linux-kernel - Re: [PATCH 01/24] GFS2: Support for FIEMAP ioctl

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Message-Id: <20081217172255.44700cb6.akpm@linux-foundation.org>
Date:	Wed, 17 Dec 2008 17:22:55 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	swhiteho@...hat.com
Cc:	linux-kernel@...r.kernel.org, cluster-devel@...hat.com,
	swhiteho@...hat.com, tytso@....edu, sandeen@...hat.com
Subject: Re: [PATCH 01/24] GFS2: Support for FIEMAP ioctl

On Wed, 17 Dec 2008 11:30:00 +0000
swhiteho@...hat.com wrote:

> +static int gfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> +		       u64 start, u64 len)
> +{
> +	struct gfs2_inode *ip = GFS2_I(inode);
> +	struct gfs2_holder gh;
> +	int ret;
> +
> +	ret = fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC);
> +	if (ret)
> +		return ret;
> +
> +	mutex_lock(&inode->i_mutex);
> +
> +	ret = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
> +	if (ret)
> +		goto out;
> +
> +	if (gfs2_is_stuffed(ip)) {
> +		u64 phys = ip->i_no_addr << inode->i_blkbits;
> +		u64 size = i_size_read(inode);

It's actually safe to directly access i_size inside i_mutex.  Although
not terribly maintainable.


> +		u32 flags = FIEMAP_EXTENT_LAST|FIEMAP_EXTENT_NOT_ALIGNED|
> +			    FIEMAP_EXTENT_DATA_INLINE;
> +		phys += sizeof(struct gfs2_dinode);
> +		phys += start;
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