cifs: add "mfsymlinks" mount option

This is the start for an implementation of "Minshall+French Symlinks"
(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks).

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/README

@@ -527,6 +527,11 @@ A partial list of the supported mount options follows:
 		SFU does).  In the future the bottom 9 bits of the
 		mode also will be emulated using queries of the security
 		descriptor (ACL).
+ mfsymlinks     Enable support for Minshall+French symlinks
+		(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
+		This option is ignored when specified together with the
+		'sfu' option. Minshall+French symlinks are used even if
+		the server supports the CIFS Unix Extensions.
  sign           Must use packet signing (helps avoid unwanted data modification
 		by intermediate systems in the route).  Note that signing
 		does not work with lanman or plaintext authentication.

fs/cifs/cifsfs.c

@@ -441,6 +441,8 @@ cifs_show_options(struct seq_file *s, struct vfsmount *m)
 		seq_printf(s, ",dynperm");
 	if (m->mnt_sb->s_flags & MS_POSIXACL)
 		seq_printf(s, ",acl");
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MF_SYMLINKS)
+		seq_printf(s, ",mfsymlinks");
 
 	seq_printf(s, ",rsize=%d", cifs_sb->rsize);
 	seq_printf(s, ",wsize=%d", cifs_sb->wsize);

fs/cifs/connect.c

@@ -100,6 +100,7 @@ struct smb_vol {
 	bool noautotune:1;
 	bool nostrictsync:1; /* do not force expensive SMBflush on every sync */
 	bool fsc:1;	/* enable fscache */
+	bool mfsymlinks:1; /* use Minshall+French Symlinks */
 	unsigned int rsize;
 	unsigned int wsize;
 	bool sockopt_tcp_nodelay:1;
@@ -1342,6 +1343,8 @@ cifs_parse_mount_options(char *options, const char *devname,
 				"/proc/fs/cifs/LookupCacheEnabled to 0\n");
 		} else if (strnicmp(data, "fsc", 3) == 0) {
 			vol->fsc = true;
+		} else if (strnicmp(data, "mfsymlinks", 10) == 0) {
+			vol->mfsymlinks = true;
 		} else
 			printk(KERN_WARNING "CIFS: Unknown mount option %s\n",
 						data);
@@ -2554,6 +2557,14 @@ static void setup_cifs_sb(struct smb_vol *pvolume_info,
 		cFYI(1, "mounting share using direct i/o");
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_DIRECT_IO;
 	}
+	if (pvolume_info->mfsymlinks) {
+		if (pvolume_info->sfu_emul) {
+			cERROR(1,  "mount option mfsymlinks ignored if sfu "
+				   "mount option is used");
+		} else {
+			cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_MF_SYMLINKS;
+		}
+	}
 
 	if ((pvolume_info->cifs_acl) && (pvolume_info->dynperm))
 		cERROR(1, "mount option dynperm ignored if cifsacl "