CIFS: Migrate to shared superblock model

Add cifs_match_super to use in sget to share superblock between mounts
that have the same //server/sharename, credentials and mount options.
It helps us to improve performance on work with future SMB2.1 leases.

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsfs.c

@@ -630,6 +630,7 @@ cifs_do_mount(struct file_system_type *fs_type,
 	struct super_block *sb;
 	struct cifs_sb_info *cifs_sb;
 	struct smb_vol *volume_info;
+	struct cifs_mnt_data mnt_data;
 	struct dentry *root;
 
 	cFYI(1, "Devname: %s flags: %d ", dev_name, flags);
@@ -646,12 +647,21 @@ cifs_do_mount(struct file_system_type *fs_type,
 
 	cifs_setup_cifs_sb(volume_info, cifs_sb);
 
-	sb = sget(fs_type, NULL, set_anon_super, NULL);
+	mnt_data.vol = volume_info;
+	mnt_data.cifs_sb = cifs_sb;
+	mnt_data.flags = flags;
+
+	sb = sget(fs_type, cifs_match_super, set_anon_super, &mnt_data);
 	if (IS_ERR(sb)) {
 		root = ERR_CAST(sb);
 		goto out_cifs_sb;
 	}
 
+	if (sb->s_fs_info) {
+		cFYI(1, "Use existing superblock");
+		goto out_shared;
+	}
+
 	/*
 	 * Copy mount params for use in submounts. Better to do
 	 * the copy here and deal with the error before cleanup gets
@@ -680,9 +690,16 @@ cifs_do_mount(struct file_system_type *fs_type,
 	root = cifs_get_root(volume_info, sb);
 	if (root == NULL)
 		goto out_super;
+
 	cFYI(1, "dentry root is: %p", root);
 	goto out;
 
+out_shared:
+	root = cifs_get_root(volume_info, sb);
+	if (root)
+		cFYI(1, "dentry root is: %p", root);
+	goto out;
+
 out_super:
 	kfree(cifs_sb->mountdata);
 	deactivate_locked_super(sb);

fs/cifs/cifsglob.h

@@ -210,6 +210,25 @@ struct smb_vol {
 	struct nls_table *local_nls;
 };
 
+#define CIFS_MOUNT_MASK (CIFS_MOUNT_NO_PERM | CIFS_MOUNT_SET_UID | \
+			 CIFS_MOUNT_SERVER_INUM | CIFS_MOUNT_DIRECT_IO | \
+			 CIFS_MOUNT_NO_XATTR | CIFS_MOUNT_MAP_SPECIAL_CHR | \
+			 CIFS_MOUNT_UNX_EMUL | CIFS_MOUNT_NO_BRL | \
+			 CIFS_MOUNT_CIFS_ACL | CIFS_MOUNT_OVERR_UID | \
+			 CIFS_MOUNT_OVERR_GID | CIFS_MOUNT_DYNPERM | \
+			 CIFS_MOUNT_NOPOSIXBRL | CIFS_MOUNT_NOSSYNC | \
+			 CIFS_MOUNT_FSCACHE | CIFS_MOUNT_MF_SYMLINKS | \
+			 CIFS_MOUNT_MULTIUSER | CIFS_MOUNT_STRICT_IO)
+
+#define CIFS_MS_MASK (MS_RDONLY | MS_MANDLOCK | MS_NOEXEC | MS_NOSUID | \
+		      MS_NODEV | MS_SYNCHRONOUS)
+
+struct cifs_mnt_data {
+	struct cifs_sb_info *cifs_sb;
+	struct smb_vol *vol;
+	int flags;
+};
+
 struct TCP_Server_Info {
 	struct list_head tcp_ses_list;
 	struct list_head smb_ses_list;

