smb3: fix redundant opens on root

In SMB2/SMB3 unlike in cifs we unnecessarily open the root of the share
over and over again in various places during mount and path revalidation
and also in statfs.  This patch cuts redundant traffic (opens and closes)
by simply keeping the directory handle for the root around (and reopening
it as needed on reconnect), so query calls don't require three round
trips to copmlete - just one, and eases load on network, client and
server (on mount alone, cuts network traffic by more than a third).

Also add a new cifs mount parm "nohandlecache" to allow users whose
servers might have resource constraints (eg in case they have a server
with so many users connecting to it that this extra handle per mount
could possibly be a resource concern).
Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

fs/cifs/cifs_fs_sb.h

@@ -50,6 +50,7 @@
 					      * root mountable
 					      */
 #define CIFS_MOUNT_UID_FROM_ACL 0x2000000 /* try to get UID via special SID */
+#define CIFS_MOUNT_NO_HANDLE_CACHE 0x4000000 /* disable caching dir handles */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;

fs/cifs/cifsfs.c

@@ -495,6 +495,8 @@ cifs_show_options(struct seq_file *s, struct dentry *root)
 		seq_puts(s, ",sfu");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_BRL)
 		seq_puts(s, ",nobrl");
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_HANDLE_CACHE)
+		seq_puts(s, ",nohandlecache");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL)
 		seq_puts(s, ",cifsacl");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_DYNPERM)

fs/cifs/cifsglob.h

@@ -525,6 +525,7 @@ struct smb_vol {
 	bool nullauth:1;   /* attempt to authenticate with null user */
 	bool nocase:1;     /* request case insensitive filenames */
 	bool nobrl:1;      /* disable sending byte range locks to srv */
+	bool nohandlecache:1; /* disable caching dir handles if srvr probs */
 	bool mand_lock:1;  /* send mandatory not posix byte range lock reqs */
 	bool seal:1;       /* request transport encryption on share */
 	bool nodfs:1;      /* Do not request DFS, even if available */
@@ -953,6 +954,7 @@ struct cifs_tcon {
 	bool print:1; /* set if connection to printer share */
 	bool retry:1;
 	bool nocase:1;
+	bool nohandlecache:1; /* if strange server resource prob can turn off */
 	bool seal:1;      /* transport encryption for this mounted share */
 	bool unix_ext:1;  /* if false disable Linux extensions to CIFS protocol
 				for this mount even if server would support */
@@ -979,6 +981,9 @@ struct cifs_tcon {
 	struct fscache_cookie *fscache;	/* cookie for share */
 #endif
 	struct list_head pending_opens;	/* list of incomplete opens */
+	bool valid_root_fid:1;	/* Do we have a useable root fid */
+	struct mutex prfid_mutex; /* prevents reopen race after dead ses*/
+	struct cifs_fid *prfid;	/* handle to the directory at top of share */
 	/* BB add field for back pointer to sb struct(s)? */
 };
 

fs/cifs/cifssmb.c

@@ -106,6 +106,12 @@ cifs_mark_open_files_invalid(struct cifs_tcon *tcon)
 		open_file->oplock_break_cancelled = true;
 	}
 	spin_unlock(&tcon->open_file_lock);
+
+	mutex_lock(&tcon->prfid_mutex);
+	tcon->valid_root_fid = false;
+	memset(tcon->prfid, 0, sizeof(struct cifs_fid));
+	mutex_unlock(&tcon->prfid_mutex);
+
 	/*
 	 * BB Add call to invalidate_inodes(sb) for all superblocks mounted
 	 * to this tcon.

