process::Process:name is truncated for Linux

[svartalf]

/proc/{pid}/stat returns truncated (capped to 15 chars) process name, Process::cmdline could be used to fetch full process name if necessary.

Blocked by #97

[ChristianWitts]

/proc/{pid}/cmdline packs the entire command line executed into a single non-delimited string.
What could be done is following the symlink from /proc/{pid}/exe to the binary being executed ala this hackyness readlink -f /proc/{pid}/exe | rev | cut -d/ -f1 | rev but using nicer Rust stdlib (although having a check in the sys::unix::fs it looks to just use libcs stat for the so I'm not sure it is a solution out of the box).

[svartalf]

@ChristianWitts thank you for a note, it is a good option.

cmdline one has an important advantage, though, unprivileged processes can read it:

$ readlink exe
$ echo $?
1
$ cat cmdline
/usr/lib/polkit-kde-authentication-agent-1\0

Process::name could possibly try the readlink -f exe method and fall back to cmdline if the former method fails with the EACCES

[Lomanic]

gopsutil reads /proc/$PID/status to get numerous information for a process, including its name https://github.com/shirou/gopsutil/blob/e4ec7b275ada47ca32799106c2dba142d96aaf93/process/process_linux.go#L1006

This file is readable by everybody even for processes owned by root.

[svartalf]

@Lomanic brilliant idea! Reading only the first line from one file will be much cheaper comparing to "/stat" -> "readlink" -> "/cmdline" chain

[Lomanic]

In fact we fallback to reading /proc/$PID/cmdline if process name is longer or equals 15 chars in /proc/$PID/status (it's also capped in this file).

[svartalf]

@Lomanic, ah, okay, /proc/$PID/status is truncating the process name too, I misunderstood that part.
Well then, back to original idea :)

[ChristianWitts]

So I am actually an idiot, and did not notice the \0 null separator (because my cat did not reflect the \0 unlike less), so something like this would yield a Vector containing the executable, and all the arguments passed to it.

use std::{fs, path::Path};

fn cmd_args(filename: impl AsRef<Path>) -> String {
    let cmdline: String = fs::read_to_string(filename).expect("no such file")
        .parse().expect("Unable to parse file");
    cmdline
}

fn main() {
    let cmdline = cmd_args("/proc/$PID/cmdline");
    // Trim trailing NULL char before splitting into components
    let d: Vec<&str> = cmdline.trim_matches('\0').split('\0').collect();
    println!("{:?}", d);
}

[svartalf]

Yeah, cmdline parsing is implemented already, see it here and here, I just need to find time to address this issue.