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Re: writing to a file in LKM

yeah, it works when i say set_fs(KERNEL_DS) before writing.


On Thu, 2 Oct 2003, Muli Ben-Yehuda wrote:

> On Thu, Oct 02, 2003 at 10:27:28AM +0200, Jan Hudec wrote:
> 
> > On Tue, Sep 30, 2003 at 13:02:42 +0530, Pradheep K E wrote:
> > > hi,
> > > i'm getting a strange problem while writing to a file from a LKM.
> > > could anyone tell me how exactly do we write to a file in the kernel mode.
> > > this code just created the file but didn't write anything to it.
> > > 
> > > struct file* f= filp_open(filename, O_CREAT|O_APPEND, 0600);
> > > f->f_op->write(f, "foo", 3, &f->fpos);
> > > filp_close(f, NULL);
> > > 
> > > the write function returned -14, and i dont know why it's giving me a 
> > > problem. is there anything more that i should do before writing to the 
> > > file?
> > 
> > You really SHOULDN'T be doing this. However, it _is_doable_.
> 
> I'd like to repeat that. If you are writing to a file fromt the
> kernel, you need to need to reevaluate the design. 
> 
> > First, look up the value 14 in errno.h -- EFAULT.
> > Hm... that suggests the buffer is not accessible. And it is NOT, because
> > it's in wrong segment. Look up the kernel_DS or some such thing. That
> > will allow copy_from_user copy from kernel address space.
> 
> The grossly misnamed get_fs() and set_fs() will come in handy
> here. Grep around to see how they are used. 
> 

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