fs/9p: v9fs_stat2inode should update suid/sgid bits.

Create a new helper that update the permission bits and use
that, instead of opencoding the logic.

Reported and bisected by: M. Mohan Kumar <[e-mail]>
Signed-off-by: Aneesh Kumar K.V <[e-mail]>
Signed-off-by: Eric Van Hensbergen <[e-mail]>

fs/9p/vfs_inode.c

···
 }
 
 /**
+ * p9mode2perm- convert plan9 mode bits to unix permission bits
+ * @v9ses: v9fs session information
+ * @stat: p9_wstat from which mode need to be derived
+ *
+ */
+static int p9mode2perm(struct v9fs_session_info *v9ses,
+		       struct p9_wstat *stat)
+{
+	int res;
+	int mode = stat->mode;
+
+	res = mode & S_IALLUGO;
+	if (v9fs_proto_dotu(v9ses)) {
+		if ((mode & P9_DMSETUID) == P9_DMSETUID)
+			res |= S_ISUID;
+
+		if ((mode & P9_DMSETGID) == P9_DMSETGID)
+			res |= S_ISGID;
+
+		if ((mode & P9_DMSETVTX) == P9_DMSETVTX)
+			res |= S_ISVTX;
+	}
+	return res;
+}
+
+/**
  * p9mode2unixmode- convert plan9 mode bits to unix mode bits
  * @v9ses: v9fs session information
  * @stat: p9_wstat from which mode need to be derived
···
 	int res;
 	int mode = stat->mode;
 
-	res = mode & S_IALLUGO;
 	*rdev = 0;
+	res = p9mode2perm(v9ses, stat);
 
 	if ((mode & P9_DMDIR) == P9_DMDIR)
 		res |= S_IFDIR;
···
 	} else
 		res |= S_IFREG;
 
-	if (v9fs_proto_dotu(v9ses)) {
-		if ((mode & P9_DMSETUID) == P9_DMSETUID)
-			res |= S_ISUID;
-
-		if ((mode & P9_DMSETGID) == P9_DMSETGID)
-			res |= S_ISGID;
-
-		if ((mode & P9_DMSETVTX) == P9_DMSETVTX)
-			res |= S_ISVTX;
-	}
 	return res;
 }
 
···
 				set_nlink(inode, i_nlink);
 		}
 	}
-	mode = stat->mode & S_IALLUGO;
+	mode = p9mode2perm(v9ses, stat);
 	mode |= inode->i_mode & ~S_IALLUGO;
 	inode->i_mode = mode;
 	i_size_write(inode, stat->length);