Kernel file access example.....

chxooi · 05-11-2010, 02:13 AM

This example code is file access(read) into the kernel level..
There is "/tmp/rambo.txt"...

and open() is ok...

but, this function is not work...
I can see the error message...<data is NULL> return -14...
# pwd
/tmp
# ls -la
drwxrwxrwt 4 root 0 140 Jan 2 05:04 .
drwxrwxrwx 23 500 501 4096 May 11 2010 ..
-rwxrwxrwx 1 root 0 40 Jan 2 05:04 rambo.txt
#
# cat rambo.txt
abcdefgzjdkzdwdadasdoda90d12334afdaafaf
#

Code:

EXAMPLE CODE.....


    struct file * fd;
    char * filename="/tmp/rambo.txt";
    char *buff=NULL;
    printk("read function...\n");
    fd=sfile_open(filename,O_RDONLY,0);
    if (fd != NULL) {
        printk("OK.....\n");
        count=10;
        offset=0;
        sfile_read(fd,offset,buff,count);
        printk(" buff %s\n",buff);
    }else{
        printk("not ok\n");
    }

After example excutition
=============
read function...
OK.....
file_read...=
data is <NULL>,ret is -14

====================
What is the reason of "data is <NULL>".
Return is -14 is also problem...

Code:

#if 1
struct file* sfile_open(const char* path, int flags, int rights) {
    struct file* filp = NULL;
    mm_segment_t oldfs;
    int err = 0;
 
    oldfs = get_fs();
    set_fs(get_ds());
    filp = filp_open(path, flags, rights);
    set_fs(oldfs);
    if(IS_ERR(filp)) {
        err = PTR_ERR(filp);
        return NULL;
    }
    return filp;
}
void file_close(struct file* file) {
    filp_close(file, NULL);
}
 
int sfile_read(struct file* file, unsigned long long offset, unsigned char* data, unsigned int size) {
    mm_segment_t oldfs;
    int ret;
 
    printk("file_read...=\n");
    oldfs = get_fs();
    set_fs(get_ds());
 
    ret = vfs_read(file, data, size, &offset);
    printk("data is %s,ret is %d\n",data,ret);
 
    set_fs(oldfs);
    return ret;
}