Re: 2.4 in-kernel file opening

["linux-os \(Dick Johnson\)" <linux-os@analogic.com>]

On Tue, 4 Oct 2005, Martin Drab wrote:

> Hi,
>
> can anybody tell me why there is no sys_open() exported in kernel/ksyms.c
> in 2.4 kernels while the sys_close() is there? And what is then the
> preferred way of opening files from within a 2.4 kernel module?
>
> Thank you,
> Martin

There is no way to open files within the kernel. Any attempt is
just a hack. The kernel is designed to perform tasks on behalf
of the caller. It doesn't have a context. It uses the caller's
context. A file-descriptor is a number that relates to the
current context. i.e., STDIN_FILENO is __different__ for you
and somebody else, even though it has the same numerical value.

To open a file in the kernel requires either a task with a
context (like a kernel thread) or you have to steal the context
of somebody which can destroy some innocent task's context.

You are never supposed to use files inside the kernel; period!
If you need to obtain file-data for a driver or receive file-
data from a driver, we have read(), write(), mmap(), and ioctl()
to accomplish these things from user-mode. A user-mode program can
write data directly to your driver using mmap(), for instance.
Or it can use a function-code you define to upload/download data
using ioctl().

This is a FAQ. Many persons have rejected this advice, only
to later on modify their drivers to correspond to the correct
way of writing Unix/Linux device drivers. This, after they've
trashed many innocent tasks.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13 on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.

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Thank you.
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