[PATCH] LMDB full patch set

[Andrew Bartlett]

On Thu, 2018-05-03 at 20:07 +0100, Howard Chu wrote:
> Andrew Bartlett wrote:
> > On Thu, 2018-05-03 at 15:16 +0100, Howard Chu wrote:
> > > Andrew Bartlett wrote:
> > > > On Mon, 2018-04-16 at 16:57 +0100, Howard Chu wrote:
> > > > > mdb_env_close() will reset any reader slots owned by the process. The PID is
> > > > > stored in env->me_pid so unfortunately both parent and child will have the
> > > > > same PID recorded here after a fork. Thus env_close in the child would end up
> > > > > releasing the parent's reader slots. Fairly disastrous. Obviously we can fix
> > > > > this trivially by just using getpid() in env_close().
> > > > 
> > > > So, if after the fork(), we just ignore the old DB, except to close
> > > > mdb_env_get_fd() (which is not the lock file, and so has no fcntl
> > > > semantics) are we safe?
> > > 
> > > Safe, yes. But you could also just merge in this patch now
> > > http://www.openldap.org/devel/gitweb.cgi?p=openldap.git;a=tree;f=libraries/liblmdb;hb=3b01bbbc67389b63e6623da99d397283729e70e7
> > > 
> > > which makes mdb_env_close() safe, as mentioned above.
> > 
> > OK.  At this stage we were not planning on bundling lmdb into
> > third_party or vendoring it into Samba so we can't rely on recent
> > fixes, but once there is a released version with this in we can call
> > that within an #ifdef guard.  (bonus points if some CPP macro declares
> > it safe).
> 
> Next release probably in a couple weeks.
> 
> But not bundling makes no sense to me, you won't have MDB_VL32 support on 
> 32bit builds. As I recall, 32bit support was the main reason we started this 
> conversation however-many-years ago.

OK.  What happens if you build on 32 bit on the older versions?

In any case this is an AD DC only feature so far so I'm happy to
require that folks either have a modern lmdb or be on 64 bit.  It will
be different if the file server side takes it on, but folks running an
AD DC on a 32 bit old enterprise linux are rare I think. 

> > 
> > A reopen would still be nice because then we could match tdb where
> > would not need a new FD and so can't run out of FDs or have files go
> > missing under our feet.
> 
> OK, we can implement the mdb_env_postfork() API I described earlier.

Thanks,

Andrew Bartlett

-- 
Andrew Bartlett                       http://samba.org/~abartlet/
Authentication Developer, Samba Team  http://samba.org
Samba Developer, Catalyst IT          http://catalyst.net.nz/services/samba