8 is not the maximum size of the suffix used when creating debugfs files.

Let the compiler compute the correct size, and only give a hint about the
longest possible string that is used.

When building with W=1, this fixes the following warnings:

  fs/dlm/debug_fs.c: In function ‘dlm_create_debug_file’:
  fs/dlm/debug_fs.c:1020:58: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
   1020 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_waiters", ls->ls_name);
        |                                                          ^
  fs/dlm/debug_fs.c:1020:9: note: ‘snprintf’ output between 9 and 73 bytes into a destination of size 72
   1020 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_waiters", ls->ls_name);
        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  fs/dlm/debug_fs.c:1031:50: error: ‘_queued_asts’ directive output may be truncated writing 12 bytes into a region of size between 8 and 72 [-Werror=format-truncation=]
   1031 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_queued_asts", ls->ls_name);
        |                                                  ^~~~~~~~~~~~
  fs/dlm/debug_fs.c:1031:9: note: ‘snprintf’ output between 13 and 77 bytes into a destination of size 72
   1031 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_queued_asts", ls->ls_name);
        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 541adb0d4d10b ("fs: dlm: debugfs for queued callbacks")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
 fs/dlm/debug_fs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/dlm/debug_fs.c b/fs/dlm/debug_fs.c
index e9726c6cbdf2..c93359ceaae6 100644
--- a/fs/dlm/debug_fs.c
+++ b/fs/dlm/debug_fs.c
@@ -973,7 +973,8 @@ void dlm_delete_debug_comms_file(void *ctx)
 
 void dlm_create_debug_file(struct dlm_ls *ls)
 {
-	char name[DLM_LOCKSPACE_LEN + 8];
+	/* Reserve enough space for the longest file name */
+	char name[DLM_LOCKSPACE_LEN + sizeof("_queued_asts")];
 
 	/* format 1 */
 
-- 
2.34.1

Hi,

On Fri, Sep 22, 2023 at 1:38 PM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> 8 is not the maximum size of the suffix used when creating debugfs files.
>
> Let the compiler compute the correct size, and only give a hint about the
> longest possible string that is used.
>
> When building with W=1, this fixes the following warnings:
>
>   fs/dlm/debug_fs.c: In function ‘dlm_create_debug_file’:
>   fs/dlm/debug_fs.c:1020:58: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
>    1020 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_waiters", ls->ls_name);
>         |                                                          ^
>   fs/dlm/debug_fs.c:1020:9: note: ‘snprintf’ output between 9 and 73 bytes into a destination of size 72
>    1020 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_waiters", ls->ls_name);
>         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   fs/dlm/debug_fs.c:1031:50: error: ‘_queued_asts’ directive output may be truncated writing 12 bytes into a region of size between 8 and 72 [-Werror=format-truncation=]
>    1031 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_queued_asts", ls->ls_name);
>         |                                                  ^~~~~~~~~~~~
>   fs/dlm/debug_fs.c:1031:9: note: ‘snprintf’ output between 13 and 77 bytes into a destination of size 72
>    1031 |         snprintf(name, DLM_LOCKSPACE_LEN + 8, "%s_queued_asts", ls->ls_name);
>         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Fixes: 541adb0d4d10b ("fs: dlm: debugfs for queued callbacks")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

there is a similar patch [0] already in the queue for dlm.

- Alex

[0] https://lore.kernel.org/gfs2/20230906143153.1353077-5-aahringo@redhat.com/T/#u