Re: [PATCH 1/4] xfs: Use variable-size array for nameval in xfs_attr_sf_entry

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Aug 31, 2020 at 03:04:20PM +0200, Carlos Maiolino wrote:
> nameval is a variable-size array, so, define it as it, and remove all
> the -1 magic number subtractions.
> 
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_attr_leaf.c | 6 ++----
>  fs/xfs/libxfs/xfs_attr_sf.h   | 6 +++---
>  fs/xfs/libxfs/xfs_da_format.h | 2 +-
>  3 files changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index 305d4bc073370..7bbc97e0e4d4a 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -992,7 +992,7 @@ xfs_attr_shortform_allfit(
>  			return 0;
>  		if (be16_to_cpu(name_loc->valuelen) >= XFS_ATTR_SF_ENTSIZE_MAX)
>  			return 0;
> -		bytes += sizeof(struct xfs_attr_sf_entry) - 1
> +		bytes += sizeof(struct xfs_attr_sf_entry)
>  				+ name_loc->namelen
>  				+ be16_to_cpu(name_loc->valuelen);
>  	}
> @@ -1036,10 +1036,8 @@ xfs_attr_shortform_verify(
>  		 * struct xfs_attr_sf_entry has a variable length.
>  		 * Check the fixed-offset parts of the structure are
>  		 * within the data buffer.
> -		 * xfs_attr_sf_entry is defined with a 1-byte variable
> -		 * array at the end, so we must subtract that off.
>  		 */
> -		if (((char *)sfep + sizeof(*sfep) - 1) >= endp)
> +		if (((char *)sfep + sizeof(*sfep)) >= endp)
>  			return __this_address;
>  
>  		/* Don't allow names with known bad length. */
> diff --git a/fs/xfs/libxfs/xfs_attr_sf.h b/fs/xfs/libxfs/xfs_attr_sf.h
> index bb004fb7944a7..d93012a0be4d0 100644
> --- a/fs/xfs/libxfs/xfs_attr_sf.h
> +++ b/fs/xfs/libxfs/xfs_attr_sf.h
> @@ -28,11 +28,11 @@ typedef struct xfs_attr_sf_sort {
>  } xfs_attr_sf_sort_t;
>  
>  #define XFS_ATTR_SF_ENTSIZE_BYNAME(nlen,vlen)	/* space name/value uses */ \
> -	(((int)sizeof(xfs_attr_sf_entry_t)-1 + (nlen)+(vlen)))
> +	(((int)sizeof(xfs_attr_sf_entry_t) + (nlen)+(vlen)))
>  #define XFS_ATTR_SF_ENTSIZE_MAX			/* max space for name&value */ \
> -	((1 << (NBBY*(int)sizeof(uint8_t))) - 1)
> +	(1 << (NBBY*(int)sizeof(uint8_t)))

The maximum space for the name and value is still UINT8_MAX, right?
I don't think this should change to 256.

I also kind of wonder if this should also get changed to be more
direct:

#define XFS_ATTR_SF_ENTSIZE_MAX		(UINT8_MAX)

but it's working code, we could/should just leave it be...

>  #define XFS_ATTR_SF_ENTSIZE(sfep)		/* space an entry uses */ \
> -	((int)sizeof(xfs_attr_sf_entry_t)-1 + (sfep)->namelen+(sfep)->valuelen)
> +	((int)sizeof(xfs_attr_sf_entry_t) + (sfep)->namelen+(sfep)->valuelen)

Can this (and ENTSIZE_BYNAME) use struct_sizeof?

--D

>  #define XFS_ATTR_SF_NEXTENTRY(sfep)		/* next entry in struct */ \
>  	((xfs_attr_sf_entry_t *)((char *)(sfep) + XFS_ATTR_SF_ENTSIZE(sfep)))
>  #define XFS_ATTR_SF_TOTSIZE(dp)			/* total space in use */ \
> diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h
> index 059ac108b1b39..e86185a1165b3 100644
> --- a/fs/xfs/libxfs/xfs_da_format.h
> +++ b/fs/xfs/libxfs/xfs_da_format.h
> @@ -589,7 +589,7 @@ typedef struct xfs_attr_shortform {
>  		uint8_t namelen;	/* actual length of name (no NULL) */
>  		uint8_t valuelen;	/* actual length of value (no NULL) */
>  		uint8_t flags;	/* flags bits (see xfs_attr_leaf.h) */
> -		uint8_t nameval[1];	/* name & value bytes concatenated */
> +		uint8_t nameval[];	/* name & value bytes concatenated */
>  	} list[1];			/* variable sized array */
>  } xfs_attr_shortform_t;
>  
> -- 
> 2.26.2
>