Standards Update, IEEE 1003.4: Real-time Extensions

Chip Salzenberg chip at tct.uucp
Thu Aug 30 22:31:01 AEST 1990

From:  chip at tct.uucp (Chip Salzenberg)

According to sp at (Simon Patience):
>Some realtime embedded systems do not have a file system but do want
>semaphores.  So this allows them to have them without having to bring
>in the baggage a file system would entail.

I was under the impression that POSIX was designing a portable Unix
interface.  Without a filesystem, you don't have Unix, do you?
Besides, a given embedded system's library could easily emulate a
baby-simple filesystem.

>Secondly, as far as threads, which are supposed to be light weight,
>are concerned it allows semaphores to be implmented in user space
>rather than forcing them into the kernel for the file system.

The desire for user-space support indicates to me that there should be
some provision for non-filesystem (anonymous) IPCs that can be created
and used without kernel intervention.  This need does not reduce the
desirability of putting global IPCs in the filesystem.

>A good reason for *not* having IPC handles in the file system is to allow
>network IPC to use the same interfaces.

Filesystem entities can be used to trigger network activity by the
kernel (or its stand-in), even if they do not reside on shared
Chip Salzenberg at Teltronics/TCT     <chip at tct.uucp>, <uunet!pdn!tct!chip>

Volume-Number: Volume 21, Number 74

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