smb3: show beginning time for per share stats

In analyzing problems, one missing piece of debug data is when the
mount occurred.  A related problem is when collecting stats we don't
know the  period of time the stats covered, ie when this set of stats
for the tcon started to be collected.  To make debugging easier track
the stats begin time. Set it when the mount occurred at mount time,
and reset it to current time whenever stats are reset. For example,

...
1) \\localhost\test
SMBs: 14 since 2024-01-17 22:17:30 UTC
Bytes read: 0  Bytes written: 0
Open files: 0 total (local), 0 open on server
TreeConnects: 1 total 0 failed
TreeDisconnects: 0 total 0 failed
...
2) \\localhost\scratch
SMBs: 24 since 2024-01-17 22:16:04 UTC
Bytes read: 0  Bytes written: 0
Open files: 0 total (local), 0 open on server
TreeConnects: 1 total 0 failed
TreeDisconnects: 0 total 0 failed
...

Note the time "since ... UTC" is now displayed in /proc/fs/cifs/Stats
for each share that is mounted.
Suggested-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/cifs_debug.c

@@ -659,6 +659,7 @@ static ssize_t cifs_stats_proc_write(struct file *file,
 					spin_lock(&tcon->stat_lock);
 					tcon->bytes_read = 0;
 					tcon->bytes_written = 0;
+					tcon->stats_from_time = ktime_get_real_seconds();
 					spin_unlock(&tcon->stat_lock);
 					if (server->ops->clear_stats)
 						server->ops->clear_stats(tcon);
@@ -737,8 +738,9 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 				seq_printf(m, "\n%d) %s", i, tcon->tree_name);
 				if (tcon->need_reconnect)
 					seq_puts(m, "\tDISCONNECTED ");
-				seq_printf(m, "\nSMBs: %d",
-					   atomic_read(&tcon->num_smbs_sent));
+				seq_printf(m, "\nSMBs: %d since %ptTs UTC",
+					   atomic_read(&tcon->num_smbs_sent),
+					   &tcon->stats_from_time);
 				if (server->ops->print_stats)
 					server->ops->print_stats(m, tcon);
 			}

fs/smb/client/cifsglob.h

@@ -1207,6 +1207,7 @@ struct cifs_tcon {
 	__u64    bytes_read;
 	__u64    bytes_written;
 	spinlock_t stat_lock;  /* protects the two fields above */
+	time64_t stats_from_time;
 	FILE_SYSTEM_DEVICE_INFO fsDevInfo;
 	FILE_SYSTEM_ATTRIBUTE_INFO fsAttrInfo; /* ok if fs name truncated */
 	FILE_SYSTEM_UNIX_INFO fsUnixInfo;

fs/smb/client/misc.c

@@ -140,6 +140,7 @@ tcon_info_alloc(bool dir_leases_enabled)
 	spin_lock_init(&ret_buf->stat_lock);
 	atomic_set(&ret_buf->num_local_opens, 0);
 	atomic_set(&ret_buf->num_remote_opens, 0);
+	ret_buf->stats_from_time = ktime_get_real_seconds();
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	INIT_LIST_HEAD(&ret_buf->dfs_ses_list);
 #endif