Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 19 Mar 2019 14:17:45 +0100 | Subject | Re: [PATCH 04/12] misc: xilinx_sdfec: Add open, close and ioctl |
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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.
> + /* 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()?
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...
> +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?
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.
> 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.
Arnd
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