[Devel] [PATCH RH8] ploop: Provide more info about ENOSPC

[Cyrill Gorcunov]

On Wed, Oct 20, 2021 at 06:13:01PM +0300, Kirill Tkhai wrote:
...
> diff --git a/drivers/md/dm-ploop-target.c b/drivers/md/dm-ploop-target.c
> index 327095f75359..bd68d5fb272b 100644
> --- a/drivers/md/dm-ploop-target.c
> +++ b/drivers/md/dm-ploop-target.c
> @@ -455,6 +455,8 @@ static void ploop_status(struct dm_target *ti, status_type_t type,
>  		p += sprintf(p, "t");
>  	if (READ_ONCE(ploop->noresume))
>  		p += sprintf(p, "n");
> +	if (READ_ONCE(ploop->event_enospc))
> +		p += sprintf(p, "s");
>  	if (p == stat)
>  		p += sprintf(p, "o");
>  	if (ploop->skip_off)

While I've no clue what is going on here with this status I wonder why
we use sprintf here at all? The sprintf is _very_ heavy function which
consumes too much cycles for nothing, we don't even need any formatting
here. Why not some simple

static void ploop_status(struct dm_target *ti, status_type_t type,
			 unsigned int status_flags, char *result,
			 unsigned int maxlen)
{
	struct ploop *ploop = ti->private;
	char stat[16], *p = stat;
	ssize_t sz = 0;

	down_read(&ploop->ctl_rwsem);
	if (ploop->falloc_new_clu)
		*p++ = 'f';
	if (ploop->tracking_bitmap)
		*p++ = 't';
	if (READ_ONCE(ploop->noresume))
		*p++ = 'n';
	if (p == stat)
		*p++ = 'o';
	*p = '\0';
	up_read(&ploop->ctl_rwsem);

	BUG_ON(p - stat >= sizeof(stat));
	DMEMIT("%u v2 %u %s", ploop->nr_deltas, (u32)CLU_TO_SEC(ploop, 1), stat);
}

or I miss something obvious?