Erich Schubert wrote:
1. fifos.
The traditional approach is the /dev/initctl FIFO used by sysvinit.
This is a one-way link, and apps can lock() it to prevent interference
of write calls.
Minit does use two fifos, one for input, one for output. The semantics
is that you acquire a write lock on the "in" fifo (to init), then open
the "out" fifo for reading if you need/expect a reply. Example queries
are "give me the PID of service foo".
I don't know about runit or initng. Can someone please elaborate?
Afaict it has a plugin using sockets in /dev/initng (doesn't this
require a writeable filesystem?) and a plugin for initctl support.
Drawbacks:
- fifos need to be created before boot, so we don't need a writeable filesystem.
- only one client at a time
I think I read something like that:
server: open a read pipe A
client: create a bidirectional pipe B
client: sent info of this pipe B to server (with the pipe A)
server <-> client (via pipe B).
I don't remember the details (on Stevens?) but IIRC there
was a trick with unamed pipe, so it can be used concurrently
on boot (pre write fs) time.
ciao
cate
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