From: Arnd Bergmann <arnd@arndb.de>
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
Date: Tue, 19 Mar 2019 20:46:08 +0100 [thread overview]
Message-ID: <CAK8P3a01ufKsJxWNG09qeyLvVH12jiLpLchOxdKie0wzU2=WWQ@mail.gmail.com> (raw)
In-Reply-To: <BL0PR02MB5681C0D1D5DB5F57E3640D9ACB400@BL0PR02MB5681.namprd02.prod.outlook.com>
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.
Arnd
next prev parent reply other threads:[~2019-03-19 19:46 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-19 12:04 [PATCH 00/12] misc: xilinx sd-fec driver Dragan Cvetic
2019-03-19 12:04 ` [PATCH 01/12] dt-bindings: xilinx-sdfec: Add SDFEC binding Dragan Cvetic
2019-03-19 12:04 ` [PATCH 02/12] misc: xilinx-sdfec: add core driver Dragan Cvetic
2019-03-19 12:04 ` [PATCH 03/12] misc: xilinx_sdfec: Add CCF support Dragan Cvetic
2019-03-19 12:04 ` [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl Dragan Cvetic
2019-03-19 13:17 ` Arnd Bergmann
2019-03-19 14:59 ` Dragan Cvetic
2019-03-19 15:36 ` Arnd Bergmann
2019-03-19 18:10 ` Dragan Cvetic
2019-03-19 19:46 ` Arnd Bergmann [this message]
2019-04-09 8:35 ` Dragan Cvetic
2019-03-19 12:04 ` [PATCH 05/12] misc: xilinx_sdfec: Store driver config and state Dragan Cvetic
2019-03-19 12:04 ` [PATCH 06/12] misc: xilinx_sdfec: Add ability to configure turbo mode Dragan Cvetic
2019-03-19 12:04 ` [PATCH 07/12] misc: xilinx_sdfec: Add ability to configure LDPC Dragan Cvetic
2019-03-19 12:04 ` [PATCH 08/12] misc: xilinx_sdfec: Add ability to get/set config Dragan Cvetic
2019-03-19 13:05 ` Arnd Bergmann
2019-03-19 14:02 ` Dragan Cvetic
2019-03-19 12:04 ` [PATCH 09/12] misc: xilinx_sdfec: Support poll file operation Dragan Cvetic
2019-03-19 12:04 ` [PATCH 10/12] misc: xilinx_sdfec: Add stats & status ioctls Dragan Cvetic
2019-03-19 12:04 ` [PATCH 11/12] Docs: misc: xilinx_sdfec: Add documentation Dragan Cvetic
2019-03-19 12:04 ` [PATCH 12/12] MAINTAINERS: add maintainer for SD-FEC support Dragan Cvetic
2019-03-19 12:17 ` [PATCH 00/12] misc: xilinx sd-fec driver Michal Simek
2019-03-19 13:44 ` Dragan Cvetic
2019-03-19 13:51 ` Michal Simek
2019-03-19 13:55 ` Dragan Cvetic
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