svn commit: r278320 - in head: contrib/mdocml lib lib/libdevctl share/mk sys/dev/acpica sys/dev/pci sys/kern sys/sys usr.sbin usr.sbin/devctl
Mateusz Guzik
mjguzik at gmail.com
Thu Feb 26 19:28:39 UTC 2015
On Thu, Feb 26, 2015 at 07:46:38AM -0500, John Baldwin wrote:
> On Thursday, February 26, 2015 12:40:06 AM Mateusz Guzik wrote:
> > On Fri, Feb 06, 2015 at 04:09:02PM +0000, John Baldwin wrote:
> > > Author: jhb
> > > Date: Fri Feb 6 16:09:01 2015
> > > New Revision: 278320
> > > URL: https://svnweb.freebsd.org/changeset/base/278320
> > >
> > > Log:
> > > Add a new device control utility for new-bus devices called devctl.
> > > This
> > > allows the user to request administrative changes to individual devices
> >
> > [..]
> >
> > > +static int
> > > +devctl2_ioctl(struct cdev *cdev, u_long cmd, caddr_t data, int fflag,
> > > + struct thread *td)
> > > +{
> > > + struct devreq *req;
> > > + device_t dev;
> > > + int error, old;
> > > +
> > > + /* Locate the device to control. */
> > > + mtx_lock(&Giant);
> > > + req = (struct devreq *)data;
> >
> > [..]
> >
> > > + switch (cmd) {
> >
> > [..]
> >
> > > + case DEV_SET_DRIVER: {
> > > + devclass_t dc;
> > > + char driver[128];
> > > +
> > > + error = copyinstr(req->dr_data, driver, sizeof(driver), NULL);
> >
> > [..]
> >
> > > + if (!driver_exists(dev->parent, driver)) {
> > > + error = ENOENT;
> > > + break;
> > > + }
> >
> > [..]
> >
> > > + }
> > > + mtx_unlock(&Giant);
> > > + return (error);
> > > +}
> >
> > I only skimmed thourgh this, will not a page fault drop + reacquire Giant
> > lock?
> >
> > iow, would not it be better to copy prior to taking the lock?
>
> It won't make a difference. All the logic is done after the copy, so it is
> still atomic.
>
Are devices guaranteed to be persistent?
find_device does ref them in any way, so i would assume that the dev you
found is only stable as long as Giant lock is held.
--
Mateusz Guzik <mjguzik gmail.com>
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