podman-top: use containers/psgo

Use github.com/containers/psgo instead of execing `ps (1)`.  The psgo
library enables a much more flexible interface with respect to which
data to be printed (e.g., capabilities, seccomp mode, PID, PCPU, etc.)
while the output can be parsed reliably.  The library does not use
ps (1) but parses /proc and /dev instead.  To list the processes of a
given container, psgo will join the mount namespace of the given
container and extract all data from there.

Notice that this commit breaks compatibility with docker-top.

Signed-off-by: Valentin Rothberg <vrothberg@suse.com>

Closes: #1113
Approved by: rhatdan

1 files changed, 24 insertions, 7 deletions

diff --git a/cmd/podman/top.go b/cmd/podman/top.go
index d848723e2..749d97505 100644
--- a/cmd/podman/top.go
+++ b/cmd/podman/top.go
@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"strings"
 	"text/tabwriter"
 
 	"github.com/pkg/errors"
@@ -14,11 +15,15 @@ import (
 var (
 	topFlags = []cli.Flag{
 		LatestFlag,
+		cli.BoolFlag{
+			Name:   "list-descriptors",
+			Hidden: true,
+		},
 	}
-	topDescription = `
-   podman top
-
-	Display the running processes of the container.
+	topDescription = `Display the running processes of the container.  Specify format descriptors
+to alter the output.  You may run "podman top -l pid pcpu seccomp" to print
+the process ID, the CPU percentage and the seccomp mode of each process of
+the latest container.
 `
 
 	topCommand = cli.Command{
@@ -27,7 +32,7 @@ var (
 		Description:    topDescription,
 		Flags:          topFlags,
 		Action:         topCmd,
-		ArgsUsage:      "CONTAINER-NAME",
+		ArgsUsage:      "CONTAINER-NAME [format descriptors]",
 		SkipArgReorder: true,
 	}
 )
@@ -37,6 +42,15 @@ func topCmd(c *cli.Context) error {
 	var err error
 	args := c.Args()
 
+	if c.Bool("list-descriptors") {
+		descriptors, err := libpod.GetContainerPidInformationDescriptors()
+		if err != nil {
+			return err
+		}
+		fmt.Println(strings.Join(descriptors, "\n"))
+		return nil
+	}
+
 	if len(args) < 1 && !c.Bool("latest") {
 		return errors.Errorf("you must provide the name or id of a running container")
 	}
@@ -50,9 +64,12 @@ func topCmd(c *cli.Context) error {
 	}
 	defer runtime.Shutdown(false)
 
+	var descriptors []string
 	if c.Bool("latest") {
+		descriptors = args
 		container, err = runtime.GetLatestContainer()
 	} else {
+		descriptors = args[1:]
 		container, err = runtime.LookupContainer(args[0])
 	}
 
@@ -67,12 +84,12 @@ func topCmd(c *cli.Context) error {
 		return errors.Errorf("top can only be used on running containers")
 	}
 
-	psOutput, err := container.GetContainerPidInformation([]string{})
+	psOutput, err := container.GetContainerPidInformation(descriptors)
 	if err != nil {
 		return err
 	}
 
-	w := tabwriter.NewWriter(os.Stdout, 20, 1, 3, ' ', 0)
+	w := tabwriter.NewWriter(os.Stdout, 5, 1, 3, ' ', 0)
 	for _, proc := range psOutput {
 		fmt.Fprintln(w, proc)
 	}