Add stripped-mount-point-paths argument

* accepts a regex pattern to be removed from the mountpoints
exported by the filesystem collector.
* addresses issue prometheus#66

README.md

@@ -99,3 +99,12 @@ docker pull prom/node-exporter
 
 docker run -d -p 9100:9100 --net="host" prom/node-exporter
 ```
+
+Note that Docker (and containers in general) is designed to separate a container's runtime from the
+host.  If you are running the node_exporter inside of Docker to export statistics about the host,
+use a command similar to:
+
+    docker run -d -p 9100:9100 -v "/proc:/host/proc" -v "/sys:/host/sys" -v "/:/rootfs" --net="host" prom/node-exporter -collector.procfs /host/proc -collector.sysfs /host/proc -collector.filesystem.ignored-mount-points "^/(sys|proc|dev|host|etc|rootfs/sys|rootfs/var/lib|)($|/)" -collector.filesystem.stripped-mount-point-paths "^/rootfs"
+
+See [Setting up the Node Exporter (in Docker)](https://www.digitalocean.com/community/tutorials/how-to-install-prometheus-using-docker-on-ubuntu-14-04#step-2-—-setting-up-node-exporter)
+for more details.

collector/filesystem_common.go

@@ -25,6 +25,7 @@ import (
 
 // Arch-dependent implementation must define:
 // * defIgnoredMountPoints
+// * defStrippedMountPointPaths
 // * filesystemLabelNames
 // * filesystemCollector.GetStats
 
@@ -34,11 +35,17 @@ var (
 		defIgnoredMountPoints,
 		"Regexp of mount points to ignore for filesystem collector.")
 
+	strippedMountPointPaths = flag.String(
+		"collector.filesystem.stripped-mount-point-paths",
+		defStrippedMountPointPaths,
+		"Regexp of mount point paths to remove for filesystem collector.")
+
 	filesystemLabelNames = []string{"device", "mountpoint", "fstype"}
 )
 
 type filesystemCollector struct {
-	ignoredMountPointsPattern *regexp.Regexp
+	ignoredMountPointsPattern      *regexp.Regexp
+	strippedMountPointPathsPattern *regexp.Regexp
 	sizeDesc, freeDesc, availDesc,
 	filesDesc, filesFreeDesc, roDesc *prometheus.Desc
 }
@@ -56,7 +63,8 @@ func init() {
 // Filesystems stats.
 func NewFilesystemCollector() (Collector, error) {
 	subsystem := "filesystem"
-	pattern := regexp.MustCompile(*ignoredMountPoints)
+	ignoredMountPointsPattern := regexp.MustCompile(*ignoredMountPoints)
+	strippedMountPointPathsPattern := regexp.MustCompile(*strippedMountPointPaths)
 
 	sizeDesc := prometheus.NewDesc(
 		prometheus.BuildFQName(Namespace, subsystem, "size"),
@@ -95,13 +103,14 @@ func NewFilesystemCollector() (Collector, error) {
 	)
 
 	return &filesystemCollector{
-		ignoredMountPointsPattern: pattern,
-		sizeDesc:                  sizeDesc,
-		freeDesc:                  freeDesc,
-		availDesc:                 availDesc,
-		filesDesc:                 filesDesc,
-		filesFreeDesc:             filesFreeDesc,
-		roDesc:                    roDesc,
+		ignoredMountPointsPattern:      ignoredMountPointsPattern,
+		strippedMountPointPathsPattern: strippedMountPointPathsPattern,
+		sizeDesc:                       sizeDesc,
+		freeDesc:                       freeDesc,
+		availDesc:                      availDesc,
+		filesDesc:                      filesDesc,
+		filesFreeDesc:                  filesFreeDesc,
+		roDesc:                         roDesc,
 	}, nil
 }
 

collector/filesystem_linux.go

@@ -18,15 +18,21 @@ package collector
 import (
 	"bufio"
 	"os"
+	"regexp"
 	"strings"
 	"syscall"
 
 	"github.com/prometheus/common/log"
 )
 
 const (
-	defIgnoredMountPoints = "^/(sys|proc|dev)($|/)"
-	ST_RDONLY             = 0x1
+	defIgnoredMountPoints      = "^/(sys|proc|dev)($|/)"
+	defStrippedMountPointPaths = ""
+	ST_RDONLY                  = 0x1
+)
+
+var (
+	rDoubleSlash = regexp.MustCompile("//")
 )
 
 type filesystemDetails struct {
@@ -60,7 +66,13 @@ func (c *filesystemCollector) GetStats() (stats []filesystemStats, err error) {
 			ro = 1
 		}
 
-		labelValues := []string{mpd.device, mpd.mountPoint, mpd.fsType}
+		mountPoint := rDoubleSlash.ReplaceAllString(
+			c.strippedMountPointPathsPattern.ReplaceAllString(mpd.mountPoint, "/"),
+			"/")
+		labelValues := []string{
+			mpd.device,
+			mountPoint,
+			mpd.fsType}
 		stats = append(stats, filesystemStats{
 			labelValues: labelValues,
 			size:        float64(buf.Blocks) * float64(buf.Bsize),