lkml.org 
[lkml]   [2021]   [Feb]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v8 18/22] docs: counter: Document character device interface
On Mon, Feb 22, 2021 at 11:11:33AM +0100, Pavel Machek wrote:
> Hi!
>
> > > +* COUNTER_ENABLE_EVENTS_IOCTL:
> > > + Enables monitoring the events specified by the Counter watches that
> > > + were queued by ``COUNTER_ADD_WATCH_IOCTL``. If events are already
> > > + enabled, the new set of watches replaces the old one. Calling this
> > > + ioctl also has the effect of clearing the queue of watches added by
> > > + ``COUNTER_ADD_WATCH_IOCTL``.
> > > +
> > > +* COUNTER_DISABLE_EVENTS_IOCTL:
> > > + Stops monitoring the previously enabled events.
> >
> > Is there a way to remove a watch?
>
> Is there a way to eat all kernel memory and crash the system by adding
> too many watches?

There can only ever be as many watches as there are Counter components
for the respective Counter device. This is enforced by
counter_set_event_node() which checks whether a particular watch has
been created before and returns an EINVAL if it so has.

> > > +For example, the following userspace code opens ``/dev/counter0``,
> > > +configures the ``COUNTER_EVENT_INDEX`` event channel 0 to gather Count 0
> > > +and Count 1, and prints out the data as it becomes available on the
> > > +character device node::
> > > +
> >
> > Consider adding an example program under tools/
> >
> > > + #include <fcntl.h>
> > > + #include <linux/counter.h>
> > > + #include <stdio.h>
> > > + #include <string.h>
> > > + #include <sys/ioctl.h>
> > > + #include <unistd.h>
> > > +
> > > + struct counter_watch watches[2] = {
> > > + {
> > > + .component.type = COUNTER_COMPONENT_COUNT,
> > > + .component.scope = COUNTER_SCOPE_COUNT,
> > > + .component.parent = 0,
> >
> > Good to add comments on what these elements actually are?
>
> > > + fd = open("/dev/counter0", O_RDWR);
> > > +
> > > + ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches);
> > > + ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches + 1);
> > > + ioctl(fd, COUNTER_ENABLE_EVENTS_IOCTL);
>
> > > + for (;;) {
> > > + read(fd, event_data, sizeof(event_data));
>
> If this goes to tools it really should have error handling and
> handling of short read.
>
> Best regards,
> Pavel
>
> --
> http://www.livejournal.com/~pavelmachek

Ack. I'll improve the error handling for this.

William Breathitt Gray
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2021-02-26 01:29    [W:0.077 / U:2.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site