smb3: allow controlling length of time directory entries are cached with dir leases

Currently with directory leases we cache directory contents for a fixed period
of time (default 30 seconds) but for many workloads this is too short.  Allow
configuring the maximum amount of time directory entries are cached when a
directory lease is held on that directory. Add module load parm "max_dir_cache"

For example to set the timeout to 10 minutes you would do:

  echo 600 > /sys/module/cifs/parameters/dir_cache_timeout

or to disable caching directory contents:

  echo 0 > /sys/module/cifs/parameters/dir_cache_timeout
Reviewed-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/cached_dir.c

@@ -145,7 +145,7 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	const char *npath;
 
 	if (tcon == NULL || tcon->cfids == NULL || tcon->nohandlecache ||
-	    is_smb1_server(tcon->ses->server))
+	    is_smb1_server(tcon->ses->server) || (dir_cache_timeout == 0))
 		return -EOPNOTSUPP;
 
 	ses = tcon->ses;
@@ -582,7 +582,7 @@ cifs_cfids_laundromat_thread(void *p)
 			return 0;
 		spin_lock(&cfids->cfid_list_lock);
 		list_for_each_entry_safe(cfid, q, &cfids->entries, entry) {
-			if (time_after(jiffies, cfid->time + HZ * 30)) {
+			if (time_after(jiffies, cfid->time + HZ * dir_cache_timeout)) {
 				list_del(&cfid->entry);
 				list_add(&cfid->entry, &entry);
 				cfids->num_entries--;

fs/smb/client/cifsfs.c

@@ -117,6 +117,10 @@ module_param(cifs_max_pending, uint, 0444);
 MODULE_PARM_DESC(cifs_max_pending, "Simultaneous requests to server for "
 				   "CIFS/SMB1 dialect (N/A for SMB3) "
 				   "Default: 32767 Range: 2 to 32767.");
+unsigned int dir_cache_timeout = 30;
+module_param(dir_cache_timeout, uint, 0644);
+MODULE_PARM_DESC(dir_cache_timeout, "Number of seconds to cache directory contents for which we have a lease. Default: 30 "
+				 "Range: 1 to 65000 seconds, 0 to disable caching dir contents");
 #ifdef CONFIG_CIFS_STATS2
 unsigned int slow_rsp_threshold = 1;
 module_param(slow_rsp_threshold, uint, 0644);
@@ -1679,6 +1683,12 @@ init_cifs(void)
 			 CIFS_MAX_REQ);
 	}
 
+	/* Limit max to about 18 hours, and setting to zero disables directory entry caching */
+	if (dir_cache_timeout > 65000) {
+		dir_cache_timeout = 65000;
+		cifs_dbg(VFS, "dir_cache_timeout set to max of 65000 seconds\n");
+	}
+
 	cifsiod_wq = alloc_workqueue("cifsiod", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
 	if (!cifsiod_wq) {
 		rc = -ENOMEM;

fs/smb/client/cifsglob.h

@@ -2016,6 +2016,7 @@ extern unsigned int CIFSMaxBufSize;  /* max size not including hdr */
 extern unsigned int cifs_min_rcv;    /* min size of big ntwrk buf pool */
 extern unsigned int cifs_min_small;  /* min size of small buf pool */
 extern unsigned int cifs_max_pending; /* MAX requests at once to server*/
+extern unsigned int dir_cache_timeout; /* max time for directory lease caching of dir */
 extern bool disable_legacy_dialects;  /* forbid vers=1.0 and vers=2.0 mounts */
 extern atomic_t mid_count;