[PATCH] runfvp: Ensure new process group is in the foreground

[PATCH] runfvp: Ensure new process group is in the foreground

[Ross Burton]

From: Peter Hoyes <Peter.Hoyes@arm.com>

When a new process group is created, it is launched in the background
and any attempt to access the session terminal triggers a SIGTTIN (for
stdin) or SIGTTOU (for stdout) signal. These are ignored in an
interactive shell, but the default signal behavior in a new job is to
send a SIGTSTP to the whole process group. This causes runfvp to hang
when executed via a subprocess when stdin is accessed.

After creating a new process group, use tcsetpgrp to make the new group
the foreground process for the terminal associated with stdin/stdout.

The documentation for tcsetgrp states that tcsetpgrp itself raises a
SIGTTOU signal, so set this signal to SIG_IGN.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: I349a825df7fcb8a3cedb81762b901c6f50fa53b5
---
 scripts/runfvp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/runfvp b/scripts/runfvp
index 97836726..9188a3a6 100755
--- a/scripts/runfvp
+++ b/scripts/runfvp
@@ -4,6 +4,7 @@ import asyncio
 import json
 import os
 import re
+import signal
 import sys
 import subprocess
 import pathlib
@@ -220,6 +221,9 @@ if __name__ == "__main__":
         # Set the process group so that it's possible to kill runfvp and
         # everything it spawns easily.
         os.setpgid(0, 0)
+        signal.signal(signal.SIGTTOU, signal.SIG_IGN)
+        os.tcsetpgrp(sys.stdin.fileno(), os.getpgrp())
         runfvp(sys.argv[1:])
+
     except KeyboardInterrupt:
         pass
-- 
2.25.1

Re: [meta-arm] [PATCH] runfvp: Ensure new process group is in the foreground

[Ross Burton]

Breaks in CI, v2 incoming shortly.

Ross

On Wed, 20 Oct 2021 at 18:22, Ross Burton via lists.yoctoproject.org
<ross=burtonini.com@lists.yoctoproject.org> wrote:
>
> From: Peter Hoyes <Peter.Hoyes@arm.com>
>
> When a new process group is created, it is launched in the background
> and any attempt to access the session terminal triggers a SIGTTIN (for
> stdin) or SIGTTOU (for stdout) signal. These are ignored in an
> interactive shell, but the default signal behavior in a new job is to
> send a SIGTSTP to the whole process group. This causes runfvp to hang
> when executed via a subprocess when stdin is accessed.
>
> After creating a new process group, use tcsetpgrp to make the new group
> the foreground process for the terminal associated with stdin/stdout.
>
> The documentation for tcsetgrp states that tcsetpgrp itself raises a
> SIGTTOU signal, so set this signal to SIG_IGN.
>
> Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
> Change-Id: I349a825df7fcb8a3cedb81762b901c6f50fa53b5
> ---
>  scripts/runfvp | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/scripts/runfvp b/scripts/runfvp
> index 97836726..9188a3a6 100755
> --- a/scripts/runfvp
> +++ b/scripts/runfvp
> @@ -4,6 +4,7 @@ import asyncio
>  import json
>  import os
>  import re
> +import signal
>  import sys
>  import subprocess
>  import pathlib
> @@ -220,6 +221,9 @@ if __name__ == "__main__":
>          # Set the process group so that it's possible to kill runfvp and
>          # everything it spawns easily.
>          os.setpgid(0, 0)
> +        signal.signal(signal.SIGTTOU, signal.SIG_IGN)
> +        os.tcsetpgrp(sys.stdin.fileno(), os.getpgrp())
>          runfvp(sys.argv[1:])
> +
>      except KeyboardInterrupt:
>          pass
> --
> 2.25.1
>
>
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