On Fri, 26 Jun 1998 04:37:02 +0200 (MET DST), MOLNAR Ingo
<mingo@valerie.inf.elte.hu> said:
> On 25 Jun 1998, Stephen C. Tweedie wrote:
>> At the Expo, Larry McVoy made a suggestion that we allow reads and
>> writes to specify some form of token to identify the data being
>> transfered, without actually having to make the data visible in user
>> space at all.
> why cannot this 'token' be a file descriptor (like in Linus's suggestion)?
> Is there any valid case where we cannot associate 'stuff to be
> transferred' with a 'file'?
The token itself is not a file descriptor: it represents some data
read from a file descriptor.
Just as we already have readv and writev to do IO to an iovec in user
space, Larry is proposing a pull/push mechanism which does IO to an
iovec in physical kernel memory, to/from an existing open fd. The
token is just the thing returned by the kernel to identify the
particular iovec generated by a pull().
In other words, the mechanism is just like existing reads and writes
with file descriptors, except that the data never enters user space
and so the kernel has to provide the write mechanism with an
alternative name space for the user to identify the data with.
--Stephen
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