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    Subject[RFC][PATCH 00/10] Task watchers v2 Introduction
    This is version 2 of my Task Watchers patches.

    Task watchers calls functions whenever a task forks, execs, changes its
    [re][ug]id, or exits.

    Task watchers is primarily useful to existing kernel code as a means making the
    code in fork and exit more readable. Kernel code uses these paths by marking a
    function as a task watcher much like modules mark their init functions with
    module_init(). This reduces the code length and complexity of copy_process().

    The first patch adds the basic infrastructure of task watchers: notification
    function calls in the various paths and a table of function pointers to be
    called. It uses an ELF section because parts of the table must be gathered
    from all over the kernel code and using the linker is easier than resolving
    and maintaining complex header interdependencies. An ELF table is also ideal
    because its read-only nature means that no locking nor list traversal are

    Subsequent patches adapt existing parts of the kernel to use a task watcher
    -- typically in the fork, clone, and exit paths:
    trace irqflags
    keys (for processes -- not for thread groups)
    process events connector

    I'm working on three more patches that add support for creating a task watcher
    from within a module using an ELF section. I've not posted that work because it
    hasn't successfully booted much less completed the small selection of smoke
    tests I ran on these.

    Mark the task watcher table ELF section read-only. I've googled, read
    man pages, navigated the info pages, tried using PHDR, and according to
    the output of objdump, had no success. I'd really appreciate a pointer
    to an example showing what makes ld mark a kernel ELF section read-only.

    Dropped use of notifier chains
    Dropped per-task watchers
    Can be implemented on top of this
    Still requires notifier chains
    Dropped taskstats conversion
    Parts of taskstats had to move away from the regions of
    copy_process() and do_exit() where task_watchers are notified
    Used linker script mechanism suggested by Al Viro
    Created one "list" of watchers per event as requested by Andrew Morton
    No need to multiplex a single function call
    Easier to static register/unregister watchers: 1 line of code
    val param now used for:
    WATCH_TASK_INIT: clone_flags
    WATCH_TASK_CLONE: clone_flags
    WATCH_TASK_EXIT: exit code
    WATCH_TASK_*: <unused>
    Renamed notify_watchers() to notify_task_watchers()
    Replaced: if (err != 0) --> if (err)
    Added patches converting more "features" to use task watchers
    Added return code handling to WATCH_TASK_INIT
    Return code handling elsewhere didn't seem appropriate
    since there was generally no response necessary
    Fixed process keys free to handle failure in fork as originally coded
    in copy_process
    Added process keys code to watch for [er][ug]id changes

    Added ability to cause fork to fail with NOTIFY_STOP_MASK
    Added WARN_ON() when watchers cause WATCH_TASK_FREE to stop early
    Moved fork invocation
    Moved exec invocation
    Added current as argument to exec invocation
    Moved exit code assignment
    Added id change invocations
    Based on Jes Sorensen's Task Notifiers patches

    -Matt Helsley
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      Last update: 2006-09-29 04:15    [W:0.023 / U:9.332 seconds]
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