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Path Name to kdev_t

DISCUSSION chandrasekhar.nagaraj 7 participants 7 messages Nov 14, 2002 – Nov 15, 2002

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chandrasekhar.nagaraj

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#0 lore raw

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

#1 lore raw
Quoted 4 lines · chandrasekhar.nagaraj

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?

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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// Gianni Tedesco (gianni at ecsc dot co dot uk)
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#2 lore raw
In reply to chandrasekhar.nagaraj

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

Quoted 20 lines · chandrasekhar.nagaraj

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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#3 lore raw
In reply to chandrasekhar.nagaraj

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.

Quoted 15 lines · chandrasekhar.nagaraj

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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Please read the FAQ at http://www.tux.org/lkml/

#4 lore raw
In reply to chandrasekhar.nagaraj
Quoted 6 lines · chandrasekhar.nagaraj

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?

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;
}
#5 lore raw
Quoted 15 lines · Joe Thornber
Quoted 6 lines · chandrasekhar.nagaraj

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?

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)

Quoted 7 lines
{
	int r;
	struct nameidata nd;
	struct inode *inode;

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

missing LOOKUP_POSITIVE

Quoted 14 lines
	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;
Quoted 6 lines
	*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()

#6 lore raw
In reply to Joe Thornber
Quoted 10 lines · Joe Thornber
Quoted 6 lines · chandrasekhar.nagaraj

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?

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

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