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    SubjectRe: [take19 1/4] kevent: Core files.
    On Tuesday 17 October 2006 00:09, Johann Borck wrote:
    > Regarding mukevent I'm thinking of a event-type specific struct, that is
    > filled by the originating code, and placed into a per-event-type ring
    > buffer (which requires modification of kevent_wait).

    I'd personally worry about an implementation that used a per-event-type ring
    buffer, because you're still left having to hack around starvation issues in
    user-space. It is of course possible under the current model for anyone who
    wants per-event-type ring buffers to have them - just make separate kevent

    I haven't thought this through all the way yet, but why not have variable
    length event structures and have the kernel fill in a "next" pointer in each
    one? This could even be used to keep backwards binary compatibility while
    adding additional fields to the structures over time, though no space would
    be wasted on modern programs. You still end up with a question of what to do
    in case of overflow, but I'm thinking the thing to do in that case might be
    to start pushing overflow events onto a linked list which can be written back
    into the ring buffer when space becomes available. The appropriate behavior
    would be to throw new events on the linked list if the linked list had any
    events, so that things are delivered in order, but write to the mapped buffer
    directly otherwise.

    Deciding when to do that is tricky, and I haven't thought through the
    implications fully when I say this, but what about activating a bottom half
    when more space becomes available, and let that drain overflowed events back
    into the mapped buffer? Or perhaps the time to do it would be in the next
    blocking wait, when the queue emptied?

    I think it is very important to avoid any limits that can not be adjusted on
    the fly at run-time by CAP_SYS_ADMIN or what have you. Doing it this way may
    have other problems I've ignored but at least the big one - compile-time
    capacity limits in the year 2006 - would be largely avoided :P

    Nothing real solid yet, just some electrical storms in the grey matter...

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      Last update: 2006-10-17 08:03    [W:0.030 / U:5.380 seconds]
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