On Wed, 26 Feb 2014 08:02:42 -0800 Chuck Lever <chuck.lever@xxxxxxxxxx> 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.
The problem I see with using the internal versioning is that if the version
is wrong, mountd fails to provide the required service.
So while I don't object to storing the version and performing the test, we
should design work-flows so that the test can only fail if there is a serious
configuration error, not just during a software upgrade.
>
> > 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.
This is the answer I was looking for to the question I asked earlier - thanks.
(So this is not an 'intimate library' to use Simo's term - it is truly a
shared library).
If, one day, an incompatible ABI change was needed then we could have an
rpc.mountd installed (or still running) which requires one ABI, and a
generic storage manager tool which requires the other.
So we really need them to be stored in two different files.
e.g. libnfsjunct.so.0 and libnfsjunct.so.1
To put it another way... libnfsjunct really is a shared library.
The *only* reason that rpc.mountd treats it differently to other shared
libraries is so that it can fail gracefully if the library isn't available
(thus removing hard dependencies) - a difference that I am very comfortable
with.
In every other way it should be treated like a shared library
- it should live in the standard /lib64 or whatever
- each application determines at compile-time what version it needs and finds
it by appending the version number to the base file name
- the "libfoo.so" file should live in the "-devel" package along with the
include file(s)
So rather than dlopening "libnfsjunct.so.0" rpc.mountd should probably
use a library name provided by the include file
Thanks,
NeilBrown
diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
index ca35de28847a..1a8c20492869 100644
--- a/utils/mountd/cache.c
+++ b/utils/mountd/cache.c
@@ -1139,7 +1139,11 @@ static struct exportent *lookup_junction(char *dom, const char *pathname,
struct link_map *map;
void *handle;
- handle = dlopen("libnfsjunct.so", RTLD_NOW);
+#ifdef JP_LIB_NAME
+ handle = dlopen(JP_LIB_NAME, RTLD_NOW);
+#else
+ handle = dlopen("libnfsjunct.so.0", RTLD_NOW);
+#endif
if (handle == NULL) {
xlog(D_GENERAL, "%s: dlopen: %s", __func__, dlerror());
return NULL;
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