Re: [PATCH] fs: Add new pre-allocation ioctls to vfs for compatibility with legacy xfs ioctls

[Arnd Bergmann <arnd@xxxxxxxx>]

On Saturday 31 January 2009, Andrew Morton wrote:
> On Thu, 29 Jan 2009 02:29:11 +0530 Ankit Jain <me@xxxxxxxxxxxxx> wrote:
> > +struct space_resv {
> > +   __s16           l_type;
> > +   __s16           l_whence;
> > +   __s64           l_start;
> > +   __s64           l_len;          /* len == 0 means until end of file */
> > +   __s32           l_sysid;
> > +   __u32           l_pid;
> > +   __s32           l_pad[4];       /* reserve area                     */
> > +};
> > +
> > +#define F_IOC_RESVSP               _IOW('X', 40, struct space_resv)
> > +#define F_IOC_RESVSP64             _IOW('X', 42, struct space_resv)
> 
> Are we sure that the aligment of l_start will be reliably the same
> across all compilers and versions thereof for all time?

On x86, the alignment differs between 32 and 64 bit, otherwise it's ok.
XFS handles the conversion for compat_ioctl in
fs/xfs/linux-2.6/xfs_ioctl32.c. If this becomes a generic file ioctl,
the conversion code should be moved to fs/compat_ioctl.c.

        Arnd <><