how to get inode of the file in the kernel

Hi,

is there a way for a kernel module to get an inode of the file
specified by the full path?


thanks,
Jiri Olsa
--
To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.linux-learn.org/faqs

Re: how to get inode of the file in the kernel

On Mon, Apr 28, 2008 at 9:10 PM, Jiri Olsa wrote:
> Hi,
>
> is there a way for a kernel module to get an inode of the file
> specified by the full path?
>

check this function in fs/file_table.c - noticed how given the file
structure, u can get the inode information:

/**
* drop_file_write_access - give up ability to write to a file
* @file: the file to which we will stop writing
*
* This is a central place which will give up the ability
* to write to @file, along with access to write through
* its vfsmount.
*/
void drop_file_write_access(struct file *file)
{
struct vfsmount *mnt = file->f_path.mnt;
struct dentry *dentry = file->f_path.dentry;
struct inode *inode = dentry->d_inode;

put_write_access(inode);

if (special_file(inode->i_mode))
return;
if (file_check_writeable(file) != 0)
return;
mnt_drop_write(mnt);
file_release_write(file);
}

Next, opening by filename open() is through do_sys_open():

long do_sys_open(int dfd, const char __user *filename, int flags, int mode)
{
char *tmp = getname(filename);
int fd = PTR_ERR(tmp);

if (!IS_ERR(tmp)) {
fd = get_unused_fd_flags(flags);
if (fd >= 0) {
struct file *f = do_filp_open(dfd, tmp, flags, mode);
if (IS_ERR(f)) {
put_unused_fd(fd);
fd = PTR_ERR(f);
} else {
fsnotify_open(f->f_path.dentry);
fd_install(fd, f);
}
}
putname(tmp);
}
return fd;
}

And from above, do_filp_open() will return the struct file structure,
within which u can find inode information as shown above.

On the other hand, why not download e2fsprogs from sourceforge:

check this function in lib/ext2fs/namei.c:

static errcode_t open_namei(ext2_filsys fs, ext2_ino_t root, ext2_ino_t base,
const char *pathname, size_t pathlen, int follow,
int link_count, char *buf, ext2_ino_t *res_inode)
{
const char *base_name;
int namelen;
ext2_ino_t dir, inode;
errcode_t retval;

#ifdef NAMEI_DEBUG
printf("open_namei: root=%lu, dir=%lu, path=%*s, lc=%d\n",
root, base, pathlen, pathname, link_count);
#endif
retval = dir_namei(fs, root, base, pathname, pathlen,
link_count, buf, &base_name, &namelen, &dir);
if (retval) return retval;
if (!namelen) { /* special case: '/usr/' etc */
*res_inode=dir;
return 0;
}
retval = ext2fs_lookup (fs, dir, base_name, namelen, buf, &inode);
if (retval)
return retval;
if (follow) {
retval = follow_link(fs, root, dir, inode, link_count,
buf, &inode);

u can see how the filename, come in and update the inode structre,
done inside ext2fs_lookup().

--
Regards,
Peter Teoh
--
To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.linux-learn.org/faqs