On Wed, 19 Jan 2000 almesber@lrc.di.epfl.ch wrote:
> Recently, we had a discussion on the linux-atm list about the best approach
> for passing kernel pointers to user space, and back. The idea is as follows:
[SNIPPED...]
A pointer in user space is not a pointer in kernel space! Kernel data
is referenced by a discriptor, referenced as KERNEL_DS, which is not
accessible from user-mode privilege.
You can use mmap() to map kernel data (if you know where it is) to
user-space. However, modification from user-mode code will give
problems with atomicity.
If you need to access to kernel data, you should use an installable
module. Here, the mapping to KERNEL_DS is done for you, and you
can copy_from_user(), copy_to_user(), with the required translation
and, paging done for you. Typical copy using read() from a device
driver runs at between 300 to 750 megabytes per second, depending
upon the CPU, speed, and cache characteristics.
Cheers,
Dick Johnson
Penguin : Linux version 2.3.39 on an i686 machine (800.63 BogoMips).
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