> >>From: "Richard B. Johnson" <root@chaos.analogic.com>
> >>Reply-To: root@chaos.analogic.com
> >>To: Praveen <praveenb@trinc.com>
> >>cc: linux-kernel@vger.rutgers.edu
> >>Subject: Re: Open file in kernel Mode...
> >>
> >>On Wed, 24 May 2000, Praveen wrote:
> >>
> >>> Hi folks,
> >>> I want to open the file in init module..
> >>> Following is the piece of code i tried..Have a look it...
> >>>
> >>> open=sys_call_table[__NR_open];
> >>> fd=(*open) ("/dev/tty",0,0);
> >>>
> >>> But open system call is returning error value ( -14).
> >>>
> >>> Even i tried to read from standard input fd. I am getting the number of
> >>> characters read,but data is not available in the buffer i used for read
> >>> call. I think it may be because of buffer is in kernel space ...I am not
> >>> sure about
> >>> that..
> >>>
> >>>
> >>> Please tell me, whats going on out there ....
> >>> Thz..
> >>>
> >>
> >>This has become a FAQ. There are some tricks that allow some file
> >>manipulation within the kernel. Others may explain. However, you
> >>seem to missing some basic information.
> >>
> >>The kernel is not a process. A file-descriptor needs a process-context
> >>for it to mean anything. Otherwise how would the kernel keep your
> >>STDIN_FILENO separate from somebody else's STDIN_FILENO?
> >>
> >>Coding a kernel module is not like coding a user-mode program. You
> >>should never write a module that requires reading or writing to any
> >>logical device. The kernel is the thing that translates physical
> >>I/O to logical I/O. Attempting to perform logical I/O in the kernel
> >>is effectively going backwards.
> >>
> >>If you need to get "outside world" information into your module, it's
> >>easy. Your module can have code for open(), read(), write(), ioctl(),
> >>and close(). A user-mode program can open() the device and perform
> >>any kind of device-specific ioctl() (or read or write or whatever)
> >>that it wants. This means that there is never, never, ever, never any
> >>real reason to attempt to perform logical (like file) I/O within the
> >>kernel at all.
> >>
> >>That said, it is possible to do file I/O in the kernel, but doing
> >>so is a severe violation of standard practice. It is also complicated
> >>and can lead to races and crashes if, for instance, a file is removed
> >>while your module has it open.
> >>
> >>You can readily code a kernel module so that it can be controlled
> >>from a user-mode script such as:
> >>
> >>insmod my-thing.o
> >>my_device < parameters
> >>
> >>Until you understand this, you should not attempt to write a kernel
> >>module.
> >>
> >>If you need human input for your module, it works the same way.
> >>
> >>Cheers,
> >>Dick Johnson
> >>
> >>Penguin : Linux version 2.3.41 on an i686 machine (800.63 BogoMips).
> >>
> >>
> >>
> >**********************
> >Praveen.M
> >Software Engineer
> >Rendezvous On Chip
> >Secunderabad.
> >Email: praveenb@trinc.com
> >**********************
>
> >
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