bug#9089: [1003.1(2008)/Issue 7 0000205]: Shell pipeline connection requirement too vague

[Jonathan Nieder]

Glenn Fowler wrote:

> we need a standard way to peek read data on a pipe without blocking
> or consuming the data
>
> we use ioctl(I_PEEK) on pipe() on systems that feature test ok for that
> and if not then recv(MSG_PEEK) on socketpair()
> otherwise the much slower "cant't peek pipe data" code kicks in
>
> rather than getting stuck on using a socket api for pipes
> can we first determine that peeking pipe read data is useful
> and then determine an api

Yes, sorry for the lack of clarity on my part.  Being able to peek
ahead when reading from a pipe would be very useful imho.  All I meant
is that and I was sloppy about the words used (i.e., the details of
the API do not matter much).

I will try to find time to mock up a pipe_peek() syscall (just as a
prototype) for Linux some time this week.  I would be happy if people
on other platforms without support for this (and others on Linux, too)
try something similar so we can compare notes and decide what to
standardize on.

Thanks.