Re: [PATCH] xfs: Fix format specifier for max_folio_size in xfs_fs_fill_super()

[Matthew Wilcox <willy@infradead.org>]

On Tue, Aug 27, 2024 at 04:15:05PM -0700, Nathan Chancellor wrote:
> When building for a 32-bit architecture, where 'size_t' is 'unsigned
> int', there is a warning due to use of '%ld', the specifier for a 'long
> int':
> 
>   In file included from fs/xfs/xfs_linux.h:82,
>                    from fs/xfs/xfs.h:26,
>                    from fs/xfs/xfs_super.c:7:
>   fs/xfs/xfs_super.c: In function 'xfs_fs_fill_super':
>   fs/xfs/xfs_super.c:1654:1: error: format '%ld' expects argument of type 'long int', but argument 5 has type 'size_t' {aka 'unsigned int'} [-Werror=format=]
>    1654 | "block size (%u bytes) not supported; Only block size (%ld) or less is supported",
>         | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    1655 |                                 mp->m_sb.sb_blocksize, max_folio_size);
>         |                                                        ~~~~~~~~~~~~~~
>         |                                                        |
>         |                                                        size_t {aka unsigned int}
>   ...
>   fs/xfs/xfs_super.c:1654:58: note: format string is defined here
>    1654 | "block size (%u bytes) not supported; Only block size (%ld) or less is supported",
>         |                                                        ~~^
>         |                                                          |
>         |                                                          long int
>         |                                                        %d

Do we really need the incredibly verbose compiler warning messages?
Can't we just say "this is the wrong format specifier on 32 bit"
and be done with it?

> Use the proper 'size_t' specifier, '%zu', to resolve the warning.
> 
> Fixes: 0ab3ca31b012 ("xfs: enable block size larger than page size support")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  fs/xfs/xfs_super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 242271298a33..e8cc7900911e 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1651,7 +1651,7 @@ xfs_fs_fill_super(
>  
>  		if (mp->m_sb.sb_blocksize > max_folio_size) {
>  			xfs_warn(mp,
> -"block size (%u bytes) not supported; Only block size (%ld) or less is supported",
> +"block size (%u bytes) not supported; Only block size (%zu) or less is supported",
>  				mp->m_sb.sb_blocksize, max_folio_size);
>  			error = -ENOSYS;
>  			goto out_free_sb;
> 
> ---
> base-commit: f143d1a48d6ecce12f5bced0d18a10a0294726b5
> change-id: 20240827-xfs-fix-wformat-bs-gt-ps-967f3aa1c142
> 
> Best regards,
> -- 
> Nathan Chancellor <nathan@kernel.org>
> 
>