fs/cifs/connect.c

@@ -2146,6 +2146,100 @@ cifs_put_tlink(struct tcon_link *tlink)
 	return;
 }
 
+static inline struct tcon_link *
+cifs_sb_master_tlink(struct cifs_sb_info *cifs_sb);
+
+static int
+compare_mount_options(struct super_block *sb, struct cifs_mnt_data *mnt_data)
+{
+	struct cifs_sb_info *old = CIFS_SB(sb);
+	struct cifs_sb_info *new = mnt_data->cifs_sb;
+
+	if ((sb->s_flags & CIFS_MS_MASK) != (mnt_data->flags & CIFS_MS_MASK))
+		return 0;
+
+	if ((old->mnt_cifs_flags & CIFS_MOUNT_MASK) !=
+	    (new->mnt_cifs_flags & CIFS_MOUNT_MASK))
+		return 0;
+
+	if (old->rsize != new->rsize)
+		return 0;
+
+	/*
+	 * We want to share sb only if we don't specify wsize or specified wsize
+	 * is greater or equal than existing one.
+	 */
+	if (new->wsize && new->wsize < old->wsize)
+		return 0;
+
+	if (old->mnt_uid != new->mnt_uid || old->mnt_gid != new->mnt_gid)
+		return 0;
+
+	if (old->mnt_file_mode != new->mnt_file_mode ||
+	    old->mnt_dir_mode != new->mnt_dir_mode)
+		return 0;
+
+	if (strcmp(old->local_nls->charset, new->local_nls->charset))
+		return 0;
+
+	if (old->actimeo != new->actimeo)
+		return 0;
+
+	return 1;
+}
+
+int
+cifs_match_super(struct super_block *sb, void *data)
+{
+	struct cifs_mnt_data *mnt_data = (struct cifs_mnt_data *)data;
+	struct smb_vol *volume_info;
+	struct cifs_sb_info *cifs_sb;
+	struct TCP_Server_Info *tcp_srv;
+	struct cifsSesInfo *ses;
+	struct cifsTconInfo *tcon;
+	struct tcon_link *tlink;
+	struct sockaddr_storage addr;
+	int rc = 0;
+
+	memset(&addr, 0, sizeof(struct sockaddr_storage));
+
+	spin_lock(&cifs_tcp_ses_lock);
+	cifs_sb = CIFS_SB(sb);
+	tlink = cifs_get_tlink(cifs_sb_master_tlink(cifs_sb));
+	if (IS_ERR(tlink)) {
+		spin_unlock(&cifs_tcp_ses_lock);
+		return rc;
+	}
+	tcon = tlink_tcon(tlink);
+	ses = tcon->ses;
+	tcp_srv = ses->server;
+
+	volume_info = mnt_data->vol;
+
+	if (!volume_info->UNCip || !volume_info->UNC)
+		goto out;
+
+	rc = cifs_fill_sockaddr((struct sockaddr *)&addr,
+				volume_info->UNCip,
+				strlen(volume_info->UNCip),
+				volume_info->port);
+	if (!rc)
+		goto out;
+
+	if (!match_server(tcp_srv, (struct sockaddr *)&addr, volume_info) ||
+	    !match_session(ses, volume_info) ||
+	    !match_tcon(tcon, volume_info->UNC)) {
+		rc = 0;
+		goto out;
+	}
+
+	rc = compare_mount_options(sb, mnt_data);
+out:
+	cifs_put_tlink(tlink);
+	spin_unlock(&cifs_tcp_ses_lock);
+	return rc;
+}
+
 int
 get_dfs_path(int xid, struct cifsSesInfo *pSesInfo, const char *old_path,
 	     const struct nls_table *nls_codepage, unsigned int *pnum_referrals,
@@ -2578,6 +2672,14 @@ void cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
 		/* Windows ME may prefer this */
 		cFYI(1, "readsize set to minimum: 2048");
 	}
+
+	/*
+	 * Temporarily set wsize for matching superblock. If we end up using
+	 * new sb then cifs_negotiate_wsize will later negotiate it downward
+	 * if needed.
+	 */
+	cifs_sb->wsize = pvolume_info->wsize;
+
 	cifs_sb->mnt_uid = pvolume_info->linux_uid;
 	cifs_sb->mnt_gid = pvolume_info->linux_gid;
 	cifs_sb->mnt_file_mode = pvolume_info->file_mode;