Re: Seekable pipes

[Richard Patterson]

Jan,

> > I want to implement an interface for seekable
pipes
> > (and FIFOs) in the Linux kernel.

> Why not simply create two pipes, and use one for the
> data (from writer to reader) and the other for 
> control (r->w)? Then you would  not need to poke
> with the kernel after all.

The idea is that the reading side dosen't know it's a
pipe -- thus this interface can be used to provide
file-like access to non-filesystem objects like HTTP
files or Postgres large objects. With kernel support,
the reading side can be unaware that it is reading
from a pipe -- it just seeks. So you can do wierd
things like wget http://stuff/stuff.pdf | xpdf
/dev/stdin -- even though xpdf doesn't support piped
input.

However, Chris Siebenmann pointed out that a file
descriptor can be passed to other processes with
fork() or domain sockets -- thus the writer side of
the pipe would have to support multiple readers with
distinct positions. Which is a lot hairer than the
interface I outlined earlier.

Cheers,

--Ian Turner


		
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