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Re: license request for mgetgroups

From: James Youngman
Subject: Re: license request for mgetgroups
Date: Sun, 11 May 2014 08:47:36 +0100

The licence change is fine with me.

On 22 May 2013 23:25, "Pádraig Brady" <address@hidden> wrote:
On 05/22/2013 06:49 PM, Eric Blake wrote:
> I am trying to fix a bug in libvirt where a child process deadlocked
> because it called initgroups() in between fork and exec when the parent
> was multithreaded; it turns out that looking up group membership
> information requires a mutex, but if some other thread in the parent
> owns that mutex at the time of the fork, then the child will no longer
> have that thread around to ever release the mutex.  The solution is to
> not call initgroups, but to instead split the use of the underlying
> pieces of what initgroups does - a call to getgrouplist prior to forking
> (requires the mutex, but pre-fork is safe) and a call to setgroups after
> forking (no lookup required, therefore no mutex involved and no deadlock
> possible).  I ended up writing my own wrapper around getgrouplist, and
> only then discovered that gnulib's mgetgroups module does a better job
> at the task, except for one bit: mgetgroups is currently GPLv3 but
> libvirt wants LGPLv2+.
> Since getgrouplist is implemented in glibc as LGPLv2+, is there any
> objection to relicensing the following modules as LGPLv2+?
> For my argument on the xalloc-oversized module, observe that malloca.h
> (part of the LGPLv2+ malloca module) has effectively inlined the
> contents of lib/xalloc-oversized.h, so while the larger xalloc module
> will never be LGPL (it calls exit), the mere use of checking for
> oversized allocation has already been intentionally isolated for safe
> use in LGPL code.
> For my own contributions to these modules, I'm okay with relaxing to
> LGPLv2+.  I've cc'd all other contributors as tracked by gnulib.git's
> history (I'm not sure if coreutils.git would turn up any earlier authors
> from before we promoted mgetgroups from coreutils to gnulib).

I rewrote mgetgroups at one stage in coreutils.
I'm fine with the relicense.

James Youngman (CC'd) rewrote it to use getgrouplist if available:


> I did track the history of xalloc-oversized changes further back from when the
> macro was part of the larger xalloc.h (pre-split contributors marked in
> '()').  Module maintainers are denoted with *.
> getgroups [LGPLv3+] => *Jim, *Eric, Bruno, Paul
> getugroups [GPLv3+] => *Jim, Eric, Paul, Bruno, Lasse
> mgetgroups [GPLv3+] => *Jim, *Eric, Bruno
> xalloc-oversized [GPLv3+] => [*all] Eric, Paul, Jim, (Bruno)
> Also, I plan on submitting a doc patch on the gnulib initgroups.texi
> page warning about the portability pitfall of trying to use it to change
> the the id of a child process of a multithreaded parent.

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