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#ifndef _LINUX_KDEV_T_H

#define _LINUX_KDEV_T_H

#ifdef __KERNEL__

/*

As a preparation for the introduction of larger device numbers,

we introduce a type kdev_t to hold them. No information about

this type is known outside of this include file.

Objects of type kdev_t designate a device. Outside of the kernel

the corresponding things are objects of type dev_t - usually an

integral type with the device major and minor in the high and low

bits, respectively. Conversion is done by

extern kdev_t to_kdev_t(int);

It is up to the various file systems to decide how objects of type

dev_t are stored on disk.

The only other point of contact between kernel and outside world

are the system calls stat and mknod, new versions of which will

eventually have to be used in libc.

[Unfortunately, the floppy control ioctls fail to hide the internal

kernel structures, and the fd_device field of a struct floppy_drive_struct

is user-visible. So, it remains a dev_t for the moment, with some ugly

conversions in floppy.c.]

Inside the kernel, we aim for a kdev_t type that is a pointer

to a structure with information about the device (like major,

minor, size, blocksize, sectorsize, name, read-only flag,

struct file_operations etc.).

However, for the time being we let kdev_t be almost the same as dev_t:

typedef struct { unsigned short major, minor; } kdev_t;

Admissible operations on an object of type kdev_t:

- passing it along

- comparing it for equality with another such object

- storing it in ROOT_DEV, inode->i_dev, inode->i_rdev, sb->s_dev,

  bh->b_dev, req->rq_dev, de->dc_dev, tty->device

- using its bit pattern as argument in a hash function

- finding its major and minor

- complaining about it

An object of type kdev_t is created only by the function MKDEV(),

with the single exception of the constant 0 (no device).

Right now the other information mentioned above is usually found

in static arrays indexed by major or major,minor.

An obstacle to immediately using

    typedef struct { ... (* lots of information *) } *kdev_t

is the case of mknod used to create a block device that the

kernel doesn't know about at present (but first learns about

when some module is inserted).

aeb - 950811

*/

/* Since MINOR(dev) is used as index in static arrays,

   the kernel is not quite ready yet for larger minors.

   However, everything runs fine with an arbitrary kdev_t type. */

#define MINORBITS       8

#define MINORMASK       ((1<<MINORBITS) - 1)

/* SIMON I won't fuck with this one */

/*typedef unsigned short kdev_t;*/

typedef int kdev_t;

#define MAJOR(dev)      ((dev) >> MINORBITS)

#define MINOR(dev)      ((dev) & MINORMASK)

#define HASHDEV(dev)    (dev)

#define NODEV           0

#define MKDEV(ma,mi)    (((ma) << MINORBITS) | (mi))

#define B_FREE          0xffff          /* yuk */

extern char * kdevname(kdev_t); /* note: returns pointer to static data! */

/*

As long as device numbers in the outside world have 16 bits only,

we use these conversions.

*/

static inline unsigned int kdev_t_to_nr(kdev_t dev) {

        return (MAJOR(dev)<<8) | MINOR(dev);

}

static inline kdev_t to_kdev_t(int dev)

{

        int major, minor;

#if 0

        major = (dev >> 16);

        if (!major) {

                major = (dev >> 8);

                minor = (dev & 0xff);

        } else

                minor = (dev & 0xffff);

#else

        major = (dev >> 8);

        minor = (dev & 0xff);

#endif

        return MKDEV(major, minor);

}

#else /* __KERNEL__ */

/*

Some programs want their definitions of MAJOR and MINOR and MKDEV

from the kernel sources. These must be the externally visible ones.

*/

#define MAJOR(dev)      ((dev)>>8)

#define MINOR(dev)      ((dev) & 0xff)

#define MKDEV(ma,mi)    ((ma)<<8 | (mi))

#endif /* __KERNEL__ */

#endif