On 13.03.2015 21:43, Laurent Bercot wrote:
Except you have to make the writes blocking, which severely limits
what the writers can do - no asynchronous event loop. For a simple
"cat"-equivalent between the netlink and a fifo, it's enough, but
it's about all it's good for. And such a "cat"-equivalent is still
useless.
I'm using none blocking I/O and expect handling of failure situations,
e.g writing into pipe fails with EAGAIN: poll wait until write possible
with timeout. then redo write
It's still a very bad idea to allow writes from different sources
into a single fifo when there's only one authoritative source of data,
in this case the netlink.
Ohps!?
one netlink daemon -> pipe -> parser
or
many hotplug helper -> pipe -> parser
If a process wants to read uevents from a
pipe, it can simply read from an anonymous pipe, being spawned by the
netlink listener. That's what my s6-uevent-listener and Natanael's
nldev do, and I agree with you: there's simply no need to introduce
fifos into the picture.
Laurent, you still stuck on netlink! Using named pipe is requirement for
the hotplug helper stuff, how else should they get access to the pipe,
when not using a named pipe? And what is the difference between fifos
and pipes?
from "man 7 pipe":
---snip---
Pipes and FIFOs (also known as named pipes) provide a unidirectional
interprocess communication channel. A pipe has a read end and a write
end. Data written to the write end of a pipe can be read from the read
end of the pipe.
---snip---
You see? So whey is pipe good (your choice) and fifo bad (mine)? They
differ only in how to get access to the descriptors.
--
Harald
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