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

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Date:	Sat, 31 Jan 2009 01:38:32 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ankit Jain <me@...itjain.org>, viro@...iv.linux.org.uk,
	hch@...radead.org, linux-fsdevel@...r.kernel.org, mfasheh@...e.com,
	joel.becker@...cle.com, ocfs2-devel@....oracle.com,
	linux-kernel@...r.kernel.org, xfs-masters@....sgi.com,
	xfs@....sgi.com
Subject: Re: [PATCH] fs: Add new pre-allocation ioctls to vfs for compatibility with legacy xfs ioctls

On Saturday 31 January 2009, Andrew Morton wrote:
> On Thu, 29 Jan 2009 02:29:11 +0530 Ankit Jain <me@...itjain.org> 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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