[PATCH 3/4] xfs: allow setting xattrs on special files

[Andrey Albershteyn <aalbersh@redhat.com>]

As XFS didn't have ioctls for special files setting an inode
extended attributes was rejected for them in xfs_fileattr_set().
Same applies for reading.

With XFS's project quota directories this is necessary. When project
is setup, xfs_quota opens and calls FS_IOC_SETFSXATTR on every inode
in the directory. However, special files are skipped due to open()
returning a special inode for them. So, they don't even get to this
check.

The further patch introduces XFS_IOC_SETFSXATTRAT which will call
xfs_fileattr_set/get() on a special file. This patch add handling of
setting xflags and project ID for special files.

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
 fs/xfs/xfs_ioctl.c | 96 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 92 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index f0117188f302..515c9b4b862d 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -459,9 +459,6 @@ xfs_fileattr_get(
 {
 	struct xfs_inode	*ip = XFS_I(d_inode(dentry));
 
-	if (d_is_special(dentry))
-		return -ENOTTY;
-
 	xfs_ilock(ip, XFS_ILOCK_SHARED);
 	xfs_fill_fsxattr(ip, XFS_DATA_FORK, fa);
 	xfs_iunlock(ip, XFS_ILOCK_SHARED);
@@ -721,6 +718,97 @@ xfs_ioctl_setattr_check_projid(
 	return 0;
 }
 
+static int
+xfs_fileattr_spec_set(
+	struct mnt_idmap	*idmap,
+	struct dentry		*dentry,
+	struct fileattr		*fa)
+{
+	struct xfs_inode *ip = XFS_I(d_inode(dentry));
+	struct xfs_mount *mp = ip->i_mount;
+	struct xfs_trans *tp;
+	struct xfs_dquot *pdqp = NULL;
+	struct xfs_dquot *olddquot = NULL;
+	int error;
+
+	if (!fa->fsx_valid)
+		return -EOPNOTSUPP;
+
+	if (fa->fsx_extsize ||
+	    fa->fsx_nextents ||
+	    fa->fsx_cowextsize)
+		return -EOPNOTSUPP;
+
+	error = xfs_ioctl_setattr_check_projid(ip, fa);
+	if (error)
+		return error;
+
+	/*
+	 * If disk quotas is on, we make sure that the dquots do exist on disk,
+	 * before we start any other transactions. Trying to do this later
+	 * is messy. We don't care to take a readlock to look at the ids
+	 * in inode here, because we can't hold it across the trans_reserve.
+	 * If the IDs do change before we take the ilock, we're covered
+	 * because the i_*dquot fields will get updated anyway.
+	 */
+	if (fa->fsx_valid && XFS_IS_QUOTA_ON(mp)) {
+		error = xfs_qm_vop_dqalloc(ip, VFS_I(ip)->i_uid,
+					   VFS_I(ip)->i_gid, fa->fsx_projid,
+					   XFS_QMOPT_PQUOTA, NULL, NULL, &pdqp);
+		if (error)
+			return error;
+	}
+
+	tp = xfs_ioctl_setattr_get_trans(ip, pdqp);
+	if (IS_ERR(tp)) {
+		error = PTR_ERR(tp);
+		goto error_free_dquots;
+	}
+
+	error = xfs_ioctl_setattr_xflags(tp, ip, fa);
+	if (error)
+		goto error_trans_cancel;
+
+	/*
+	 * Change file ownership.  Must be the owner or privileged.  CAP_FSETID
+	 * overrides the following restrictions:
+	 *
+	 * The set-user-ID and set-group-ID bits of a file will be cleared upon
+	 * successful return from chown()
+	 */
+
+	if ((VFS_I(ip)->i_mode & (S_ISUID | S_ISGID)) &&
+	    !capable_wrt_inode_uidgid(idmap, VFS_I(ip), CAP_FSETID))
+		VFS_I(ip)->i_mode &= ~(S_ISUID | S_ISGID);
+
+	/* Change the ownerships and register project quota modifications */
+	if (ip->i_projid != fa->fsx_projid) {
+		if (XFS_IS_PQUOTA_ON(mp)) {
+			olddquot =
+				xfs_qm_vop_chown(tp, ip, &ip->i_pdquot, pdqp);
+		}
+		ip->i_projid = fa->fsx_projid;
+	}
+
+	error = xfs_trans_commit(tp);
+
+	/*
+	 * Release any dquot(s) the inode had kept before chown.
+	 */
+	xfs_qm_dqrele(olddquot);
+	xfs_qm_dqrele(pdqp);
+
+	return error;
+
+error_trans_cancel:
+	xfs_trans_cancel(tp);
+error_free_dquots:
+	xfs_qm_dqrele(pdqp);
+	return error;
+
+	return 0;
+}
+
 int
 xfs_fileattr_set(
 	struct mnt_idmap	*idmap,
@@ -737,7 +825,7 @@ xfs_fileattr_set(
 	trace_xfs_ioctl_setattr(ip);
 
 	if (d_is_special(dentry))
-		return -ENOTTY;
+		return xfs_fileattr_spec_set(idmap, dentry, fa);
 
 	if (!fa->fsx_valid) {
 		if (fa->flags & ~(FS_IMMUTABLE_FL | FS_APPEND_FL |
-- 
2.42.0