linux-ext4 - Re: [PATCH] ext4: compare inode's i_projid with EXT4_DEF_PROJID rather than check EXT4_INODE

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Date:   Fri, 10 Dec 2021 22:53:00 +0300 (MSK)
From:   Roman Anufriev <dotdot@...dex-team.ru>
To:     Andreas Dilger <adilger@...ger.ca>
cc:     "Theodore Y. Ts'o" <tytso@....EDU>, david@...morbit.com,
        linux-ext4 <linux-ext4@...r.kernel.org>, Jan Kara <jack@...e.cz>,
        Wang Shilong <wangshilong1991@...il.com>,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>,
        "Darrick J. Wong" <darrick.wong@...cle.com>
Subject: Re: [PATCH] ext4: compare inode's i_projid with EXT4_DEF_PROJID
 rather than check EXT4_INODE_PROJINHERIT flag


On Thu, 9 Dec 2021, Andreas Dilger wrote:

> On Dec 7, 2021, at 12:34 PM, Theodore Y. Ts'o <tytso@....EDU> wrote:
>>
>> On Tue, Dec 07, 2021 at 05:05:19PM +0300, Roman Anufriev wrote:
>>>> Commit 7ddf79a10395 ("ext4: only set project inherit bit for directory")
>>>> removes EXT4_INODE_PROJINHERIT flag from regular files. This makes
>>>> ext4_statfs() output incorrect (function does not apply quota limits
>>>> on used/available space, etc) when called on dentry of regular file
>>>> with project quota enabled.
>>
>> Under what circumstance is userspace trying to call statfs on a file
>> descriptor?
>
> Who knows what users do?  Calling statfs() on a regular file works fine
> (returns stats for the filesystem), so I don't see why it wouldn't be
> consistent when calling statfs() on a file with projid set?

This is exactly my reasoning for this patch.

> Darrick, how does XFS handle this case?  I think it makes sense to be
> consistent with that implementation, since that was the main reason to
> remove PROJINHERIT from regular files in the first place.
>
>> Removing the test for EXT4_INODE_PROJINHERIT will cause
>> incorrect/misleading results being returned in the case where we have
>> a directory where a directory hierarchy is using project id's, but
>> which is *not* using PROJINHERIT.
>
> One alternative would be to check the PROJINHERIT status of the parent
> directory after calling statfs() on the regular file?  That should
> keep the semantics for PROJINHERIT the same, but avoid inconsistent
> results if called on a regular file:
>
> #ifdef CONFIG_QUOTA
> -	if (ext4_test_inode_flag(dentry->d_inode, EXT4_INODE_PROJINHERIT) &&
> +	if (ext4_test_inode_flag(S_ISDIR(dentry->d_inode) ? dentry->d_inode :
> +			   dentry->d_parent->d_inode, EXT4_INODE_PROJINHERIT) &&
> 	    sb_has_quota_limits_enabled(sb, PRJQUOTA))
> 		ext4_statfs_project(sb, EXT4_I(dentry->d_inode)->i_projid, buf);
> #endif
>
> Roman, does that work for you?

Yes, it was actually the first thing that came to my mind. But later I
realised, that there may be some pitfalls and it would probably make more
sense to check inode's own project id and report stats based on that. As
I thought that we check presense of EXT4_INODE_PROJINHERIT flag only to
make sure that this inode belongs to some project.

 								Roman