[9fans] userspace netlog style log file in fs?

[9fans] userspace netlog style log file in fs?

[Axel Belinfante]

I'm turning my 802.1x thingy into an fs, using 9p(2),
and I'm now looking into adding a netlog-style
log file such that you can just 'cat /net/8021x/log'
and it will hang there in read until stuff is
added to the log. multiple readers should see
the same stuff.

I guess this amounts to
 - keeping a ring buffer of log messages (a la netlog)
 - keeping a queue of 'pending' read's --
   read is the only thing for which completion
   may have to be delayed, right?
 - pending reads should 'complete' when stuff
   is logged (i.e. something to read appears)
 - pending reads should be cleaned away
   when the fid is clunked
 - deal with flushes?
 - deal with slow readers that read slower
   than the log gets updated, i.e. at a certain
   moment they may ask for data that already has
   been overwritten

I found inspiration in /sys/src/9/ip/netlog.c and
/sys/src/cmd/ssh/sshnet.c
(and other places mentioned in 9p(2))
Are there other things I might want to look at?
Are there particular traps I might want to avoid,
things to think of?

Sorry for these a bit vague, 'open' questions -
I'm sure I'll succeed to figure things out myself,
but if people have been there already I'd rather
not reinvent the wheel.
Also, I could imagine that such logging stuff might
be useful for other programs, if it could be
integrated easily.

Axel.

Re: [9fans] userspace netlog style log file in fs?

[Russ Cox]

> I guess this amounts to
>  - keeping a ring buffer of log messages (a la netlog)
>  - keeping a queue of 'pending' read's --
>    read is the only thing for which completion
>    may have to be delayed, right?

Yes.

>  - pending reads should 'complete' when stuff
>    is logged (i.e. something to read appears)
>  - pending reads should be cleaned away
>    when the fid is clunked
>  - deal with flushes?

Yes!  Otherwise you can't kill a process that is blocked
reading the log file.

>  - deal with slow readers that read slower
>    than the log gets updated, i.e. at a certain
>    moment they may ask for data that already has
>    been overwritten

Tough for them.

> I found inspiration in /sys/src/9/ip/netlog.c and
> /sys/src/cmd/ssh/sshnet.c

See also /sys/src/9/port/log.c.  Sshnet is a good example
of getting the flushes right.

Russ