Re: [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl

[Arnd Bergmann]

On Tue, Mar 19, 2019 at 3:59 PM Dragan Cvetic <draganc@xxxxxxxxxx> wrote:
> >
> > > +       /* Only one open per device at a time */
> > > +       if (!atomic_dec_and_test(&xsdfec->open_count)) {
> > > +               atomic_inc(&xsdfec->open_count);
> > > +               return -EBUSY;
> > > +       }
> >
> > What is that limitation for? Is it worse to open it twice than
> > to dup() or fork()?
> >
> The device can be opened only once.

What I mean here is that preventing the double open() is
a fairly weak protection: it means you cannot have multiple
'struct file' pointers attached to the same inode, but you
can still have the same 'struct file' being available to
multiple processes.

         Arnd