valgrind --track-fds, fuse and other issues

[Florian Weimer]

* Mark Wielaard:

> There was also a question about using valgrind on a program that
> implements a fuse file system, like the new glibc test support helper
> by Florian. I didn't give a very good answer to that one. Because I
> forgot that valgrind already should be able to handle that. Valgrind
> obviously already has to handle blocking syscalls that could be
> unblock by another thread. There is a "sim hint" to extend this to
> syscalls that might block when the underlying file system managed by
> the program itself.
>
>    --sim-hints=hint1,hint2,...
>        Pass miscellaneous hints to Valgrind which slightly modify the
>        simulated behaviour in nonstandard or dangerous ways, possibly to
>        help the simulation of strange features. By default no hints are
>        enabled. Use with caution! Currently known hints are:
>
> [...]
>
>        •   fuse-compatible: Enable special handling for certain system
>            calls that may block in a FUSE file-system. This may be
>            necessary when running Valgrind on a multi-threaded program
>            that uses one thread to manage a FUSE file-system and another
>            thread to access that file-system.
>
> Please let me know if this still doesn't work. This hint hasn't been
> updated in a long time and there might be some newer syscalls that
> should enable this hint, but don't (yet).

Very interesting!  It gets past a lot of things, but support for the
readlink system call appears to be missing.  Nevertheless, it already
found test bugs:

  support: Fix memory leaks in FUSE tests
  <https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=455c7622835d>

Thanks,
Florian