fs/cifs/connect.c

@@ -79,6 +79,7 @@ enum {
 	Opt_noposixpaths, Opt_nounix,
 	Opt_nocase,
 	Opt_brl, Opt_nobrl,
+	Opt_handlecache, Opt_nohandlecache,
 	Opt_forcemandatorylock, Opt_setuidfromacl, Opt_setuids,
 	Opt_nosetuids, Opt_dynperm, Opt_nodynperm,
 	Opt_nohard, Opt_nosoft,
@@ -148,6 +149,8 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_nocase, "ignorecase" },
 	{ Opt_brl, "brl" },
 	{ Opt_nobrl, "nobrl" },
+	{ Opt_handlecache, "handlecache" },
+	{ Opt_nohandlecache, "nohandlecache" },
 	{ Opt_nobrl, "nolock" },
 	{ Opt_forcemandatorylock, "forcemandatorylock" },
 	{ Opt_forcemandatorylock, "forcemand" },
@@ -1445,6 +1448,12 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 				(S_IALLUGO & ~(S_ISUID | S_IXGRP)))
 				vol->file_mode = S_IALLUGO;
 			break;
+		case Opt_nohandlecache:
+			vol->nohandlecache = 1;
+			break;
+		case Opt_handlecache:
+			vol->nohandlecache = 0;
+			break;
 		case Opt_forcemandatorylock:
 			vol->mand_lock = 1;
 			break;
@@ -3022,6 +3031,7 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 	 */
 	tcon->retry = volume_info->retry;
 	tcon->nocase = volume_info->nocase;
+	tcon->nohandlecache = volume_info->nohandlecache;
 	tcon->local_lease = volume_info->local_lease;
 	INIT_LIST_HEAD(&tcon->pending_opens);
 
@@ -3580,6 +3590,8 @@ int cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_UNX_EMUL;
 	if (pvolume_info->nobrl)
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_BRL;
+	if (pvolume_info->nohandlecache)
+		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_HANDLE_CACHE;
 	if (pvolume_info->nostrictsync)
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NOSSYNC;
 	if (pvolume_info->mand_lock)
@@ -4353,6 +4365,7 @@ cifs_construct_tcon(struct cifs_sb_info *cifs_sb, kuid_t fsuid)
 	vol_info->UNC = master_tcon->treeName;
 	vol_info->retry = master_tcon->retry;
 	vol_info->nocase = master_tcon->nocase;
+	vol_info->nohandlecache = master_tcon->nohandlecache;
 	vol_info->local_lease = master_tcon->local_lease;
 	vol_info->no_linux_ext = !master_tcon->unix_ext;
 	vol_info->sectype = master_tcon->ses->sectype;

fs/cifs/misc.c

@@ -117,6 +117,8 @@ tconInfoAlloc(void)
 		INIT_LIST_HEAD(&ret_buf->openFileList);
 		INIT_LIST_HEAD(&ret_buf->tcon_list);
 		spin_lock_init(&ret_buf->open_file_lock);
+		mutex_init(&ret_buf->prfid_mutex);
+		ret_buf->prfid = kzalloc(sizeof(struct cifs_fid), GFP_KERNEL);
 #ifdef CONFIG_CIFS_STATS
 		spin_lock_init(&ret_buf->stat_lock);
 #endif
@@ -134,6 +136,7 @@ tconInfoFree(struct cifs_tcon *buf_to_free)
 	atomic_dec(&tconInfoAllocCount);
 	kfree(buf_to_free->nativeFileSystem);
 	kzfree(buf_to_free->password);
+	kfree(buf_to_free->prfid);
 	kfree(buf_to_free);
 }
 

fs/cifs/smb2inode.c

@@ -44,11 +44,22 @@ smb2_open_op_close(const unsigned int xid, struct cifs_tcon *tcon,
 		   __u32 create_options, void *data, int command)
 {
 	int rc, tmprc = 0;
-	__le16 *utf16_path;
+	__le16 *utf16_path = NULL;
 	__u8 oplock = SMB2_OPLOCK_LEVEL_NONE;
 	struct cifs_open_parms oparms;
 	struct cifs_fid fid;
+	bool use_cached_root_handle = false;
 
+	if ((strcmp(full_path, "") == 0) && (create_options == 0) &&
+	    (desired_access == FILE_READ_ATTRIBUTES) &&
+	    (create_disposition == FILE_OPEN) &&
+	    (tcon->nohandlecache == false)) {
+		rc = open_shroot(xid, tcon, &fid);
+		if (rc == 0)
+			use_cached_root_handle = true;
+	}
+
+	if (use_cached_root_handle == false) {
 		utf16_path = cifs_convert_path_to_utf16(full_path, cifs_sb);
 		if (!utf16_path)
 			return -ENOMEM;
@@ -65,6 +76,7 @@ smb2_open_op_close(const unsigned int xid, struct cifs_tcon *tcon,
 			kfree(utf16_path);
 			return rc;
 		}
+	}
 
 	switch (command) {
 	case SMB2_OP_DELETE:
@@ -107,6 +119,7 @@ smb2_open_op_close(const unsigned int xid, struct cifs_tcon *tcon,
 		break;
 	}
 
