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

To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] fs: Add new pre-allocation ioctls to vfs for compatibility with legacy xfs ioctls
From: Arnd Bergmann <arnd@xxxxxxxx>
Date: Sat, 31 Jan 2009 01:38:32 +0100
Cc: Ankit Jain <me@xxxxxxxxxxxxx>, viro@xxxxxxxxxxxxxxxxxx, hch@xxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, mfasheh@xxxxxxxx, joel.becker@xxxxxxxxxx, ocfs2-devel@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs-masters@xxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20090130162252.7bf9c1f4.akpm@xxxxxxxxxxxxxxxxxxxx>
References: <4980C71F.1010804@xxxxxxxxxxxxx> <20090130162252.7bf9c1f4.akpm@xxxxxxxxxxxxxxxxxxxx>
User-agent: KMail/1.9.9
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 <><

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