On Mon, Mar 9, 2015 at 9:41 AM, Natanael Copa <nc...@alpinelinux.org> wrote: > On Sun, 08 Mar 2015 16:10:32 +0100 > Harald Becker <ra...@gmx.de> wrote: >> I'm currently in the phase of thinking about extending the functionality >> of mdev. As here are the experts working with this kind of software, I >> like to here your ideas before I start hacking the code. > > ... > >> 2) I like to use netlink to obtain hotplug information and avoid massive >> respawning of mdev as hotplug helper when several events arrive quickly. > > I am interested in a netlink listener too for 2 reasons: > > - serialize the events > - reduce number of forks for perfomance reasons > >> That is, I want to auto fork a daemon which just open the netlink >> socket. When events arrive it forks again, creating a pipe. The new >> instance read mdev.conf, build a table of rules in memory, then read >> hotplug operations from the pipe (send by the first instance). When >> there are no more events for more then a few seconds, the first instance >> closes the pipe and the second instance exits (freeing the used memory). >> On next hotplug event a new pipe / second instance is created. > > I have a simlar idea, but slightly different. I'd like to separate the > netlink listener and the event handler. > > I am thinking of using http://git.r-36.net/nldev/ which basically does the > same thing as s6-devd: minimal daemon that listens on netlink and for > each event it fork/exec mdev. > > What I'd like to do is: > > change mdev to: > - be able to read events from stdin. same format as from netlink socket. > - set a timeout on stdin (1 sec or so by default). when time out is > reached (no event within a sec) then just exit. > > change nldev to: > - have a mdev pipe fd which we forward the kernel events to. > - on kernel event > if mdev_pipe_fd is -1 then: > create pipe, fork and exec mdev with args to have > mdev read from stdin (as explained above) > else: > write the kernel event to the pipe fd > > - the mdev pipe fd is added to the poll(2) call so we catch POLLHUP to > detect mdev timeout. When that happens, set the mdev pipe fd to -1 so > we know that it needs to be respawned on next kernel event. > > The benifits: > - the netlink listener who needs to be running all times is very > minimal. > > - when there are many events within short time, (eg coldplugging), we > avoid the many forks and gain performance. > > - when there are no events, mdev will timeout and exit. > > - busybox mdev does not need set up netlink socket. (less intrusive > changes in busybox)
But that nldev process will exist for all time, right? That's not elegant. Ideally, this respawning logic should be in the kernel. _______________________________________________ busybox mailing list busybox@busybox.net http://lists.busybox.net/mailman/listinfo/busybox
