lkml.org 
[lkml]   [2019]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl
Date


> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@arndb.de]
> Sent: Tuesday 19 March 2019 19:46
> To: Dragan Cvetic <draganc@xilinx.com>
> Cc: gregkh <gregkh@linuxfoundation.org>; Michal Simek <michals@xilinx.com>; Derek Kiernan <dkiernan@xilinx.com>; Linux ARM
> <linux-arm-kernel@lists.infradead.org>; Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl
>
> On Tue, Mar 19, 2019 at 7:10 PM Dragan Cvetic <draganc@xilinx.com> wrote:
> > > -----Original Message-----
> > > From: Arnd Bergmann [mailto:arnd@arndb.de]
> > > Sent: Tuesday 19 March 2019 15:36
> > > To: Dragan Cvetic <draganc@xilinx.com>
> > > Cc: gregkh <gregkh@linuxfoundation.org>; Michal Simek <michals@xilinx.com>; Linux ARM <linux-arm-
> kernel@lists.infradead.org>;
> > > Derek Kiernan <dkiernan@xilinx.com>; Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
> > > Subject: Re: [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl
> > >
> > > On Tue, Mar 19, 2019 at 3:59 PM Dragan Cvetic <draganc@xilinx.com> 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.
> > >
> > Could you please suggest the solution?
> > My intention was to prevent more than one process access the same device.
>
> Generally speaking, you can't prevent it, but you should make sure that
> if two processes attempt to use the same device, nothing bad happens.
> Usually it's enough to have appropriate locking.
>
There is a need to increase the driver security, even the proposed is not perfect,
it is acceptable for us for now.

> Arnd
\
 
 \ /
  Last update: 2019-04-09 10:36    [W:0.061 / U:5.536 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site