Regards,
Sandeep.
Hi Pie,
“To learn is to change. Education is a process that changes the learner.”
On Mon, Jul 13, 2009 at 11:31 AM, Pei Lin <telent...@gmail.com> wrote:
> Is it different?
>
Yes. they are.
> let us see the typedef about this two.
> user space: unsigned long int
> kernel space :
> typedef __u32 __kernel_dev_t;
> typedef __kernel_dev_t dev_t;
>
> "long int " in 64bit cpu should be 8 bytes
>
[12:02:21 sinhas]$ ./a.out
unsigned long int size = 4
dev_t size = 8
unsigned long size = 4
int size = 4[~]
[12:02:24 sinhas]$
So, here long is 32bits on 32 bit and 64 bits on 64 bit.
Where did you get the definition of dev_t to be unsigned long int?
Its defined as unsigned long long
dev_t ->__dev_t -> __STD_TYPE __DEV_T_TYPE __dev_t; -> # define
__STD_TYPE __extension__ typedef ->
__extension__ typedef signed long long int __int64_t;
__extension__ typedef unsigned long long int __uint64_t;
>
> So i think in 32 bit cpu they are same,and if your kernel compile for
> 32 and user space configuration for 64.....
> Is it the problem ?
>
Explained above.
>
> BRs,
>
> Lin
>
> 2009/7/13 SandeepKsinha <sandeepksi...@gmail.com>:
> > Hi Greg,
> >
> > find my reply inline.
> >
> > On Sun, Jul 12, 2009 at 11:44 PM, Greg KH <g...@kroah.com> wrote:
> >>
> >> On Sun, Jul 12, 2009 at 10:16:17PM +0530, SandeepKsinha wrote:
> >> > Hi,
> >> > to my surprise,
> >> > the sizeof dev_t differs in userspace and kernel.
> >> > Its 8 bytes in userspace and 4bytes in kernel.
> >> >
> >> > I am working on a driver, where I include the headers in both user and
> >> > kernel space.
> >> > And I get wrong values due to the difference in sizes.
> >> >
> >> > How do I handle such a situation ?
> >>
> >> Why would you be passing a dev_t from user to kernel space as a binary
> >> value?
> >
> > I am not passing a dev_t as a binary from userspace to kernel space.
> > Its a part of the structure.
> >
> > E.g
> >
> > struct device_info {
> >
> > dev_t dev_num;
> > ...
> > ....
> > }
> >
> >
> >>
> >> Why do you want to pass such a value across the boundry in the first
> >> place?
> >
> > This is pretty much for a custom driver, where I perform the following.
> > 1. Parse the information in user space from a XML file
> > 2. Do a stat on the device,
> > 3. extract the device number
> > 4. Fill in the structure
> > 5. Pass it to the kernel driver using ioctl.
> >
> > Reference: OHSM : http://code.google.com/p/fscops/
> >
> >>
> >> Could you describe what the problem is you are trying to sove by doing
> >> this?
> >
> > Its just a part of my implementation. And I wanted to keep this uniform
> > across the system.
> > But having such discrepancies really disappointed me.
> >
> > But I still don't understand the philosophy behind having different sizes
> > for dev_t in user and kernel space.
> > And most importantly, its not documented and it eventually leads to
> silent
> > corruption. Which is real difficult to trace in complex systems.
> >
> >
> >>
> >> thanks,
> >>
> >> greg k-h
> >
> > Regards,
> > Sandeep.
> >
> >
> > “To learn is to change. Education is a process that changes the learner.”
> >
>
