Re: setting working dir in posix_spawn() (Re: Fix 'git log' early pager startup error case)

From: Joshua Juran <jjuran@gmail.com>
Date: Aug 26, 2010, 07:16 UTC
Message-ID: <65AAB642-0AEB-40F3-8C33-81AA2C110D3E@gmail.com>
In-Reply-To: <20100826061815.GH9708@burratino>

On Aug 25, 2010, at 11:18 PM, Jonathan Nieder wrote:

Show 16 quoted lines

> Eric Blake wrote:
>> On 08/25/2010 01:00 AM, Johannes Sixt wrote:
>
>>> Just FYI, posix_spawn() is not sufficiently capable for the  
>>> demands of
>>> start_command(): It doesn't allow to set a new CWD for the spawned  
>>> process.
>>
>> And even if posix_spawn() were capable, cygwin doesn't yet  
>> implement it.
>
> Hmm, okay.  You have access to win32api, though, right?  So it should
> be possible to reuse code from compat/mingw.c::mingw_spawnvpe.
>
> Do you think there would be any interest in a posix_spawn() variant
> that takes a dir parameter?

Another option would be a variant of vfork() where munging file descriptors, cwd, etc. prior to exec is well defined. In Lamp (Lamp ain't Mac POSIX), vfork() does this already; in Linux you'd just use fork(). The problem is that currently no common interface exists which guarantees behavior which is both sufficient and cheap -- vfork() promises nothing at all, and fork() is expensive (if available at all) on some platforms, guaranteeing much more than is often needed.

It would be useful to have something in between vfork() and fork(), though I'm not sure what it should be called.

Josh