idea: user to user pipe copy

[Mark Borgerding <mark@borgerding.net>]

Would someone tell me why this
a) won't work?
b) shouldn't be done?
c) is the dumbest idea since Microsoft Bob?


Currently, piped data gets copied from user space to a kernel buffer 
then back out to user space. 

This happens regardless of whether there is already a reader who is 
blocked on that fd.

Instead ...

Why not keep track of blocked read()s on a pipe fd?

When the writer writes something to the pipe, data could be copied 
directly from one user process to another, rather than
calling copy_from_user then copy_to_user. 

This alleged speed increase would benefit all blocking pipes & fifos, 
roughly half the time (i.e. whenever the read happens before the write).

-- Mark Borgerding