Char device initialization

Char device initialization

[Daniel Hilst Selli]

I'm trying to create a example char device. The example compiles fine, 
but when I try to "cat" I got "No such device or address". I have
reviewed the code thousend times and can't see what I'm missing

Here is the code -> http://pastebin.com/Td03U0fK

The read method is not good, I know, but is never called.

I use my own running kenrel to test, I know that is danger. I'm building 
a qemu enviroment to test this better.

Here is uname -a:
Linux archlinux 3.0-ARCH #1 SMP PREEMPT Fri Oct 7 11:35:34 CEST 2011 
x86_64 Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz GenuineIntel GNU/Linux

Any idea?

Thanks

Char device initialization

[Alexandru Juncu]

On Wed, Nov 9, 2011 at 3:41 PM, Daniel Hilst Selli
<danielhilst@gmail.com> wrote:
> I'm trying to create a example char device. The example compiles fine,
> but when I try to "cat" I got "No such device or address". I have
> reviewed the code thousend times and can't see what I'm missing
>
> Here is the code -> http://pastebin.com/Td03U0fK
>
> The read method is not good, I know, but is never called.
>
> I use my own running kenrel to test, I know that is danger. I'm building
> a qemu enviroment to test this better.
>
> Here is uname -a:
> Linux archlinux 3.0-ARCH #1 SMP PREEMPT Fri Oct 7 11:35:34 CEST 2011
> x86_64 Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz GenuineIntel GNU/Linux
>
> Any idea?
>
> Thanks

You tried to 'cat' a /dev/my_device file, right?
Was that device file created with the mknod command?

-- 
Alexandru Juncu

ROSEdu
http://rosedu.org

Char device initialization

[rohan puri]

On Wed, Nov 9, 2011 at 7:22 PM, Alexandru Juncu <alex.juncu@rosedu.org>wrote:

> On Wed, Nov 9, 2011 at 3:41 PM, Daniel Hilst Selli
> <danielhilst@gmail.com> wrote:
> > I'm trying to create a example char device. The example compiles fine,
> > but when I try to "cat" I got "No such device or address". I have
> > reviewed the code thousend times and can't see what I'm missing
> >
> > Here is the code -> http://pastebin.com/Td03U0fK
> >
> > The read method is not good, I know, but is never called.
> >
> > I use my own running kenrel to test, I know that is danger. I'm building
> > a qemu enviroment to test this better.
> >
> > Here is uname -a:
> > Linux archlinux 3.0-ARCH #1 SMP PREEMPT Fri Oct 7 11:35:34 CEST 2011
> > x86_64 Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz GenuineIntel GNU/Linux
> >
> > Any idea?
> >
> > Thanks
>
> You tried to 'cat' a /dev/my_device file, right?
> Was that device file created with the mknod command?
>
> --
> Alexandru Juncu
>
> ROSEdu
> http://rosedu.org
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>


Hello Daniel,

I had the look at the code. The issue is with the cdev_add() call in
init_gcdev() function.

int cdev_add(struct cdev *p, dev_t dev, unsigned count) is the prototype

Now the problem was  *instead of passing second argument of type dev_t you
were passing minor number macro.

*Fix : - Do following additions : -

1. static int major; // Declare a global major no var.

2. In init_gcdev() after call to alloc_chrdev_region() get major no and
store in major var.

major = MAJOR(gcdev->dev);

3. Replace cdev_add() call like this : -

 cdev_add(&gcdev->cdev, MKDEV(major, FIRST_MINOR), 1);

Now its running and your read methos is getting called.

Hello Alexandru,

That error was due to improper args passed to cdev_add(). If device file is
not present (no mknod done) error would be "No such file or dir"

Regards,
Rohan Puri
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Char device initialization

[Daniel Hilst Selli]

On 11/09/2011 01:28 PM, rohan puri wrote:
>
>
> On Wed, Nov 9, 2011 at 7:22 PM, Alexandru Juncu <alex.juncu@rosedu.org
> <mailto:alex.juncu@rosedu.org>> wrote:
>
>     On Wed, Nov 9, 2011 at 3:41 PM, Daniel Hilst Selli
>     <danielhilst at gmail.com <mailto:danielhilst@gmail.com>> wrote:
>      > I'm trying to create a example char device. The example compiles
>     fine,
>      > but when I try to "cat" I got "No such device or address". I have
>      > reviewed the code thousend times and can't see what I'm missing
>      >
>      > Here is the code -> http://pastebin.com/Td03U0fK
>      >
>      > The read method is not good, I know, but is never called.
>      >
>      > I use my own running kenrel to test, I know that is danger. I'm
>     building
>      > a qemu enviroment to test this better.
>      >
>      > Here is uname -a:
>      > Linux archlinux 3.0-ARCH #1 SMP PREEMPT Fri Oct 7 11:35:34 CEST 2011
>      > x86_64 Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz GenuineIntel
>     GNU/Linux
>      >
>      > Any idea?
>      >
>      > Thanks
>
>     You tried to 'cat' a /dev/my_device file, right?
>     Was that device file created with the mknod command?
>
>     --
>     Alexandru Juncu
>
>     ROSEdu
>     http://rosedu.org
>
>     _______________________________________________
>     Kernelnewbies mailing list
>     Kernelnewbies at kernelnewbies.org <mailto:Kernelnewbies@kernelnewbies.org>
>     http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
>
> Hello Daniel,
>
> I had the look at the code. The issue is with the cdev_add() call in
> init_gcdev() function.
>
> int cdev_add(struct cdev *p, dev_t dev, unsigned count) is the prototype
>
> Now the problem was *instead of passing second argument of type dev_t
> you were passing minor number macro.
>
> *Fix : - Do following additions : -
>
> 1. static int major; // Declare a global major no var.
>
> 2. In init_gcdev() after call to alloc_chrdev_region() get major no and
> store in major var.
>
> major = MAJOR(gcdev->dev);
>
> 3. Replace cdev_add() call like this : -
>
>   cdev_add(&gcdev->cdev, MKDEV(major, FIRST_MINOR), 1);
>
> Now its running and your read methos is getting called.
>
> Hello Alexandru,
>
> That error was due to improper args passed to cdev_add(). If device file
> is not present (no mknod done) error would be "No such file or dir"
>
> Regards,
> Rohan Puri
Thanks Rohan, my fault!