On Wed, 2014-02-26 at 08:54 -0800, Chuck Lever wrote: > On Feb 26, 2014, at 8:25 AM, Simo Sorce <simo@xxxxxxxxxx> wrote: > > > On Wed, 2014-02-26 at 08:02 -0800, Chuck Lever wrote: > >> On Feb 26, 2014, at 6:39 AM, Simo Sorce <simo@xxxxxxxxxx> wrote: > >> > >>> On Wed, 2014-02-26 at 16:16 +1100, NeilBrown wrote: > >>>> See $SUBJ > >>>> > >>>> Shared libraries are usually versioned so you can release a new version with > >>>> an incompatible API and gradually transition to it. > >>>> > >>>> A rpc.mountd dlopens libnfsjunct.so with no version it is effectively > >>>> prohibited from ever changing the API in an incompatible way. > >>>> > >>>> Both Fedora and openSUSE get upset about packaging a libFOO.so in a non > >>>> "-devel" package and so trip over this library which clearly needs to be > >>>> installed even if you aren't doing 'devel'opment. > >>> > >>> Keep in mind this rule is there only for real shared libraries that are > >>> loaded by the the system loader. > >>> > >>> however it is waived for 'modules' that are opened dynamically but are > >>> private to the application. > >>> > >>>> I would like to change mountd as per the patch below to use the ".0" file. > >>>> I believe this will not break any installation as the ".so" is installed as a > >>>> symlink to the ".0" (or maybe ".0.0.0"). > >>>> > >>>> Would this be acceptable? > >>> > >>> It looks to me like this is an internal module for mountd that is not > >>> for use by other apps (which is why it is not versioned and can be > >>> changed at will as it is deployed at the same time mountd is ? > >> > >> The plug-in API is versioned internally, but maybe I got that wrong, > >> and should remove the API version field in favor of having consumers > >> load via a specific .so number. > > > > Either way works the same, it just changes what component makes the > > determination (app code vs linker) > > > >>> Or am I wrong here ? > >>> > >>> If I am not wrong I would be against this change personally and would > >>> rather move the .so file in a private library dir (if it is not already > >>> there) to make it clear it is a private module. > >> > >> rpc.mountd is the only user currently, but it’s not necessarily > >> private to mountd. A generic storage manager tool might use it to > >> resolve NFS and FedFS referrals for display, for example. We could > >> add plug-in API functions for creating and removing referrals to > >> enable generic tools to perform these operations. > > > > If it is a generic library why is it dlopened() instead of being simply > > linked in at build time ? > > Handling NFS and FedFS junctions requires support for sqlite3, LDAP, > and XML, among others. The maintainer of nfs-utils preferred to add > zero new build dependencies when we introduced this functionality. > The design we came up with was to dlopen() a library that would pull > in everything that was needed at run time. > > If the plug-in is not installed, mountd simply skips trying to resolve > junctions. This would be the case for embedded NFS servers, for > example. > Therefore this is an intimate library and the separation is a mere exercise in keeping the ability to not drag in dependencies in some install scenarios. > >> A separate directory makes sense if there’s more than one thing to put > >> in it. Right now we just have the plug-in library, and no plans to > >> add more. > > > > directories are cheap, don't fear them :) > > > >> I took an expedient approach when implementing the plug-in, and could > >> have gotten it wrong. I’m open to make this mechanism fit packaging > >> guidelines and requirements. > > > > Packaging guidelines vary depending on whether the library is public or > > private and therefore you need to guarantee ABI compatibility or not. > > > > I think you need to make that determination first. I think based on the above that we are looking at a library that is currently just a private plugin. The best course of action IMHO is to move it to /usr/lib[64]/nfs-mountd or something so that it is clear that it is a private plugin. At least until mountd is the only user. > I attempted to guarantee API compatibility using the API version field > and by publishing the API definition in a header under /usr/include. > By that definition it is a public API that happens to have only one > current user. API compatibility is all you need for a private plugin indeed, and perhaps not even that. However for a public library what would matter is ABI compatibility, not API compatibility. Given it is a lot of effort to guarantee a public API and that there really is no other user on the horizon I would recommend to consider this code a private plugin and treat it as such. That is: 1. consider it tightly integrated with rpc.mountd and to be installed in lockstep 2. consider it's API/ABI not stable and a private contract within rpc.mountd 3. package it accordingly Simo. -- Simo Sorce * Red Hat, Inc * New York -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
