On Dec 7, 2021, at 12:34 PM, Theodore Y. Ts'o <tytso@MIT.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?

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?

Cheers, Andreas