---------- Forwarded message ----------
From: Brandon Niemczyk <bniemczyk@xxxxxxxxx>
Date: Wed, 6 Oct 2004 02:28:09 -0400
Subject: Re: How to read from kernel ?
To: Danett song <danett18@xxxxxxxxxxxx>
Why do you want to read a file from a kernel module?
I would think it would be better to implement something in proc,
sysctl, or something.
On Tue, 5 Oct 2004 20:02:07 -0300 (ART), Danett song
<danett18@xxxxxxxxxxxx> wrote:
> Hello,
>
> I tryed figure out how to read a file from a LKM, i
> done like this:
>
> At init_module
>
> int init_module(void){
>
> or_open=sys_call_table[__NR_open];
> or_read=sys_call_table[__NR_read];
> or_close=sys_call_table[__NR_close];
>
> return(0);
> }
>
> So the code in a function that need to read a file:
>
> char tmp[512];
> char buff[1024];
> int ret, size;
> mm_segment_t old_fs;
>
> memset(tmp, 0, sizeof(tmp));
>
> strcpy(tmp, "/tmp/myfile.txt");
>
> //old_fs = get_fs();
> //set_fs(get_ds());
>
> ret = (*or_open) (tmp, O_RDONLY|O_LARGEFILE, 0640);
>
> //set_fs(old_fs);
>
> if ( ret < 0){
>
> printk("\nFailed to open");
> return (0);
>
> }
>
> memset(buff, 0, sizeof(buff));
>
> size = (*or_read)(ret, buff, sizeof(buff));
>
> printk("\nContents is %s", buff);
>
> (*or_close)(ret);
>
> Well, the problem is if i don't use get_fs() and
> set_fs() i always get value ZERO from open! :(
>
> If i use get_fs() and set_fs() then my kernel crash.
> What i'm doing wrong ? Can someone give me a example ?
>
> Someone can say that i shouldn't use the read, open,
> etc from syscall_table... but i only found this
> example in internet, if someone present-me a better
> way i will use.
>
> Regards,
>
>
> _______________________________________________________
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> --
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>
>
--
Brandon Niemczyk
http://bniemczyk.doesntexist.com
--
Brandon Niemczyk
http://bniemczyk.doesntexist.com
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
