[fuse-devel] how to detect if within Fuse thread / calling fuse_interrupted() from non-Fuse thread

[Michael B. <mic...@go...>]

Hi all,

We recently switched the interruption support in our Fuse client from
the signal handler approach (via -o intr_signal) to calling
fuse_interrupted(). In practice, it was not feasible to deal with
signal handlers in a multi-threaded environment. We even ended up
implementing an own high-level, signal-safe thread-local storage. But
in the end, we abandoned everything for the much simpler
fuse_interrupted() approach.

Now fuse_interrupted() is called as part of our retry logic to see if
a retry should be aborted. This retry logic and consequently
fuse_interrupted() gets also called from non-Fuse threads e.g., our
own threads which do periodic tasks. This resulted in segmentation
faults since "fuse_req_interrupted()", called by fuse_interrupted()
[1], does not check if the passed pointer is NULL. Would you mind
adding a NULL check in fuse_req_interrupted()?

As a work around, we check if fuse_get_context()->fuse is not NULL
before calling fuse_interrupted(). But this approach also fails on
older Fuse versions (e.g., Fuse 2.8.3 shipped with CentOS 6) since
previous versions do not zero the struct fuse_context_i (older
versions call "malloc" at this point [2]).

Of course, a possible solution is to make sure that our code never
calls fuse_interrupted() in our own threads. However, I was wondering
if the current Fuse API provides any better trick than the stated one
above to find out if one is inside a Fuse thread or not.

Best regards,
Michael Berlin

[1] http://fuse.git.sourceforge.net/git/gitweb.cgi?p=fuse/fuse;a=blob;f=lib/fuse.c;h=644878b9425a85e57f1e9296256ecba1259d150a;hb=HEAD#l4297
[2] http://fuse.git.sourceforge.net/git/gitweb.cgi?p=fuse/fuse;a=blob;f=lib/fuse.c;h=644878b9425a85e57f1e9296256ecba1259d150a;hb=HEAD#l2447