Re: supporting terminal ownership assignment (tcsetpgrp()) in posix_spawn

[Godmar Back <godmar@gmail.com>]

On Wed, Jun 9, 2021 at 8:00 AM Adhemerval Zanella <
adhemerval.zanella@linaro.org> wrote:

>
> The libc interface should be as generic possible to cover most users cases,
> I really don't want to add a posix_spawnattr_tcsetpgrp_np that uses the
> groupid implicit from POSIX_SPAWN_SETPGROUP to someone ask for a
> posix_spawnattr_tcsetpgrp_np_ex so one can set the groupid.
>
> Also, requiring POSIX_SPAWN_SETPGROUP for posix_spawnattr_tcsetpgrp_np is
> not really a good API, it adds subtle semantics (should it use a default
> value set by posix_spawnattr_init or should we fail with EINVAL), and adds
> complexity in the error path (we will need to either pre validate the
> posix_spawnattr_t input before start the process creation or handle a
> possible invalid combination on the helper process itself).
>
> That's why I am more inclined to follow the tcsetpgrp on the posix_spawn
> extension and let the caller set the required groups.
>
>
I just checked and I don't think this will even work.  The caller cannot
provide the process group id because the caller can't know it yet.
A typical sequence in the first child of a pipeline is "setpgid(0, 0);
tcsetpgrp(fd, getpgrp());" and AFAIK tcsetpgrp doesn't accept '0' to stand
for the
current process's process group.