On Fri, 20 Mar 2009 18:41:40 -0700 (PDT) Roland McGrath rol...@redhat.com
wrote:
This adds the utrace facility, a new modular interface in the kernel for
implementing user thread tracing and debugging. This fits on top of the
tracehook_* layer, so the new code is well-isolated.
The new interface is in linux/utrace.h and the DocBook utrace book
describes it. It allows for multiple separate tracing engines to work in
parallel without interfering with each other. Higher-level tracing
facilities can be implemented as loadable kernel modules using this layer.
The new facility is made optional under CONFIG_UTRACE.
When this is not enabled, no new code is added.
It can only be enabled on machines that have all the
prerequisites and select CONFIG_HAVE_ARCH_TRACEHOOK.
In this initial version, utrace and ptrace do not play together at all.
If ptrace is attached to a thread, the attach calls in the utrace kernel
API return -EBUSY. If utrace is attached to a thread, the PTRACE_ATTACH
or PTRACE_TRACEME request will return EBUSY to userland. The old ptrace
code is otherwise unchanged and nothing using ptrace should be affected
by this patch as long as utrace is not used at the same time. In the
future we can clean up the ptrace implementation and rework it to use
the utrace API.
I'd be interested in seeing a bit of discussion regarding the overall value
of utrace - it has been quite a while since it floated past.
I assume that redoing ptrace to be a client of utrace _will_ happen, and
that this is merely a cleanup exercise with no new user-visible features?
The prototype utrace-ftrace interface seems to be more a cool toy rather
than a serious new kernel feature (yes?)
If so, what are the new killer utrace clients which would justify all these
changes?
Also, is it still the case that RH are shipping utrace? If so, for what
reasons and what benefits are users seeing from it?
And I recall that there were real problems wiring up the Feb 2007 version
of utrace to the ARM architecture. Have those issues been resolved? Are
any problems expected for any architectures?
Thanks.
