On Thu, Apr 29, 2021 at 04:31:41PM +0100, Richard W.M. Jones wrote: > On Thu, Apr 29, 2021 at 04:08:22PM +0100, Daniel P. Berrangé wrote: > > On Thu, Apr 29, 2021 at 04:00:38PM +0100, Richard W.M. Jones wrote: > > > On Thu, Apr 29, 2021 at 03:41:29PM +0100, Stefan Hajnoczi wrote: > > > > On Thu, Apr 29, 2021 at 03:22:59PM +0100, Richard W.M. Jones wrote: > > > > > On Thu, Apr 29, 2021 at 03:05:50PM +0100, Stefan Hajnoczi wrote: > > > > > > The purpose of this preview release is to discuss both the API > > > > > > design > > > > > > and general direction of the project. API documentation is available > > > > > > here: > > > > > > > > > > > > https://gitlab.com/libblkio/libblkio/-/blob/v0.1.0/docs/blkio.rst > > > > > > > > > > libvirt originally, and now libnbd, keep a per-thread error message > > > > > (stored in thread-local storage). It's a lot nicer than having to > > > > > pass &errmsg to every function. You can just write: > > > > > > > > > > if (nbd_connect_tcp (nbd, "remote", "nbd") == -1) { > > > > > fprintf (stderr, > > > > > "failed to connect to remote server: %s (errno = %d)\n", > > > > > nbd_get_error (), nbd_get_errno ()); > > > > > exit (EXIT_FAILURE); > > > > > } > > > > > > > > > > (https://libguestfs.org/libnbd.3.html#ERROR-HANDLING) > > > > > > > > > > It means you can extend the range of error information available in > > > > > future. Also you can return a 'const char *' and the application > > > > > doesn't have to worry about lifetimes, at least in the common case. > > > > > > > > Thanks for sharing the idea, I think it would work well for libblkio > > > > too. > > > > > > > > Do you ignore the dlclose(3) memory leak? > > > > > > I believe this mechanism in libnbd ensures there is no leak in the > > > ordinary shared library (not dlopen/dlclose) case: > > > > > > https://gitlab.com/nbdkit/libnbd/-/blob/f9257a9fdc68706a4079deb4ced61e1d468f28d6/lib/errors.c#L35 > > > > > > However I'm not sure what happens in the dlopen case, so I'm going to > > > test that out now ... > > > > pthread_key destructors are a disaster waiting to happen with > > dlclose, if the dlclose happens while non-main threads are > > still running. When those threads exit, they'll run the > > destructor which points to a function that is no longer > > resident in memory. > > > > IOW if you have destrutors, then you need to make sure your > > library uses "-z nodelete" when linking, to turn dlclose() > > into a no-op. > > I suspect letting the string leak is a better idea for libnbd.
Is dlclose() really that important ? libnbd is such a small thing that i doubt anyone will even notice the space being consumed if you mark it nodelete, and if an app is repeatedly doing an op that triggers dlopen+dlclose many times, then dlclose is especially useless. Personally I think removing memory leaks on thread exit is more important than honouring dlclose, as some apps can do pathelogical things creating *many* very short lived threads. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|