README: doc metrics details

Provide detailed information on exported smbmetrics counters, with
minimal 'howto'.

Signed-off-by: Shachar Sharon <ssharon@redhat.com>

README.md

@@ -6,8 +6,73 @@ Samba metrics exporter converts 'smbstatus' output into
 
 ## Build
 
-```bash
+```console
 $ make build
 
 $ make image-build
 ```
+
+
+## Query metrics
+
+When running (by privileged user) along-side active SMB server, `smbmetrics`
+exports a set of gauge metrics over HTTP via port `8080`. Most metrics become
+visible only when active SMB connections exists. Execute the folowing `curl`
+command on the same machine where you run `smbmetrics` instance:
+
+```console
+$ curl --request GET "http://localhost:8080/metrics"
+```
+
+## Exported metrics
+
+| Metric name               | Description                                      |
+|---------------------------|--------------------------------------------------|
+| `smb_metrics_status`      | Status and version of running process            |
+| `smb_sessions_total`      | Number of active SMB sessions                    |
+| `smb_tcon_total`          | Number of active SMB tree-connections            |
+| `smb_users_total`         | Number of connected users                        |
+| `smb_openfiles_total`     | Number of currently open files                   |
+| `smb_openfiles_access_rw` | Open files with `"RW"` access-mask set           |
+| `smb_share_activity`      | Number of remote machines using each share       |
+| `smb_share_byremote`      | Number of shares used by each remote machine     |
+
+
+
+## Example
+
+The following example is from a setup with 2 shares and 2 users connected and
+performing SMB file-system operations from 4 different machines:
+
+```console
+$ curl --request GET "http://localhost:8080/metrics"
+
+# HELP smb_metrics_status Current metrics-collector status versions
+# TYPE smb_metrics_status gauge
+smb_metrics_status{commitid="092fe2bb0",ctdbvers="4.20.0-103",sambaimage="",sambavers="4.20.0-103",version="v0.2-28-g092fe2b"} 1
+# HELP smb_sessions_total Number of currently active SMB sessions
+# TYPE smb_sessions_total gauge
+smb_sessions_total 8
+# HELP smb_tcon_total Number of currently active SMB tree-connections
+# TYPE smb_tcon_total gauge
+smb_tcon_total 8
+# HELP smb_users_total Number of currently active SMB users
+# TYPE smb_users_total gauge
+smb_users_total 2
+# HELP smb_openfiles_total Number of currently open files
+# TYPE smb_openfiles_total gauge
+smb_openfiles_total 5
+# HELP smb_openfiles_access_rw Number of open files with read-write access mode
+# TYPE smb_openfiles_access_rw gauge
+smb_openfiles_access_rw 4
+# HELP smb_share_activity Number of remote machines currently using a share
+# TYPE smb_share_activity gauge
+smb_share_activity{service="smbshare1"} 4
+smb_share_activity{service="smbshare2"} 2
+# HELP smb_share_for_remote Number of shares served for remote machine
+# TYPE smb_share_for_remote gauge
+smb_share_byremote{machine="192.168.122.71"} 2
+smb_share_byremote{machine="192.168.122.72"} 1
+smb_share_byremote{machine="192.168.122.73"} 2
+smb_share_byremote{machine="192.168.122.74"} 1
+```