On Wed, 06 Mar 2013 20:47:51 +0000 David Howells <dhowells@xxxxxxxxxx> wrote:
> In the UAPI header files, __BIG_ENDIAN and __LITTLE_ENDIAN must be compared
> against __BYTE_ORDER in preprocessor conditionals where these are exposed to
> userspace (that is they're not inside __KERNEL__ conditionals).
>
> However, in the main kernel the norm is to check for "defined(__XXX_ENDIAN)"
> rather than comparing against __BYTE_ORDER and this has incorrectly leaked
> into the userspace headers.
>
> The definition of struct mdp_superblock_s in linux/raid/md_p.h is wrong in this
> way. Note that userspace will likely interpret the ordering of the fields
> incorrectly as the big-endian variant on a little-endian machines - depending
> on header inclusion order.
>
> [!!!] NOTE [!!!] This patch may adversely change the userspace API. It might
> be better to fix the ordering of events_hi, events_lo, cp_events_hi and
> cp_events_lo in struct mdp_superblock_s / typedef mdp_super_t.
Thanks David - looks good to me.
Changing the ordering of fields isn't really an option at this stage - over
10 years too late :-(.
I think any user-space tools that use this data structure have their own copy
of the include file.
Acked-by: NeilBrown <neilb@xxxxxxx>
Thanks,
NeilBrown
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Neil Brown <neilb@xxxxxxx>
> cc: linux-raid@xxxxxxxxxxxxxxx
> ---
>
> include/uapi/linux/raid/md_p.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
> index ee75353..fe1a540 100644
> --- a/include/uapi/linux/raid/md_p.h
> +++ b/include/uapi/linux/raid/md_p.h
> @@ -145,16 +145,18 @@ typedef struct mdp_superblock_s {
> __u32 failed_disks; /* 4 Number of failed disks */
> __u32 spare_disks; /* 5 Number of spare disks */
> __u32 sb_csum; /* 6 checksum of the whole superblock */
> -#ifdef __BIG_ENDIAN
> +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> __u32 events_hi; /* 7 high-order of superblock update count */
> __u32 events_lo; /* 8 low-order of superblock update count */
> __u32 cp_events_hi; /* 9 high-order of checkpoint update count */
> __u32 cp_events_lo; /* 10 low-order of checkpoint update count */
> -#else
> +#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> __u32 events_lo; /* 7 low-order of superblock update count */
> __u32 events_hi; /* 8 high-order of superblock update count */
> __u32 cp_events_lo; /* 9 low-order of checkpoint update count */
> __u32 cp_events_hi; /* 10 high-order of checkpoint update count */
> +#else
> +#error unspecified endianness
> #endif
> __u32 recovery_cp; /* 11 recovery checkpoint sector count */
> /* There are only valid for minor_version > 90 */
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