[PATCH][RFC] Signal-per-fd for RT signals

[Vitaly Luban <vitaly@luban.org>]

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Hi,

I'm sorry, the previous message slipped out w/o subj.

Attached patch is an implementation of "signal-per-fd"
enhancement to kernel RT signal mechanism, AFAIK first
proposed by A. Chandra and D. Mosberger :

http://www.hpl.hp.com/techreports/2000/HPL-2000-174.html

which should dramatically increase linux based network
servers scalability.

Patch is made against 2.4.4 tree.

This patch allows to set signal-per-fd mode per each
file descriptor by introducing new fcntls "F_SETAUXFL"
and "F_GETAUXFL" with one possible argument "O_ONESIGFD"
to F_SETAUXFL defined.

When set, no additional siginfo will be queued for an
RT signal, generated by event on file descriptor, while
there is already one queued, though event report field
in already queued struct siginfo - "si_band" is updated.

I'd also like to hear an opinion on the signal filtering
capability. I.e, it's relatively easy to filter signals
upon an interest mask, supplied by the same F_SETAUXFL in
the form of POLL_... This will bring functionality of RT
signals event notification on the level with 'select' or
'poll' one, while more efficient and scalable. If there's
an interest in such a feature, I'd be eager to publish a
patch.

Thanks,
    Vitaly.

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