Re: set_fs

[amith <amith@xxxxxxxxxxxxxxx>]

Brad Dickerson wrote:

> Hello,
>   I am trying to call the open function from within a kernel module.
> After searching the web, I tried the following snippet:
>  mm_segment_t old_fs;
>  old_fs=get_fs();
>  set_fs(USER_DS);
>  fp=open('/etc/config.txt',O_RDONLY);
>  getLine(fp,line);
>  close(fp);
>  set_fs(old_fs);
> For some reason, the open fails and returns -1. Any ideas on what I am 
> doing wrong? This is all really new to me.
> thanks,
> Brad 

hi there,
                  please modify it for your use .

kopen (const char *filename, int flags)  /* user defined function for 
opening a file from within  kernel space  */
{
 oldmm = get_fs ();
 set_fs (get_ds ());
 kfd = sys_open (filename, flags | O_CREAT, S_IRWXU);   /* create one 
if one doesnt exist */
 set_fs (oldmm);
 return kfd;
}

note that you would have get and set again if you want to read/write to 
the file .


/* returns number of bytes read or corresponding error code
*  in case of failure
*  see the man pages for more "man 2 read" 
*/

int
kread (int fd, char *buffer, int size)
{
 int red;

 oldmm = get_fs ();
 set_fs (get_ds ());
 red = sys_read (fd, buffer, size);
 set_fs (oldmm);
 return red;
}

/*  returns number of bytes written or corresponding error code
*  in case of failure
*  see the man pages for more "man 2 write" 
*/


int
kwrite (int fd, char *buffer, int size)
{
 int red;

 oldmm = get_fs ();
 set_fs (get_ds ());
 red = sys_write (fd, buffer, size);
 set_fs (oldmm);
 return red;
}

hope this helps  .
cheers,
Amith.



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