linux-kernel - Re: create a file in kernel mode. help please!

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Date:	Wed, 23 Jan 2008 19:02:08 +0100
From:	Jan Kara <jack@...e.cz>
To:	Rafael Sisto <rafael.sisto@...il.com>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: create a file in kernel mode. help please!

  Hi,

> obviously this is a newbie question, but I couldn't find any
> documentation on how to do it.. I tried several ways but couldnt do
> it.
> I designed a system call, so a user will call it, and a new file will
> be created ('/tmp/filexx'). After that, I have another system call,
> that will map the file into the maps of the user process. The idea is
> the same as IPC...
> 
> I managed to create the file with this function (in the first system call):
>         fd = filp_open(path, O_CREAT | O_RDWR , 777);
> 
> After that, the user will call another system call, and it will map
> this file to the process maps.
> something like this:
>          filp_open(route, O_RDWR,0 );
>          do_mmap(fp, 0, tamano, PROT_READ | PROT_WRITE | PROT_EXEC,
> MAP_SHARED, 0);
> 
> After I call the second system call, the user tries to access the
> memory, but gets the message "Bus Error".
> I tried to manually create a file with vi, and then use the second
> system call, and worked perfectly. I could use the shared memory
> without problems.
> 
> The problems seems to be in the first system call (with filp_open),
> when I try to create a new file... Can somebody suggest me something,
> on how I could fix this issue?? It is very important because it is for
> a college projects.
  Hmm, I don't quite get what you are trying to achieve? Why can't user
create the file via open(path, O_CREAT...) and then mmap() it? Why do
you need a new system call for that?

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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