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    SubjectRe: [PATCH 1/5] ftrace: use module notifier for function tracer
    * Anders Kaseorg (andersk@MIT.EDU) wrote:
    > On Wed, 22 Apr 2009, Masami Hiramatsu wrote:
    > > Could you also add "use text_poke() on x86" to your plan? :-)
    > That should be possible now that it is usable inside stop_machine(). It
    > would be nicer to have an API that isn’t x86-specific, though.
    > Another issue is that Ksplice supports patching rodata as well as text,
    > and text_poke() does not support changes bigger than PAGE_SIZE. Though
    > perhaps text_poke() is not the right function for rodata patches anyway.
    > > Hmm, I can't agree that we allow module to modify kernel text...
    > > Is that possible to separate kernel-text swapping routine from Ksplice
    > > module? In that case, we don't need to export text_mutex.
    > No, it’s not enough for Ksplice to lock the kernel text only while
    > actively swapping it. We also need to prevent changes to the kernel text
    > while Ksplice is doing run-pre matching to ensure safety. This means that
    > Ksplice wants to hold text_mutex for essentially the entire time it’s
    > running.

    how about a kernel Ksplice API which lets your patch modules get
    their handlers executed under the right execution context ? E.g. :

    int do_ksplice(void (*pre_hook)(struct blah *context),
    void (*code_update_hook)(struct blah *context),
    void (*post_hook)(struct blah *context));

    Which returns either 0 or -ESOMETHING. It would take care of locking and
    everything within core kernel code. The "patch" modules would simply
    provide the functions that does the code updates, assuming that the
    do_ksplice function makes sure to provide correct locking semantics.
    This way, the kernel code-base would contain the tricky locking bits.
    It seems much better than exporting the text_mutex to modules.


    > Anders

    Mathieu Desnoyers
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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