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Finish ss example mapping connections to pids #151

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Finish ss example mapping connections to pids #151

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64 changes: 59 additions & 5 deletions examples/ss/ss.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ import (
"io/ioutil"
"log"
"os"
"strconv"
"strings"
"syscall"
"text/tabwriter"
Expand Down Expand Up @@ -86,17 +87,70 @@ func sockets() error {
}, "\t"))
defer w.Flush()

for _, diag := range msgs {
// XXX: A real implementation of ss would find the process holding
// inode of the socket. It would read /proc/<pid>/fd and find all sockets.
pidProgram := "not implemented"
inodeToPid := mapInodesToPid()

for _, diag := range msgs {
fmt.Fprintf(w, "%v\t%v\t%v\t%v:%v\t%v:%v\t%v\t%v\t%v\n",
linux.TCPState(diag.State), diag.RQueue, diag.WQueue,
diag.SrcIP().String(), diag.SrcPort(),
diag.DstIP().String(), diag.DstPort(),
diag.UID, diag.Inode, pidProgram)
diag.UID, diag.Inode, inodeToPid[diag.Inode])
}

return nil
}

func mapInodesToPid() (ret map[uint32]string) {
ret = map[uint32]string{}

fd, err := os.Open("/proc")
if err != nil {
fmt.Printf("Error opening /proc: %v", err)
}
defer fd.Close()

dirContents, err := fd.Readdirnames(0)
if err != nil {
fmt.Printf("Error reading files in /proc: %v", err)
}

for _, pid := range dirContents {
_, err := strconv.ParseUint(pid, 10, 32)
if err != nil {
// exclude files with a not numeric name. We only want to access pid directories
continue
}

pidDir, err := os.Open("/proc/" + string(pid) + "/fd/")
if err != nil {
// ignore errors:
// - missing directory, pid has already finished
// - permission denied
continue
}

fds, err := pidDir.Readdirnames(0)
if err != nil {
continue
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For errors like this, where there's no expectation that they might fail, we might want to actually fail, or at least comment if we expect them to fail for some reason.

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It could fail if the pid has finished and the dir does not exists any more.

Failing there will generate a lot of useless "warnings" IMHO

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In which case, can we at least add a comment to clarify?

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gomacro> import "os"
gomacro> a, err := os.Open("/proc/955374/fd")
gomacro> err
<nil>   // error
<--- here I kill process 955374
gomacro> a.Readdirnames(0)
[]      // []string
readdirent: no such file or directory   // error
gomacro>

It is commented in line 126

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Ah, I see. Considering that we can hit errors relating to non-existent PIDs in a few places, can we move that comment block in 126 out of that if block and move it somewhere, perhaps before the Open call just to make the comment a little more explicit?

}

for _, fd := range fds {
link, err := os.Readlink("/proc/" + string(pid) + "/fd/" + fd)
if err != nil {
continue
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Ditto here.

}

var inode uint32

_, err = fmt.Sscanf(link, "socket:[%d]", &inode)
if err != nil {
// this inode is not a socket
continue
}

ret[inode] = pid
}
}

return ret
}