Re: How to get the inode - no path_lookup

[Rohan Puri <rohan.puri15@xxxxxxxxx>]

On Mon, Aug 13, 2012 at 2:17 PM, Rishi Agrawal <rishi.b.agrawal@xxxxxxxxx> wrote:

On Thu, Aug 9, 2012 at 12:39 PM, Rohan Puri <rohan.puri15@xxxxxxxxx> wrote:

On Thu, Aug 9, 2012 at 8:45 AM, Rishi Agrawal <rishi.b.agrawal@xxxxxxxxx> wrote:

On Wed, Aug 8, 2012 at 12:46 PM, Rohan Puri <rohan.puri15@xxxxxxxxx> wrote:

On Tue, Aug 7, 2012 at 8:11 PM, Rishi Agrawal <rishi.b.agrawal@xxxxxxxxx> wrote:

Hi All,


I had a module which used the path_lookup function to print the details of any file's inode. I now want to rewrite that module in order to show some juniors how to write some code in kernel.

I am using 3.4.6 kernel, I tried finding out path_lookup but google showed that it has been removed.

I tried the following code then which did not work

.
.
.
dentry = kern_path_create(AT_FDCWD, filename, &path, 1);

if (IS_ERR(dentry)) {
              printk("Failed to obtain the dentry");
               return;
       }

its not returning dentry

I again tried after seeing the implementation of vfs_stat function

user_path_at(AT_FDCWD, filename, lookup_flags, &path);

but this also fails.


I am using a proc interface to pass the filename, and copying the filename into a kernel buffer.

How can I get a copy of vfs inode for a file name.

Need to use vfs_path_lookup for this, present in fs/namei.c file, which would give you filled nameidata nd that contais inodes pointer.

--
Regards,
Rishi Agrawal


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- Rohan

vfs_path_lookup needs a dentry/mountpoint for the current path.

How will I get those.


/**
 * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
 * @dentry:  pointer to dentry of the base directory
 * @mnt: pointer to vfs mount of the base directory
 * @name: pointer to file name
 * @flags: lookup flags
 * @path: pointer to struct path to fill
 */


--
Regards,
Rishi Agrawal

If you dont have vfsmount's ptr, then you can make use of kern_path api with the LOOKUP_FOLLOW as second parameter. This will return the struct path ptr which contains vfsmount and the dentry's ptr. Now the dentry's ptr will contain the inode that you require.

- Rohan

Thanks, used that and its working now

--
Regards,
Rishi Agrawal

Good to know :)

- Rohan
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