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SubjectRe: [PATCH] Lightweight userspace semaphores...

On Sat, 23 Feb 2002, Rusty Russell wrote:

> 1) Interface is: open /dev/usem, pread, pwrite.

i like the patch, but the interface is ugly IMO. Why not new syscalls? I
think these lightweight semaphores will become an important part of Linux,
so having their own syscall entries is the most correct interface,
something like:

sys_sem_create()
sys_sem_destroy()
sys_sem_down()
sys_sem_up()

/dev/usem is such an ... ioctl()-ish approach. It's a scalability problem
as well: read()/write() has (or can have) some implicit locking that is
imposed on the usem interface as well. It's a usage robustness issue as
well: chroot() environments that have no /dev directory will suddenly lose
a functionality of Linux. There is absolutely no problem with adding new
syscalls for things like this.

Plus sys_sem_create() should do some proper resource limit management,
pinning down an unlimited number of pages is bad.

Ingo

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