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Date:   Fri, 7 Jun 2019 11:14:52 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Wang Shilong <wshilong@ddn.com>
Cc:     Wang Shilong <wangshilong1991@gmail.com>,
        "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
        "linux-f2fs-devel@lists.sourceforge.net" 
        <linux-f2fs-devel@lists.sourceforge.net>,
        Andreas Dilger <adilger@dilger.ca>
Subject: Re: =?utf-8?B?5Zue5aSNOiBbZjJmcy1kZXZdIFtQ?= =?utf-8?Q?ATCH?= 1/2]
 ext4: only set project inherit bit for directory
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On Fri, Jun 07, 2019 at 07:51:18AM +0000, Wang Shilong wrote:
> Hi,
> 
> > --
> > 2.21.0
> 
> Won't this break 'chattr' on files that already have this flag set?
> FS_IOC_GETFLAGS will return this flag, so 'chattr' will pass it back to
> FS_IOC_SETFLAGS which will return EOPNOTSUPP due to this:
> 
> ? ? ? ? if (ext4_mask_flags(inode->i_mode, flags) != flags)
> ? ? ? ? ? ? ? ? return -EOPNOTSUPP;
> 
> >>>>
> 
> You are right for this and we also need take care of this in EXT4_IOC_FSSETXATTR/
> this is a bit strange behavior as chattr read existed flags
> but could not set them again, there are several possible ways that I could think
> of to fix the issue?
> 
> 1) change chattr to filter Project inherit bit before call FS_IOC_SETFLAGS
> 
> 2) we automatically fixed the flag before mask check, something like:
> if reg:
>      flags &= ~PROJECT_INHERT;
>       if (ext4_mask_flags(inode->i_mode, flags) != flags)
> ? ? ? ? ? ? ? ? return -EOPNOTSUPP;
> But this might be not good..
> 
> I would prefer solution 1)
> What do you think?

Existing versions of chattr can't be changed, and people don't necessarily
upgrade the kernel and e2fsprogs at the same time.  So (1) wouldn't really work.

A better solution might be to make FS_IOC_GETFLAGS and FS_IOC_FSGETXATTR never
return the project inherit flag on regular files.

- Eric