Re: Issue with ioctl commands - Linux version 2.6.35.7+

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On 12/27/11, Alexandru Juncu <alex.juncu@xxxxxxxxxx> wrote:
> On Tue, Dec 27, 2011 at 1:57 PM, Chetan Nanda <chetannanda@xxxxxxxxx> wrote:
>>
>>
>> On Tue, Dec 27, 2011 at 5:23 PM, Alexandru Juncu <alex.juncu@xxxxxxxxxx>
>> wrote:
>>>
>>> On Tue, Dec 27, 2011 at 1:39 PM, Chetan Nanda <chetannanda@xxxxxxxxx>
>>> wrote:
>>> > Hi All,
>>> >
>>> > I am facing a strange issue with the ioctl commands, and not able to
>>> > find
>>> > what wrong I am doing.
>>> > I am trying with a dummy kernel driver and implemented ioctl command as
>>> > follow:
>>> >
>>> > in my_ioctl.h
>>> > #define READHWREG_MAGIC_NUMBER 0x15
>>> > #define READHWREG_CAM_READPE _IOR(READHWREG_MAGIC_NUMBER, 1, int*)
>>> >
>>> > But the value of 'READHWREG_CAM_READPE' is comes out to be different in
>>> > userspace (in the application) and kernel space (in the driver).
>>> >
>>> > In userspace I used ioctl as
>>> > ...
>>> >    printf("\ncommand %x \n",READHWREG_CAM_READPE); <-- command 80041501
>>> >    error = ioctl(g_DevFileId, READHWREG_CAM_READPE);
>>> > ..
>>> >
>>> > In kernel space
>>> >
>>> > int readHwReg_ioctl(struct inode *node, struct file *filp, unsigned int
>>> > cmd,  unsigned long arg)
>>> > {
>>> > ...
>>> >    printk("\n%d %s cmd = %x\n",__LINE__,__FUNCTION__,cmd); <--- cmd =
>>> > bee6a9d4
>>> > ...
>>> > }
>>> >
>>> >
>>> > I am not able to figure out the root cause,
>>> > Please help to check...
>>>
>>> I think that the command is actually sent via the arg parameter, which
>>> is an address (it's a pointer to the value your are sending to kernel
>>> space).
>>
>>
>> Yes, even I observe this now. But how this can happen.
>> 'command' is the second argument for ioctl call.
>
> As far as I remember, you can send an integer through the cmd, but
> other things (like structures or buffers) through their address (and
> copy_from_user-ed). But, maybe, on new implementations (or on some
> architectures) everything is send via address.

What I have observed, third argument of the ioctl system call is
reaching the driver as a command.
ioctl(g_DevFileId, READHWREG_CAM_READPE, xx);

In driver:
int readHwReg_ioctl(struct inode *node, struct file *filp, unsigned
int cmd,  unsigned long arg)
cmd is equal to xx

Am I missing something in the driver/application.

Thanks,
Chetan Nanda

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