smb3: fix creating FIFOs when mounting with "sfu" mount option

Fixes some xfstests including generic/564 and generic/157

The "sfu" mount option can be useful for creating special files (character
and block devices in particular) but could not create FIFOs. It did
recognize existing empty files with the "system" attribute flag as FIFOs
but this is too general, so to support creating FIFOs more safely use a new
tag (but the same length as those for char and block devices ie "IntxLNK"
and "IntxBLK") "LnxFIFO" to indicate that the file should be treated as a
FIFO (when mounted with the "sfu").   For some additional context note that
"sfu" followed the way that "Services for Unix" on Windows handled these
special files (at least for character and block devices and symlinks),
which is different than newer Windows which can handle special files
as reparse points (which isn't an option to many servers).

Cc: stable@vger.kernel.org
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/cifspdu.h

@@ -2570,7 +2570,7 @@ typedef struct {
 
 
 struct win_dev {
-	unsigned char type[8]; /* IntxCHR or IntxBLK */
+	unsigned char type[8]; /* IntxCHR or IntxBLK or LnxFIFO*/
 	__le64 major;
 	__le64 minor;
 } __attribute__((packed));

fs/smb/client/inode.c

@@ -592,6 +592,10 @@ cifs_sfu_type(struct cifs_fattr *fattr, const char *path,
 			cifs_dbg(FYI, "Symlink\n");
 			fattr->cf_mode |= S_IFLNK;
 			fattr->cf_dtype = DT_LNK;
+		} else if (memcmp("LnxFIFO", pbuf, 8) == 0) {
+			cifs_dbg(FYI, "FIFO\n");
+			fattr->cf_mode |= S_IFIFO;
+			fattr->cf_dtype = DT_FIFO;
 		} else {
 			fattr->cf_mode |= S_IFREG; /* file? */
 			fattr->cf_dtype = DT_REG;

fs/smb/client/smb2ops.c

@@ -5087,7 +5087,7 @@ smb2_make_node(unsigned int xid, struct inode *inode,
 	 * over SMB2/SMB3 and Samba will do this with SMB3.1.1 POSIX Extensions
 	 */
 
-	if (!S_ISCHR(mode) && !S_ISBLK(mode))
+	if (!S_ISCHR(mode) && !S_ISBLK(mode) && !S_ISFIFO(mode))
 		return rc;
 
 	cifs_dbg(FYI, "sfu compat create special file\n");
@@ -5135,6 +5135,12 @@ smb2_make_node(unsigned int xid, struct inode *inode,
 		pdev->minor = cpu_to_le64(MINOR(dev));
 		rc = tcon->ses->server->ops->sync_write(xid, &fid, &io_parms,
 							&bytes_written, iov, 1);
+	} else if (S_ISFIFO(mode)) {
+		memcpy(pdev->type, "LnxFIFO", 8);
+		pdev->major = 0;
+		pdev->minor = 0;
+		rc = tcon->ses->server->ops->sync_write(xid, &fid, &io_parms,
+							&bytes_written, iov, 1);
 	}
 	tcon->ses->server->ops->close(xid, tcon, &fid);
 	d_drop(dentry);