Re: kern/58869: ipmi(4) holds sc_cmd_mtx across copyout, needed for wdog tickle

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Fix:
> Narrow the scope of sc_cmd_mtx in ipmi_ioctl to
> ipmi_sendcmd/recvcmd, not malloc/copyin/copyout.

Oops -- it's not quite that simple because there's also a longer-term
lock, sc_mode.  Need to work around that too.

This is a bit troublesome because in the /dev/ipmi0 ioctl interface,
when userland invokes ioctl(IPMICTL_SEND_COMMAND) it blocks watchdog
tickles until userland later invokes ioctl(IPMICTL_RECEIVE_MSG).

It seems to me either

(a) there should just be a combined ioctl for send/recv (but I have no
    idea how widespread this ioctl interface is, maybe it's used by
    important applications like sysutils/ipmitool so we can't just
    remove IPMICTL_SEND_COMMAND and IPMICTL_RECEIVE_MSG); or

(b) IPMICTL_SEND_COMMAND should do ipmi_recvmsg and save it in a
    buffer for the next IPMICTL_RECEIVE_MSG; or

(c) if ipmi_recvmsg might take longer than IPMICTL_SEND_COMMAND is
    supposed to wait, it should be deferred to an asynchronous thread
    so the watchdog tickle is only held up by the ipmi(4)
    responsiveness and not by arbitrary userland dawdling.