Re: [PATCH v2] xfs: allow cross-linking special files without project quota

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On 2024-03-14 19:48:26, Darrick J. Wong wrote:
> On Thu, Mar 14, 2024 at 06:07:02PM +0100, Andrey Albershteyn wrote:
> > There's an issue that if special files is created before quota
> > project is enabled, then it's not possible to link this file. This
> > works fine for normal files. This happens because xfs_quota skips
> > special files (no ioctls to set necessary flags). The check for
> > having the same project ID for source and destination then fails as
> > source file doesn't have any ID.
> > 
> > mkfs.xfs -f /dev/sda
> > mount -o prjquota /dev/sda /mnt/test
> > 
> > mkdir /mnt/test/foo
> > mkfifo /mnt/test/foo/fifo1
> > 
> > xfs_quota -xc "project -sp /mnt/test/foo 9" /mnt/test
> > > Setting up project 9 (path /mnt/test/foo)...
> > > xfs_quota: skipping special file /mnt/test/foo/fifo1
> > > Processed 1 (/etc/projects and cmdline) paths for project 9 with recursion depth infinite (-1).
> > 
> > ln /mnt/test/foo/fifo1 /mnt/test/foo/fifo1_link
> > > ln: failed to create hard link '/mnt/test/testdir/fifo1_link' => '/mnt/test/testdir/fifo1': Invalid cross-device link
> 
> Aha.  So hardlinking special files within a directory subtree that all
> have the same nonzero project quota ID fails if that special file
> happened to have been created before the subtree was assigned that pqid.
> And there's nothing we can do about that, because there's no way to call
> XFS_IOC_SETFSXATTR on a special file because opening those gets you a
> different inode from the special block/fifo/chardev filesystem...
> 
> > mkfifo /mnt/test/foo/fifo2
> > ln /mnt/test/foo/fifo2 /mnt/test/foo/fifo2_link
> > 
> > Fix this by allowing linking of special files to the project quota
> > if special files doesn't have any ID set (ID = 0).
> 
> ...and that's the workaround for this situation.  The project quota
> accounting here will be weird because there will be (more) files in a
> directory subtree than is reported by xfs_quota, but the subtree was
> already messed up in that manner.
> 
> Question: Should we have a XFS_IOC_SETFSXATTRAT where we can pass in
> relative directory paths and actually query/update special files?

After some more thinking/looking into the code this is probably the
only way to make it work the same for special files. Also, I've
noticed that this workaround can be applied to xfs_rename then.

So, I will start with implementing XFS_IOC_SETFSXATTRAT

-- 
- Andrey

> > Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
> 
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> 
> --D
> 
> > ---
> >  fs/xfs/xfs_inode.c | 15 +++++++++++++--
> >  1 file changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index 1fd94958aa97..b7be19be0132 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -1240,8 +1240,19 @@ xfs_link(
> >  	 */
> >  	if (unlikely((tdp->i_diflags & XFS_DIFLAG_PROJINHERIT) &&
> >  		     tdp->i_projid != sip->i_projid)) {
> > -		error = -EXDEV;
> > -		goto error_return;
> > +		/*
> > +		 * Project quota setup skips special files which can
> > +		 * leave inodes in a PROJINHERIT directory without a
> > +		 * project ID set. We need to allow links to be made
> > +		 * to these "project-less" inodes because userspace
> > +		 * expects them to succeed after project ID setup,
> > +		 * but everything else should be rejected.
> > +		 */
> > +		if (!special_file(VFS_I(sip)->i_mode) ||
> > +		    sip->i_projid != 0) {
> > +			error = -EXDEV;
> > +			goto error_return;
> > +		}
> >  	}
> >  
> >  	if (!resblks) {
> > -- 
> > 2.42.0
> > 
> > 
> 





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