[dm-devel] [PATCH 2/3] libmutipath: don't close fd on dm_lib_release

[Martin Wilck]

On Wed, 2020-03-25 at 17:00 -0500, Benjamin Marzinski wrote:
> On Wed, Mar 25, 2020 at 03:52:55PM -0500, Benjamin Marzinski wrote:
> > On Wed, Mar 25, 2020 at 03:16:50PM +0000, Martin Wilck wrote:
> > > On Tue, 2020-03-24 at 16:03 -0500, Benjamin Marzinski wrote:
> > > 
> > > AFAICS, this function has been in libdm since 1.02.111. We
> > > support
> > > 1.02.89 (if all features enabled, otherwise even older). Perhaps
> > > we
> > > should make this function call conditional on the libdm verson?
> > > 
> > > But perhaps more importantly, why do we still need to call
> > > dm_lib_release()? AFAICS it's only needed for systems that have
> > > no udev
> > > support for creating device nodes (to call update_devs() via
> > > dm_lib_release()), and we don't support that anymore anyway, do
> > > we? 
> > > 
> > > Since 26c4bb0, we're always setting the
> > > DM_UDEV_DISABLE_LIBRARY_FALLBACK flag, and the cookie, too
> > > (we aren't setting it for DM_DEVICE_RELOAD, but it isn't needed
> > > for
> > > that, either, since no device nodes need to be created or
> > > removed); so
> > > dm_lib_release() should really have no effect.
> > > 
> > > Regards
> > > Martin
> > 
> > Good call. I'll redo this patch.
> 
> Actually, I've changed my mind. Calling dm_lib_release() lets us
> release
> the memory that device-mapper uses to store all the node ops that it
> was saving up.  Without calling dm_lib_release(), AFAICS, that memory
> keeps growing until the daemon exits.

Sorry for coming back to this so late. I've just stared at the libdm
code again. 

We always set DM_UDEV_DISABLE_LIBRARY_FALLBACK. In the standard CREATE
and REMOVE cases, libdm doesn't stack any operations if this flag is
set. The only exceptions are 

 a) RESUME operations with DM_ADD_NODE_ON_RESUME set. This happens
implicity when we create new maps
 b) RENAME operations

In both cases, we call dm_udev_wait() after the libdm operation, which
calls update_devs() and should thus have the same effect as
dm_lib_release(). IOW, I still believe we don't need to call
dm_lib_release() any more.

Regards,
Martin

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE  Software Solutions Germany GmbH
HRB 36809, AG Nürnberg GF: Felix
Imendörffer