linux-kernel - Re: [PATCH] xfs: Add __packed to xfs_dir2_sf_entry

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Message-ID: <20200115004353.GX8247@magnolia>
Date:   Tue, 14 Jan 2020 16:43:53 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     hch@....de, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: Add __packed to xfs_dir2_sf_entry_t definition

On Tue, Jan 14, 2020 at 12:03:52PM +0000, Vincenzo Frascino wrote:
> xfs_check_ondisk_structs() verifies that the sizes of the data types
> used by xfs are correct via the XFS_CHECK_STRUCT_SIZE() macro.
> 
> Since the structures padding can vary depending on the ABI (e.g. on
> ARM OABI structures are padded to multiple of 32 bits), it may happen
> that xfs_dir2_sf_entry_t size check breaks the compilation with the
> assertion below:
> 
> In file included from linux/include/linux/string.h:6,
>                  from linux/include/linux/uuid.h:12,
>                  from linux/fs/xfs/xfs_linux.h:10,
>                  from linux/fs/xfs/xfs.h:22,
>                  from linux/fs/xfs/xfs_super.c:7:
> In function ‘xfs_check_ondisk_structs’,
>     inlined from ‘init_xfs_fs’ at linux/fs/xfs/xfs_super.c:2025:2:
> linux/include/linux/compiler.h:350:38:
>     error: call to ‘__compiletime_assert_107’ declared with attribute
>     error: XFS: sizeof(xfs_dir2_sf_entry_t) is wrong, expected 3
>     _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> 
> Restore the correct behavior adding __packed to the structure definition.
> 
> Cc: Darrick J. Wong <darrick.wong@...cle.com>
> Suggested-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>

Will give this a spin,
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_da_format.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h
> index 3dee33043e09..60db25f30430 100644
> --- a/fs/xfs/libxfs/xfs_da_format.h
> +++ b/fs/xfs/libxfs/xfs_da_format.h
> @@ -217,7 +217,7 @@ typedef struct xfs_dir2_sf_entry {
>  	 * A 64-bit or 32-bit inode number follows here, at a variable offset
>  	 * after the name.
>  	 */
> -} xfs_dir2_sf_entry_t;
> +} __packed xfs_dir2_sf_entry_t;
>  
>  static inline int xfs_dir2_sf_hdr_size(int i8count)
>  {
> -- 
> 2.24.1
>