kqueue and device driver experience anyone ?
rizzo at iet.unipi.it
Fri Aug 26 15:42:09 UTC 2011
a question for the kqueue experts out there:
I am trying to add kqueue support to a device driver, and am puzzled
on what the .f_event() function may assume.
I see that some of the examples (e.g. bpf, audit_pipe.c)
expect that the function is called with the device lock held
(and even have a LOCK_ASSERT).
Others (if_tap, cam/scsi/scsi_target.c) either do not use the lock
or explicitly acquire it.
As far as i can tell the .f_event() function is called in two places:
- within knote() which in turn (through KNOTE_*() ) is called
by the driver itself near selrecord() . So it is up to the
device driver to call it with the device lock held;
- within kqueue_scan(), which instead is called from the upper half
of the kernel as part of kern_kevent(). Here there seems to be no
way that the device lock is acquired when .f_event() is called.
Unless, of course, the knote's on which these .f_event() are
called are not the same ones attached to devices -- so there is
a different .f_event() function called ?
So, is there a bug in the kqueue support for bpf.c and audit_pipe.c,
or i am missing something important ?
More information about the freebsd-current