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Date: Sat, 15 Jun 2013 13:09:18 +0800
From: Jeff Liu <jeff.liu@...cle.com>
To: Richard Yao <ryao@...too.org>
CC: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel@...too.org, Ocfs2-Devel <ocfs2-devel@....oracle.com>,
Joel Becker <jlbec@...lplan.org>,
Mark Fasheh <mfasheh@...e.com>
Subject: Re: [PATCH 1/2] ocfs2: Fix llseek() semantics and do some cleanup
[Add ocfs2-devel to CC-list]
Hello Richard,
Thanks for your patch.
On 06/15/2013 03:23 AM, Richard Yao wrote:
> There are multiple issues with the custom llseek implemented in ocfs2 for
> implementing SEEK_HOLE/SEEK_DATA.
>
> 1. It takes the inode->i_mutex lock before calling generic_file_llseek(), which
> is unnecessary.
Agree, but please see my comments below.
>
> 2. It fails to take the filp->f_lock spinlock before modifying filp->f_pos and
> filp->f_version, which differs from generic_file_llseek().
>
> 3. It does a offset > inode->i_sb->s_maxbytes check that permits seeking up to
> the maximum file size possible on the ocfs2 filesystem, even when it is past
> the end of the file. Seeking beyond that (if possible), would return EINVAL
> instead of ENXIO.
>
> 4. The switch statement tries to cover all whence values when in reality it
> should only care about SEEK_HOLE/SEEK_DATA. Any other cases should be passsed
> to generic_file_llseek().
I have another patch set for refactoring ocfs2_file_llseek() but not yet found time
to run a comprehensive tests. It can solve the existing issues but also improved the
SEEK_DATA/SEEK_HOLE for unwritten extents, i.e. OCFS2_EXT_UNWRITTEN.
With this change, SEEK_DATA/SEEK_HOLE will go into separate function with a little code
duplication instead of the current mix-ups in ocfs2_seek_data_hole_offset(), i.e,
loff_t ocfs2_file_llseek()
{
switch (origin) {
case SEEK_END:
case SEEK_CUR:
case SEEK_SET:
return generic_file_llseek(file, offset, origin);
case SEEK_DATA:
return ocfs2_seek_data(file, offset);
case SEEK_HOLE:
return ocfs2_seek_hole(file, offset);
default:
return -EINVAL;
}
}
I personally like keeping SEEK_DATA/SEEK_HOLE in switch...case style rather
than dealing with them in a condition check block.
Thanks,
-Jeff
>
> btrfs_file_llseek() and ocfs2_file_llseek() are extremely similar and
> consequently, contain many of the same flaws. Li Dongyang filed a pull
> request with ZFSOnLinux for SEEK_HOLE/SEEK_DATA support that included a
> custom llseek function that appears to have been modelled after the one
> in ocfs2. The similarity was strong enough that it suffered from many of
> the same flaws, which I caught during review. I addressed the issues
> with his patch with one that I wrote. Since a small percentage of Gentoo
> Linux users are affected by these flaws, I decided to adapt that code
> that to btrfs (separate patch) and ocfs2.
>
> Note that commit 48802c8ae2a9d618ec734a61283d645ad527e06c by Jeff Liu at
> Oracle mostly addressed #3 in btrfs. The only lingering issue was that
> the offset > inode->i_sb->s_maxbytes check became dead code. The ocfs2
> code was not fortunate enough to have had a similar correction until
> now.
>
> Signed-off-by: Richard Yao <ryao@...too.org>
> ---
> fs/ocfs2/file.c | 65 ++++++++++++++++++++++-----------------------------------
> 1 file changed, 25 insertions(+), 40 deletions(-)
>
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index ff54014..84f8c9c 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2615,54 +2615,39 @@ bail:
> }
>
> /* Refer generic_file_llseek_unlocked() */
> -static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int whence)
> +static loff_t ocfs2_file_llseek(struct file *filp, loff_t offset, int whence)
> {
> - struct inode *inode = file->f_mapping->host;
> - int ret = 0;
> + if (whence == SEEK_DATA || whence == SEEK_HOLE) {
> + struct inode *inode = filp->f_mapping->host;
> + int ret;
>
> - mutex_lock(&inode->i_mutex);
> + if (offset < 0 && !(filp->f_mode & FMODE_UNSIGNED_OFFSET))
> + return -EINVAL;
>
> - switch (whence) {
> - case SEEK_SET:
> - break;
> - case SEEK_END:
> - offset += inode->i_size;
> - break;
> - case SEEK_CUR:
> - if (offset == 0) {
> - offset = file->f_pos;
> - goto out;
> + if (offset >= i_size_read(inode)) {
> + return -ENXIO;
> }
> - offset += file->f_pos;
> - break;
> - case SEEK_DATA:
> - case SEEK_HOLE:
> - ret = ocfs2_seek_data_hole_offset(file, &offset, whence);
> - if (ret)
> - goto out;
> - break;
> - default:
> - ret = -EINVAL;
> - goto out;
> - }
>
> - if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET))
> - ret = -EINVAL;
> - if (!ret && offset > inode->i_sb->s_maxbytes)
> - ret = -EINVAL;
> - if (ret)
> - goto out;
> + mutex_lock(&inode->i_mutex);
> + ret = ocfs2_seek_data_hole_offset(filp, &offset, whence);
> + mutex_unlock(&inode->i_mutex);
> +
> + if (ret) {
> + return ret;
> + }
>
> - if (offset != file->f_pos) {
> - file->f_pos = offset;
> - file->f_version = 0;
> + if (offset != filp->f_pos) {
> + spin_lock(&filp->f_lock);
> + filp->f_pos = offset;
> + filp->f_version = 0;
> + spin_unlock(&filp->f_lock);
> + }
> +
> + return offset;
> }
>
> -out:
> - mutex_unlock(&inode->i_mutex);
> - if (ret)
> - return ret;
> - return offset;
> + return generic_file_llseek(filp, offset, whence);
> +
> }
>
> const struct inode_operations ocfs2_file_iops = {
--
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