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. > >> 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 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. -- Chuck Lever chuck[dot]lever[at]oracle[dot]com -- 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
