prometheus: add btrfs_error_exporter example

examples/prometheus/btrfs_error_exporter

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+
+# Collect per-device btrfs filesystem errors.
+# Based on btrfs_stats.py (https://git.io/JkTIi) but rewritten to use
+# python-btrfs and not shell out multiple times to 'btrfs stats'.
+#
+# Written by Holger Hoffstätte <holger@applied-asynchrony.com>
+#
+# This file is part of python-btrfs.
+#
+# python-btrfs is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# python-btrfs is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with python-btrfs.  If not, see <http://www.gnu.org/licenses/>.
+
+import btrfs
+
+def get_btrfs_errors(mountpoint):
+    """Get per-device errors for a btrfs mount point.
+
+    Args:
+        mountpoint: (string) path to a mount point.
+
+    Yields:
+        (device, error_type, error_count, fsid) tuples, where:
+            device: (string) path to block device.
+            error_type: (string) type of btrfs error.
+            error_count: (int) number of btrfs errors of a given type.
+            fsid: (string) filesystem UUID.
+    """
+    fs = btrfs.FileSystem(mountpoint)
+    for dev in fs.devices():
+        devname = fs.dev_info(dev.devid).path.strip("/dev/")
+        error_counters = fs.dev_stats(dev.devid).counters
+        for error_name in error_counters.keys():
+            yield devname, error_name, error_counters[error_name], fs.fsid
+
+def btrfs_error_metrics():
+    """Collect btrfs error metrics.
+
+    Returns:
+        a list of strings to be exposed as Prometheus metrics or None.
+    """
+    metric = "node_btrfs_errors_total"
+    contents = [
+        "# TYPE %s counter" % metric,
+        "# HELP %s number of btrfs errors" % metric,
+    ]
+
+    for mountpoint in btrfs.utils.mounted_filesystem_paths():
+        for device, error_type, error_count, fsid in get_btrfs_errors(mountpoint):
+            contents.append('%s{device="%s",mountpoint="%s",type="%s",uuid="%s"} %d' %
+                (metric, device, mountpoint, error_type, fsid, error_count))
+
+    if len(contents) > 2:
+        # return metrics if there are actual btrfs filesystems found
+        # (i.e. `contents` contains more than just TYPE and HELP).
+        return contents
+
+if __name__ == "__main__":
+    contents = btrfs_error_metrics()
+    if contents is not None:
+        print("\n".join(contents))
+