Identify UST threads by changing thread names

Hi,

This is an RFC patch for comments and ideas about how this should be done. In recent work I've been doing, I found out that some UST- instrumented userspace process was preempting itself. Looking further, it was not the same TID, but the same process name. These processes were LTTng-UST listener threads, but were not identified as so. Adding a simple symbol, such as "-ust" or "-lttng" at the end of the process name would help to identify such process directly in the generated trace.

You'll find below two different implementations with their pros and cons, for which the "-ust" symbol was choosen:

1/ An implementation using prctl
It works properly on Linux, but I didn't find a way to make it work under FreeBSD, hence the empty function in FreeBSD case (keeping the situation as it is now).

Raphaël Beamonte (1):
Add -ust to the name of UST threads of the application

 liblttng-ust/compat.h         | 22 ++++++++++++++++++++++
 liblttng-ust/lttng-ust-comm.c |  2 ++
 2 files changed, 24 insertions(+)

2/ An implementation using pthread
It works on both Linux and FreeBSD, but requires to add a link to the pthread library in liblttng-ust Makefile.am. Also, this approach relies on the presence of the pthread_setname_np function, which was included in glibc 2.12, meaning it will not work with older versions (but this should not be a problem?)

Raphaël Beamonte (1):
Add -ust to the name of UST threads of the application

 liblttng-ust/Makefile.am      |  1 +
 liblttng-ust/compat.h         | 35 +++++++++++++++++++++++++++++++++++
 liblttng-ust/lttng-ust-comm.c |  2 ++
 3 files changed, 38 insertions(+)

I'll wait for your comments and ideas on that subject.

Thanks,
Raphaël