Re: [PATCH] ceph: avoid call to strlen() in ceph_mds_auth_match()

[Luis Henriques <luis.henriques@linux.dev>]

On Tue 18 Jun 2024 05:36:40 PM +03, Dmitry Antipov wrote;

> Since 'snprintf()' returns the number of characters emitted,
> an extra call to 'strlen()' in 'ceph_mds_auth_match()' may
> be dropped. Compile tested only.
>
> Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
> ---
>  fs/ceph/mds_client.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index c2157f6e0c69..7224283046a7 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -5665,9 +5665,9 @@ static int ceph_mds_auth_match(struct ceph_mds_client *mdsc,
>  				if (!_tpath)
>  					return -ENOMEM;
>  				/* remove the leading '/' */
> -				snprintf(_tpath, n, "%s/%s", spath + 1, tpath);
> +				tlen = snprintf(_tpath, n, "%s/%s",
> +						spath + 1, tpath);
>  				free_tpath = true;
> -				tlen = strlen(_tpath);
>  			}

Unless I'm missing something, this patch is incorrect.  snprintf() may not
return the actual string length *if* the output is truncated.  For
example:

	snprintf(str, 5, "%s", "0123456789");

snprintf() will return 10, while strlen(str) will return 4.

Cheers,
-- 
Luís