linux-kernel - Re: [PATCH v2] afs: use correct format characters

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Date:   Wed, 10 Apr 2019 15:52:25 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Louis Taylor <louis@...gniz.eu>
Cc:     David Howells <dhowells@...hat.com>, linux-afs@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v2] afs: use correct format characters

On Wed, Apr 10, 2019 at 3:41 PM Louis Taylor <louis@...gniz.eu> wrote:
>
> When compiling with -Wformat, clang warns:
>
> fs/afs/flock.c:632:29: warning: format specifies type 'short' but the argument has type
>       'unsigned char' [-Wformat]
>         _leave(" = %d [%hd]", ret, fl->fl_type);
>                        ~~~         ^~~~~~~~~~~
>
> fs/afs/dir.c:138:11: warning: format specifies type 'unsigned short' but
> the argument has type 'int' [-Wformat]
>        ntohs(dbuf->blocks[tmp].hdr.magic));
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> fl_type is declared as an unsigned char unconditionally in
> include/linux/fs.h, so use the correct format characters.

Thanks for the v2, probably should include a note about ntohs.  That
case in particular looks more complicated, due to the definition of
ntohs (which uses __swab16).

If you keep the previous flag of %04hx, but add an explicit cast to
u16, does the warning go away? If so, that might be a better fix.

- ntohs(dbuf->blocks[tmp].hdr.magic));
+ (u16)ntohs(dbuf->blocks[tmp].hdr.magic));

?

Particularly, I'm curious about the return type of GNU C statement
expressions, in the definition of __swab16 if __HAVE_BUILTIN_BSWAP16__
is not defined.

>
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Signed-off-by: Louis Taylor <louis@...gniz.eu>
> ---
>  fs/afs/dir.c   | 2 +-
>  fs/afs/flock.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/afs/dir.c b/fs/afs/dir.c
> index 8a2562e3a316..4ceaec94e9c5 100644
> --- a/fs/afs/dir.c
> +++ b/fs/afs/dir.c
> @@ -133,7 +133,7 @@ static bool afs_dir_check_page(struct afs_vnode *dvnode, struct page *page,
>         dbuf = kmap(page);
>         for (tmp = 0; tmp < qty; tmp++) {
>                 if (dbuf->blocks[tmp].hdr.magic != AFS_DIR_MAGIC) {
> -                       printk("kAFS: %s(%lx): bad magic %d/%d is %04hx\n",
> +                       printk("kAFS: %s(%lx): bad magic %d/%d is %04x\n",
>                                __func__, dvnode->vfs_inode.i_ino, tmp, qty,
>                                ntohs(dbuf->blocks[tmp].hdr.magic));
>                         trace_afs_dir_check_failed(dvnode, off, i_size);
> diff --git a/fs/afs/flock.c b/fs/afs/flock.c
> index 6a0174258382..be4c3f6a3178 100644
> --- a/fs/afs/flock.c
> +++ b/fs/afs/flock.c
> @@ -629,7 +629,7 @@ static int afs_do_getlk(struct file *file, struct file_lock *fl)
>
>         ret = 0;
>  error:
> -       _leave(" = %d [%hd]", ret, fl->fl_type);
> +       _leave(" = %d [%hhu]", ret, fl->fl_type);
>         return ret;
>  }

-
Thanks,
~Nick Desaulniers