Very Computer

Hi,

In one of the part of my driver module , I have a path name to a device file
(for eg:- /dev/hda1) .Now if I want to obtain the associated major number
and minor number i.e. device ID(kdev_t) of this file what would be the
procedure?

Thanks and Regards
Chandrasekhar

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You need to lookup the inode from the path using namei() or something
then it's just a field in the inode.

Check out fs/namei.c and related headers for more details.

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You would want to find a struct file * that represents the device (look
at fs/open.c in the sys_open calls, it shows how to convert a filename
to a file *) then look at file->f_dentry->d_inode->i_bdev->bd_dev.  This
is the major/minor dev_t for the device.

Hope this helps.
Thanks
-steve

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in all functions of the driver where you will need the kdev_t (e.g.: the VFS
layer hooks) you will receive either a struct inode* and/or the struct file*
of the device file. the i_rdev member of struct inode is defined as the
kdev_t of the particular device.

hope this helps.

regards,
irfan.

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I think this should be standard function, I'm sure lots of people are
duplicating this code.  For 2.4 kernels:

/*
 * Convert a device path to a kdev_t.
 */
static int lookup_device(const char *path, kdev_t *dev)
{
        int r;
        struct nameidata nd;
        struct inode *inode;

        if (!path_init(path, LOOKUP_FOLLOW, &nd))
                return 0;

        if ((r = path_walk(path, &nd)))
                goto out;

        inode = nd.dentry->d_inode;
        if (!inode) {
                r = -ENOENT;
                goto out;
        }

        if (!S_ISBLK(inode->i_mode)) {
                r = -EINVAL;
                goto out;
        }

        *dev = inode->i_rdev;

 out:
        path_release(&nd);
        return r;

Quote:}

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missing LOOKUP_POSITIVE

Quote:

>    if ((r = path_walk(path, &nd)))
>            goto out;

>    inode = nd.dentry->d_inode;
>    if (!inode) {
>            r = -ENOENT;
>            goto out;
>    }

>    if (!S_ISBLK(inode->i_mode)) {
>            r = -EINVAL;
>            goto out;
>    }

shouldb be -ENOTBLK

new check here:

        if (nd.mnt->mnt_flags & MNT_NODEV)
                r = -EACCES;

Quote:

>    *dev = inode->i_rdev;

>  out:
>    path_release(&nd);
>    return r;

I also think that this doesn not make much sense, you really want
name to properly opened struct block_device * instead, i.e. the firsdt halve
of get_sb_bdev()

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No, it really shouldn't.  You should _NOT_ mess with kdev_t - use real
objects instead.

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