Messages in this thread | | | Date | Mon, 23 Mar 2009 10:57:11 +0000 | Subject | Re: [PATCH 2/3] utrace core | From | Will Newton <> |
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On Sat, Mar 21, 2009 at 8:49 AM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Fri, 20 Mar 2009 18:41:40 -0700 (PDT) Roland McGrath <roland@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?
It looks like utrace could provide a nice way to do low latency tracing of userspace processes via a hardware interface (e.g. JTAG or custom trace hardware). The only way to do that at present is to scatter bits of instrumentation throughout the kernel.
I would like to see utrace merged so I can work on that type of feature. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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