On Sun, Nov 19, 2000 at 07:24:16PM +0900, GOTO Masanori wrote:
> At Mon, 13 Nov 2000 11:13:19 -0500,
> Jakub Jelinek <jakub@redhat.com> wrote:
> > ago were done in the kernel, POSIX message queue passing is not doable in
> > userland without kernel help either (I have a message queue filesystem
> > kernel patch for this, but it is a 2.5 thing).
>
> Interesting. Is yours ready for?
> (I'm also working with it. I agree it's for 2.5)
Below is my preliminary version from Sep, 16th if you're interested.
I haven't had time for it since then, so it most probably will not apply
cleanly to current kernel.
Things still to do:
- clean it up
- implement poll on message queues
- handle __SI_RT in architectural copy_siginfo_to_user routines
- test much more than I have done so far
- fix mq_notify - see below
- avoid doing linear searches - see below
Message queues are presented as a new filesystem, mounted usually on
/dev/msg. The objects in that filesystems are fifos with special MQ
semantics.
One can use normal open/read/write on fifos in /dev/msg, which
means mq_open with mq_attr NULL, mq_receive which does not tell the priority
and mq_send with default priority.
Then there are a few ioctls which allow to open with special queue
attributes, send with priority and receive so that you get priority back,
etc.
Things I'm not sure about is mq_notify, because it states the signal should
be sent to the process (ie. I'd think it is tgid, not pid in 2.4.0-test8,
but then I don't know which close/exit should cause the notification
registration to be freed).
Also, I wonder how many pending messages typical message queues have
pending, if not too many, then the current linear search is fine, otherwise
I should put the messages into some heap which would allow O(1) mq_receive.
If you find any races/problems, please let me know.
I've coded mqueue.h public glibc userland header and mqueue.c which has
hacks on top and then basically what could end up in glibc's mq_*.c (after
shm_open.c code for locating mount points is copied in).
Jakub
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