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

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Date:	Sat, 20 Jun 2009 08:13:59 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Ankit Jain <me@...itjain.org>, Al Viro <viro@...iv.linux.org.uk>,
	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 Friday 19 June 2009 06:28:07 pm Christoph Hellwig wrote:

> +/* on ia32 l_start is on a 32-bit boundary */
> +#if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
> +struct space_resv_32 {
> +	__s16		l_type;
> +	__s16		l_whence;
> +	__s64		l_start	__attribute__((packed));
> +			/* len == 0 means until end of file */
> +	__s64		l_len __attribute__((packed));
> +	__s32		l_sysid;
> +	__u32		l_pid;
> +	__s32		l_pad[4];	/* reserve area */
> +};
> +
> +#define FS_IOC_RESVSP_32		_IOW ('X', 40, struct space_resv_32)
> +#define FS_IOC_RESVSP64_32	_IOW ('X', 42, struct space_resv_32)

I'd just define this using compat_s64 instead of __s64 __packed so we can
use the same code on all architectures, even at the small cost of extra
text size on non-x86 architectures.

> +/* just account for different alignment */
> +static int compat_ioctl_preallocate(struct file *file, unsigned long arg)
> +{
> +	struct space_resv_32	__user *p32 = (void __user *)arg;
> +	struct space_resv	__user *p = compat_alloc_user_space(sizeof(*p));
> +
> +	if (copy_in_user(&p->l_type,	&p32->l_type,	sizeof(s16)) ||
> +	    copy_in_user(&p->l_whence,	&p32->l_whence, sizeof(s16)) ||
> +	    copy_in_user(&p->l_start,	&p32->l_start,	sizeof(s64)) ||
> +	    copy_in_user(&p->l_len,	&p32->l_len,	sizeof(s64)) ||
> +	    copy_in_user(&p->l_sysid,	&p32->l_sysid,	sizeof(s32)) ||
> +	    copy_in_user(&p->l_pid,	&p32->l_pid,	sizeof(u32)) ||
> +	    copy_in_user(&p->l_pad,	&p32->l_pad,	4*sizeof(u32)))
> +		return -EFAULT;
> +
> +	return ioctl_preallocate(file, p);
> +}
> +#endif
> +

Here, you can call do_fallocate directly in the same way that ioctl_preallocate
does, replacing the copy_in_user calls with __get_user().

	Arnd <><
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