On Wed, 06 Mar 2013 20:47:51 +0000 David Howells <[email protected]> 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 <[email protected]> Thanks, NeilBrown > > Signed-off-by: David Howells <[email protected]> > cc: Neil Brown <[email protected]> > cc: [email protected] > --- > > 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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