[Caml-list] Unix subdaemon, channels, filedescriptors....

[Basile STARYNKEVITCH <basile.starynkevitch@cea.fr>]

Dear All,

Sorry to coming back on channels and unix filedescriptors....

My problem:

I am coding in Ocaml a daemon program (the Poesia monitor - see
http://www.poesia-filter.org/) which happens to launch daemon
subprocesses, i.e. it fork and execs processes which do not use their
stdin stdout and stderr. Basically I would need something like a
Unix.process_none which forks a command without any stdin stdout and
stderr (which are technically redirected to /dev/null).

In practice I expect my poesia monitor to have lots (=hundreds) of
opened file descriptors, and I would like the child process to have no
file descriptor opened except stdin stdout stderr


I would like to close all the filedescriptors after the
fork. Unfortunately, the caml_out_channels_list primitive (coded in C
in ocaml/byterun/io.c), which is used in stdlib/pervasives.ml is not
published in pervasives.mli, and there is no caml_in_channels_list
primitive

May I suggest publishing this primitive in the future ocaml v3.05?

Also, Unix.open_process_in and related seems to forget closing the
file descriptors in the child process, as this example (running only
on Linux) demonstrates:

  #load "unix.cma";;
  (* opening bogus stuff *)
  let fooch = open_out "/tmp/foo" and barch = open_out "/tmp/bar" ;;

  (* demonstrating that the opened process has fooch and barch still opened *)
  let lsch = Unix.open_process_in "ls -l /proc/self/fd" in
  let rec loop () = 
      try 
          Printf.printf "%s\n" (input_line lsch); flush stdout;
	  loop ()
      with End_of_file -> ()
  in
  loop ();
  Unix.close_process_in lsch

When running this stuff, I am getting

total 0
lr-x------    1 basile   basile         64 Jul 17 15:57 0 -> pipe:[4700690]
l-wx------    1 basile   basile         64 Jul 17 15:57 1 -> pipe:[4700695]
l-wx------    1 basile   basile         64 Jul 17 15:57 2 -> pipe:[4700689]
l-wx------    1 basile   basile         64 Jul 17 15:57 3 -> /tmp/foo
l-wx------    1 basile   basile         64 Jul 17 15:57 4 -> /tmp/bar
lr-x------    1 basile   basile         64 Jul 17 15:57 5 -> /proc/18709/fd


I think that the child process (running the command) should not have
other opened filedescriptors than the documented stdin, stdout,
stderr, or that this behavior should be documented

How do I close (in Ocaml) every channel except stdin, stdout, stderr?

Regards.

-- 

N.B. Any opinions expressed here are only mine, and not of my organization.
N.B. Les opinions exprimees ici me sont personnelles et n engagent pas le CEA.

---------------------------------------------------------------------
Basile STARYNKEVITCH   ----  Commissariat à l Energie Atomique * France
DRT/LIST/DTSI/SLA * CEA/Saclay b.528 (p111f) * 91191 GIF/YVETTE CEDEX 
phone:+33 1,6908.6055; fax: 1,6908.8395 home: 1,4665.4553; mobile: 6,8501.2359
work email: Basile point Starynkevitch at cea point fr 
home email: Basile at Starynkevitch point net

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