+	if (use_cached_root_handle == false)
 		rc = SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 	if (tmprc)
 		rc = tmprc;

fs/cifs/smb2ops.c

@@ -322,6 +322,40 @@ SMB3_request_interfaces(const unsigned int xid, struct cifs_tcon *tcon)
 }
 #endif /* STATS2 */
 
+/*
+ * Open the directory at the root of a share
+ */
+int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
+{
+	struct cifs_open_parms oparams;
+	int rc;
+	__le16 srch_path = 0; /* Null - since an open of top of share */
+	u8 oplock = SMB2_OPLOCK_LEVEL_NONE;
+
+	mutex_lock(&tcon->prfid_mutex);
+	if (tcon->valid_root_fid) {
+		cifs_dbg(FYI, "found a cached root file handle\n");
+		memcpy(pfid, tcon->prfid, sizeof(struct cifs_fid));
+		mutex_unlock(&tcon->prfid_mutex);
+		return 0;
+	}
+
+	oparams.tcon = tcon;
+	oparams.create_options = 0;
+	oparams.desired_access = FILE_READ_ATTRIBUTES;
+	oparams.disposition = FILE_OPEN;
+	oparams.fid = pfid;
+	oparams.reconnect = false;
+
+	rc = SMB2_open(xid, &oparams, &srch_path, &oplock, NULL, NULL);
+	if (rc == 0) {
+		memcpy(tcon->prfid, pfid, sizeof(struct cifs_fid));
+		tcon->valid_root_fid = true;
+	}
+	mutex_unlock(&tcon->prfid_mutex);
+	return rc;
+}
+
 static void
 smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 {
@@ -330,6 +364,7 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 	u8 oplock = SMB2_OPLOCK_LEVEL_NONE;
 	struct cifs_open_parms oparms;
 	struct cifs_fid fid;
+	bool no_cached_open = tcon->nohandlecache;
 
 	oparms.tcon = tcon;
 	oparms.desired_access = FILE_READ_ATTRIBUTES;
@@ -338,7 +373,11 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 	oparms.fid = &fid;
 	oparms.reconnect = false;
 
+	if (no_cached_open)
 		rc = SMB2_open(xid, &oparms, &srch_path, &oplock, NULL, NULL);
+	else
+		rc = open_shroot(xid, tcon, &fid);
+
 	if (rc)
 		return;
 
@@ -352,6 +391,7 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 			FS_DEVICE_INFORMATION);
 	SMB2_QFS_attr(xid, tcon, fid.persistent_fid, fid.volatile_fid,
 			FS_SECTOR_SIZE_INFORMATION); /* SMB3 specific */
+	if (no_cached_open)
 		SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 	return;
 }
@@ -394,6 +434,9 @@ smb2_is_path_accessible(const unsigned int xid, struct cifs_tcon *tcon,
 	struct cifs_open_parms oparms;
 	struct cifs_fid fid;
 
+	if ((*full_path == 0) && tcon->valid_root_fid)
+		return 0;
+
 	utf16_path = cifs_convert_path_to_utf16(full_path, cifs_sb);
 	if (!utf16_path)
 		return -ENOMEM;

fs/cifs/smb2proto.h

@@ -65,6 +65,8 @@ extern struct cifs_ses *smb2_find_smb_ses(struct TCP_Server_Info *server,
 extern int smb3_handle_read_data(struct TCP_Server_Info *server,
 				 struct mid_q_entry *mid);
 
+extern int open_shroot(unsigned int xid, struct cifs_tcon *tcon,
+			struct cifs_fid *pfid);
 extern void move_smb2_info_to_cifs(FILE_ALL_INFO *dst,
 				   struct smb2_file_all_info *src);
 extern int smb2_query_path_info(const unsigned int xid, struct cifs_tcon *tcon,