linux-kernel - Re: [PATCH] f2fs: fix to remove F2FS_COMPR_FL and tag F2FS_NOCOMP

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Date:   Thu, 23 Jun 2022 12:44:40 +0800
From:   Chao Liu <chaoliu719@...il.com>
To:     Chao Yu <chao@...nel.org>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Yue Hu <huyue2@...lpad.com>,
        Wayne Zhang <zhangwen@...lpad.com>,
        Xiaoyu Qi <qxy65535@...il.com>, Chao Liu <liuchao@...lpad.com>
Subject: Re: [PATCH] f2fs: fix to remove F2FS_COMPR_FL and tag F2FS_NOCOMP_FL
 at the same time

On Wed, Jun 22, 2022 at 09:42:13PM +0800, Chao Yu wrote:
> On 2022/6/21 14:48, Chao Liu wrote:
> > From: Chao Liu <liuchao@...lpad.com>
> >
> > If the inode has the compress flag, it will fail to use
> > 'chattr -c +m' to remove its compress flag and tag no compress flag.
> > However, the same command will be successful when executed again,
> > as shown below:
> >
> >    $ touch foo.txt
> >    $ chattr +c foo.txt
> >    $ chattr -c +m foo.txt
> >    chattr: Invalid argument while setting flags on foo.txt
> >    $ chattr -c +m foo.txt
> >    $ f2fs_io getflags foo.txt
> >    get a flag on foo.txt ret=0, flags=nocompression,inline_data
> >
> > Fix this by removing some checks in f2fs_setflags_common()
> > that do not affect the original logic. I go through all the
> > possible scenarios, and the results are as follows. Bold is
> > the only thing that has changed.
> >
> > +---------------+-----------+-----------+----------+
> > |               |            file flags            |
> > + command       +-----------+-----------+----------+
> > |               | no flag   | compr     | nocompr  |
> > +---------------+-----------+-----------+----------+
> > | chattr +c     | compr     | compr     | -EINVAL  |
> > | chattr -c     | no flag   | no flag   | nocompr  |
> > | chattr +m     | nocompr   | -EINVAL   | nocompr  |
> > | chattr -m     | no flag   | compr     | no flag  |
> > | chattr +c +m  | -EINVAL   | -EINVAL   | -EINVAL  |
> > | chattr +c -m  | compr     | compr     | compr    |
> > | chattr -c +m  | nocompr   | *nocompr* | nocompr  |
> > | chattr -c -m  | no flag   | no flag   | no flag  |
> > +---------------+-----------+-----------+----------+
> >
> > Fixes: 4c8ff7095bef ("f2fs: support data compression")
> > Signed-off-by: Chao Liu <liuchao@...lpad.com>
> > ---
> >
> > This patch depends on the the patch
> > "f2fs: allow compression of files without blocks" sent earlier this day.
> >
> >   fs/f2fs/file.c | 9 +--------
> >   1 file changed, 1 insertion(+), 8 deletions(-)
> >
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index daaa0dfd2d2e..0c3ae5993b7a 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1873,10 +1873,7 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
> >   		if (masked_flags & F2FS_COMPR_FL) {
> >   			if (!f2fs_disable_compressed_file(inode))
> >   				return -EINVAL;
> > -		}
> > -		if (iflags & F2FS_NOCOMP_FL)
> > -			return -EINVAL;
> > -		if (iflags & F2FS_COMPR_FL) {
> > +		} else {
> >   			if (!f2fs_may_compress(inode))
> >   				return -EINVAL;
> >   			if (S_ISREG(inode->i_mode) && F2FS_HAS_BLOCKS(inode))
> > @@ -1885,10 +1882,6 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
> >   			set_compress_context(inode);
> >   		}
> >   	}
> > -	if ((iflags ^ masked_flags) & F2FS_NOCOMP_FL) {
> > -		if (masked_flags & F2FS_COMPR_FL)
> > -			return -EINVAL;
> > -	}
>
> Without above check condition, can we return -EINVAL for the case:
>
> chattr +c on file w/ nocompr flag
>
> |               | no flag   | compr     | nocompr  |
> +---------------+-----------+-----------+----------+
> | chattr +c     | compr     | compr     | *-EINVAL*  |

Yes, we can.

chattr(1) grabs flags via GETFLAGS, modifies the result,
and passes that to SETFLAGS. If we execute 'chattr +c'
on the file with nocompr flag, the iflags will
contain both compr and nocompr flags, then be refused by:

    if ((iflags & F2FS_COMPR_FL) && (iflags & F2FS_NOCOMP_FL))
        return -EINVAL;

In addition, if iflags has only compr flag, while masked_flags
has only nocompr flag for some reason
(either because of concurrency of chattr(1) or by a user),
I think we need remove nocompr flag and tag compr flag on the file,
similar to the following.

|               | no flag   | compr     | nocompr  |
+---------------+-----------+-----------+----------+
| chattr +c -m  | compr     | compr     | *compr*  |

Thanks,