linux-kernel - Re: [git pull] vfs pile 1

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Message-ID: <20140130152636.GB12687@quack.suse.cz>
Date:	Thu, 30 Jan 2014 16:26:36 +0100
From:	Jan Kara <jack@...e.cz>
To:	Kim Jaegeuk <jaegeuk.kim@...il.com>
Cc:	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Jaegeuk Kim <jaegeuk.kim@...sung.com>
Subject: Re: [git pull] vfs pile 1

On Thu 30-01-14 11:02:49, Kim Jaegeuk wrote:
> 2014-01-29 Jan Kara <jack@...e.cz>:
> > On Tue 28-01-14 19:26:08, Linus Torvalds wrote:
> >> On Mon, Jan 27, 2014 at 6:25 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >> >         Assorted stuff; the biggest pile here is Christoph's ACL series.
> >> > Plus assorted cleanups and fixes all over the place...  There will be
> >> > another pile later this week.
> >>
> >> The posix_acl_chmod() code looks wrong.
> >>
> >> Not that it looked right before either, but whatever. The code
> >> basically looks like some variation of this in most setattr()
> >> implementations:
> >>
> >>         if (ia_valid & ATTR_MODE)
> >>                 rc = posix_acl_chmod(inode, inode->i_mode);
> >>
> >> but the mode we're changing to (and what ATTR_MODE guards) is actually
> >> attr->ia_mode, not inode->i_mode.
> >   Yes, but posix_acl_chmod() is called after setattr_copy() was done so
> > inode->i_mode should be the same as attr->ia_mode. Whether i_mode or
> > ia_mode is mode logical depends on whether you view posix_acl_chmod() as
> > "sync current i_mode into acls" or "reflect this i_mode change in acls".
> > I agree the function name suggests more the latter semantics.
> >
> >> And quite frankly, passing in inode->i_mode looks stupid, since we're
> >> already passing in the inode pointer, so that's just redundant and
> >> pointless information.
> >   Yes, it looks stupid. We could almost drop that argument, except that f2fs
> > tries to play some tricks with i_mode and stores i_mode in a different
> > place when acls are enabled. Huh? Jaegeuk, can you explain why are you
> > doing that?
> 
> As described to Christoph before, the reason is for acl consistency
> between on-disk xattr->mode and on-disk inode->mode.
> 
> Previously, there are three i_modes managed by:
>                        inode->mode   on-disk xattr->mode  on-disk->i_mode
> f2fs_setattr            [x]                       y                       y
> [update_inode]       x                        y                      [x]
> [checkpoint]            x                       [y]                      x
> __f2fs_setxattr        x                       [x]                      x
> 
> In this flow, f2fs is able to break the consistency between on-disk
> xattr->mode and on-disk->i_mode after checkpoint followed by
> sudden-power-off.
> 
> So, fi->i_mode was introduced to address the problem.
> The new f2fs_setattr triggers:
>                 inode->mode   fi->i_mode  on-disk xattr->mode  on-disk->i_mode
> f2fs_setattr             y                [x]                     y
>                       y
> [update_inode]       y                 x                      y
>                   y
> [checkpoint]            y                 x                      y
>                      y
> __f2fs_setxattr       [x]                x                     [x]
>                    [x]
> 
> Finally, __f2fs_setxattr synchronizes inode->mode, on-disk xattr->mode,
> and on-disk inode->i_mode all together.
> 
> Am I missing something?
  OK, I see. Thanks for explanation.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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