Add cwd template variable

Author: alexandreh2ag

README.md

@@ -111,6 +111,7 @@ Template variables available:
 - `{{.Cgroups}}` contains (if supported) the cgroups of the process
   (`/proc/self/cgroup`). This is particularly useful for identifying to which container
   a process belongs.
+- `{{.Cwd}}` contains the current working directory of the process (`/proc/self/cwd`).
 
 Using `PID` or `StartTime` is discouraged: this is almost never what you want,
 and is likely to result in high cardinality metrics which Prometheus will have

common.go

@@ -11,6 +11,7 @@ type (
 		Cmdline   []string
 		Cgroups   []string
 		Username  string
+		Cwd       string
 		PID       int
 		StartTime time.Time
 	}

config/config.go

@@ -55,6 +55,7 @@ type (
 		ExeBase   string
 		ExeFull   string
 		Username  string
+		Cwd       string
 		PID       int
 		StartTime time.Time
 		Matches   map[string]string
@@ -124,6 +125,7 @@ func (m *matchNamer) MatchAndName(nacl common.ProcAttributes) (bool, string) {
 		Username:  nacl.Username,
 		PID:       nacl.PID,
 		StartTime: nacl.StartTime,
+		Cwd:       nacl.Cwd,
 	})
 	return true, buf.String()
 }

config/config_test.go

@@ -64,10 +64,13 @@ process_names:
   - comm:
     - cat
     name: "{{.StartTime}}"
+  - comm:
+    - echo
+    name: "{{.Cwd}}"
 `
 	cfg, err := GetConfig(yml, false)
 	c.Assert(err, IsNil)
-	c.Check(cfg.MatchNamers.matchers, HasLen, 3)
+	c.Check(cfg.MatchNamers.matchers, HasLen, 4)
 
 	postgres := common.ProcAttributes{Name: "postmaster", Cmdline: []string{"/usr/bin/postmaster", "-D", "/data/pg"}}
 	found, name := cfg.MatchNamers.matchers[0].MatchAndName(postgres)
@@ -92,4 +95,13 @@ process_names:
 	found, name = cfg.MatchNamers.matchers[2].MatchAndName(cat)
 	c.Check(found, Equals, true)
 	c.Check(name, Equals, now.String())
+
+	echo := common.ProcAttributes{
+		Name:    "echo",
+		Cmdline: []string{"/bin/echo"},
+		Cwd:     "/",
+	}
+	found, name = cfg.MatchNamers.matchers[3].MatchAndName(echo)
+	c.Check(found, Equals, true)
+	c.Check(name, Equals, "/")
 }

proc/base_test.go

@@ -67,7 +67,7 @@ func (n namer) MatchAndName(nacl common.ProcAttributes) (bool, string) {
 
 func newProcIDStatic(pid, ppid int, startTime uint64, name string, cmdline []string) (ID, Static) {
 	return ID{pid, startTime},
-		Static{name, cmdline, []string{}, ppid, time.Unix(int64(startTime), 0).UTC(), 1000}
+		Static{name, cmdline, []string{}, "/", ppid, time.Unix(int64(startTime), 0).UTC(), 1000}
 }
 
 func newProc(pid int, name string, m Metrics) IDInfo {

proc/read.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/prometheus/procfs"
@@ -31,6 +32,7 @@ type (
 		Name         string
 		Cmdline      []string
 		Cgroups      []string
+		Cwd          string
 		ParentPid    int
 		StartTime    time.Time
 		EffectiveUID int
@@ -137,6 +139,7 @@ type (
 		status  *procfs.ProcStatus
 		cmdline []string
 		cgroups []procfs.Cgroup
+		cwd     string
 		io      *procfs.ProcIO
 		fs      *FS
 		wchan   *string
@@ -313,6 +316,21 @@ func (p *proccache) getCgroups() ([]procfs.Cgroup, error) {
 	return p.cgroups, nil
 }
 
+func (p *proccache) getCwd() (string, error) {
+	if p.cwd == "" {
+		cwd, err := p.Cwd()
+
+		if err != nil && strings.Contains(err.Error(), "permission denied") {
+			cwd = "-"
+		} else if err != nil {
+			return "", err
+		}
+		p.cwd = cwd
+	}
+
+	return p.cwd, nil
+}
+
 // GetProcID implements Proc.
 func (p *proccache) GetProcID() (ID, error) {
 	if p.procid == nil {
@@ -394,10 +412,17 @@ func (p *proccache) GetStatic() (Static, error) {
 		}
 	}
 
+	// /proc/<pid>/cwd is normally world-readable.
+	cwd, err := p.getCwd()
+	if err != nil {
+		return Static{}, err
+	}
+
 	return Static{
 		Name:         stat.Comm,
 		Cmdline:      cmdline,
 		Cgroups:      cgroupsStr,
+		Cwd:          cwd,
 		ParentPid:    stat.PPID,
 		StartTime:    startTime,
 		EffectiveUID: int(status.UIDs[1]),

proc/read_test.go

@@ -64,6 +64,7 @@ func TestReadFixture(t *testing.T) {
 		Name:         "process-exporte",
 		Cmdline:      []string{"./process-exporter", "-procnames", "bash"},
 		Cgroups:      []string{"/system.slice/docker-8dde0b0d6e919baef8d635cd9399b22639ed1e400eaec1b1cb94ff3b216cf3c3.scope"},
+		Cwd:          "/tmp",
 		ParentPid:    10884,
 		StartTime:    stime,
 		EffectiveUID: 1000,

proc/tracker.go

@@ -432,6 +432,7 @@ func (t *Tracker) Update(iter Iter) (CollectErrors, []Update, error) {
 			Cmdline:   idinfo.Cmdline,
 			Cgroups:   idinfo.Cgroups,
 			Username:  t.lookupUid(idinfo.EffectiveUID),
+			Cwd:       idinfo.Cwd,
 			PID:       idinfo.Pid,
 			StartTime: idinfo.StartTime,
 		}