Messages in this thread | | | From | Dragan Cvetic <> | Subject | RE: [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl | Date | Tue, 19 Mar 2019 14:59:34 +0000 |
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> -----Original Message----- > From: Arnd Bergmann [mailto:arnd@arndb.de] > Sent: Tuesday 19 March 2019 13:18 > 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 1:05 PM Dragan Cvetic <dragan.cvetic@xilinx.com> wrote: > > > > Add char device interface per DT node present and support > > file operations: > > - open(), which keeps only one open per device at a time, > > - close(), which release the open for this device, > > - ioctl(), which provides infrastructure for a specific driver > > control. > > > drivers/misc/xilinx_sdfec.c | 79 ++++++++++++++++++++++++++++++++++++++++ > > include/uapi/misc/xilinx_sdfec.h | 4 ++ > > 2 files changed, 83 insertions(+) > > > > diff --git a/drivers/misc/xilinx_sdfec.c b/drivers/misc/xilinx_sdfec.c > > index a52a5c6..3407de4 100644 > > --- a/drivers/misc/xilinx_sdfec.c > > +++ b/drivers/misc/xilinx_sdfec.c > > @@ -81,8 +81,87 @@ struct xsdfec_dev { > > struct xsdfec_clks clks; > > }; > > > > +static int xsdfec_dev_open(struct inode *iptr, struct file *fptr) > > +{ > > + struct xsdfec_dev *xsdfec; > > + > > + xsdfec = container_of(iptr->i_cdev, struct xsdfec_dev, xsdfec_cdev); > > + if (!xsdfec) > > + return -EAGAIN; > > The result of container_of() will not be NULL here. > Did you mean to check i_cdev? That probably also won't > be NULL, but that check would be more reasonable.
Will be either removed fully or changed with i_cdev check
> > > + /* 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.
> Note that the test is not really atomic either: if three processes > try to open the file at the same time, it gets decremented from > 1 to -2, so only the second one sees 0 and increments it back > to -1 afterwards...
It looks you are right. Will fix this. Thank you for the catch.
> > > +static long xsdfec_dev_ioctl(struct file *fptr, unsigned int cmd, > > + unsigned long data) > > +{ > > + struct xsdfec_dev *xsdfec = fptr->private_data; > > + void __user *arg = NULL; > > + int rval = -EINVAL; > > + int err = 0; > > + > > + if (!xsdfec) > > + return rval; > > + > > + if (_IOC_TYPE(cmd) != XSDFEC_MAGIC) { > > + dev_err(xsdfec->dev, "Not a xilinx sdfec ioctl"); > > + return -ENOTTY; > > + } > > remove the error messages here as well. > > > + /* Access check of the argument if present */ > > + if (_IOC_DIR(cmd) & _IOC_READ) > > + err = !access_ok((void *)arg, _IOC_SIZE(cmd)); > > + else if (_IOC_DIR(cmd) & _IOC_WRITE) > > + err = !access_ok((void *)arg, _IOC_SIZE(cmd)); > > This seems odd. Why two separate checks, and why the access_ok() > check when you do a copy_from_user() that contains the same check > later?
Accepted, will remove it.
> > If you want to get fancy here, you could just copy the data in the main > ioctl handler based on _IOC_SIZE, and pass around normal kernel > pointers from there.
Will not be fancy. Thank you for the advice.
> > > static const struct file_operations xsdfec_fops = { > > .owner = THIS_MODULE, > > + .open = xsdfec_dev_open, > > + .release = xsdfec_dev_release, > > + .unlocked_ioctl = xsdfec_dev_ioctl, > > }; > > This lacks a .compat_ioctl pointer.
This is new for me, I have to investigate more and propose a solution. Thank you for suggestion.
> > Arnd
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