debug flag

[Laszlo Ersek]

On 05/10/22 11:43, Richard W.M. Jones wrote:
> When running virt-p2v which uses this plugin, the log file is consumed
> by messages about state machine transitions and so on.  In a log file
> that was shared with me, out of the 135,023 lines in total,
> 94,653 (70%) were:
> 
>   nbdkit: debug: polling, dir=1
> 
> and 18,676 (14%) were:
> 
>   nbdkit: debug: cookie X completed state machine, status 0
> 
> This commit changes the logging so these state machine transitions are
> only printed when you use the debug flag “-D nbd.verbose=1”.  I didn't
> document this flag because it's likely only of use to developers who
> are reading the code already.
> 
> There are some debug messages along error paths which are
> (a) generally useful and (b) did not appear in the log file, so I left
> those alone.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2083498
> Reported-by: Ming Xie
> ---
>  plugins/nbd/nbd.c | 24 +++++++++++++++++-------
>  1 file changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c
> index 45bf05e9..d0d6544b 100644
> --- a/plugins/nbd/nbd.c
> +++ b/plugins/nbd/nbd.c
> @@ -66,6 +66,9 @@
>  #define USE_VSOCK 1
>  #endif
>  
> +/* Use '-D nbd.verbose=1' for verbose messages about the state machine. */
> +NBDKIT_DLL_PUBLIC int nbd_debug_verbose = 0;
> +
>  /* The per-transaction details */
>  struct transaction {
>    int64_t cookie;
> @@ -421,7 +424,8 @@ nbdplug_reader (void *handle)
>  {
>    struct handle *h = handle;
>  
> -  nbdkit_debug ("nbd: started reader thread");
> +  if (nbd_debug_verbose)
> +    nbdkit_debug ("nbd: started reader thread");
>  
>    while (!nbd_aio_is_dead (h->nbd) && !nbd_aio_is_closed (h->nbd)) {
>      int r;
> @@ -433,7 +437,8 @@ nbdplug_reader (void *handle)
>      unsigned dir;
>  
>      dir = nbd_aio_get_direction (h->nbd);
> -    nbdkit_debug ("polling, dir=%d", dir);
> +    if (nbd_debug_verbose)
> +      nbdkit_debug ("polling, dir=%d", dir);
>      if (dir & LIBNBD_AIO_DIRECTION_READ)
>        fds[0].events |= POLLIN;
>      if (dir & LIBNBD_AIO_DIRECTION_WRITE)
> @@ -466,8 +471,11 @@ nbdplug_reader (void *handle)
>      }
>    }
>  
> -  nbdkit_debug ("state machine changed to %s", nbd_connection_state (h->nbd));
> -  nbdkit_debug ("exiting reader thread");
> +  if (nbd_debug_verbose) {
> +    nbdkit_debug ("state machine changed to %s",
> +                  nbd_connection_state (h->nbd));
> +    nbdkit_debug ("exiting reader thread");
> +  }
>    return NULL;
>  }
>  
> @@ -481,8 +489,9 @@ nbdplug_notify (void *opaque, int *error)
>     * updated by nbdplug_register, but it's only an informational
>     * message.
>     */
> -  nbdkit_debug ("cookie %" PRId64 " completed state machine, status %d",
> -                trans->cookie, *error);
> +  if (nbd_debug_verbose)
> +    nbdkit_debug ("cookie %" PRId64 " completed state machine, status %d",
> +                  trans->cookie, *error);
>    trans->err = *error;
>    if (sem_post (&trans->sem)) {
>      nbdkit_error ("failed to post semaphore: %m");
> @@ -514,7 +523,8 @@ nbdplug_register (struct handle *h, struct transaction *trans, int64_t cookie)
>      return;
>    }
>  
> -  nbdkit_debug ("cookie %" PRId64 " started by state machine", cookie);
> +  if (nbd_debug_verbose)
> +    nbdkit_debug ("cookie %" PRId64 " started by state machine", cookie);
>    trans->cookie = cookie;
>  
>    if (write (h->fds[1], &c, 1) == -1 && errno != EAGAIN)
> 

Reviewed-by: Laszlo Ersek <lersek at redhat.com>