include/linux/kdev

/* */
This source file includes following definitions.
kdev_t_to_nr
to_kdev_t
   1 #ifndef _LINUX_KDEV_T_H
   2 #define _LINUX_KDEV_T_H
   3 #ifdef __KERNEL__
   4 /*
   5 As a preparation for the introduction of larger device numbers,
   6 we introduce a type kdev_t to hold them. No information about
   7 this type is known outside of this include file.
   8 
   9 Objects of type kdev_t designate a device. Outside of the kernel
  10 the corresponding things are objects of type dev_t - usually an
  11 integral type with the device major and minor in the high and low
  12 bits, respectively. Conversion is done by
  13 
  14 extern kdev_t to_kdev_t(int);
  15 
  16 It is up to the various file systems to decide how objects of type
  17 dev_t are stored on disk.
  18 The only other point of contact between kernel and outside world
  19 are the system calls stat and mknod, new versions of which will
  20 eventually have to be used in libc.
  21 
  22 [Unfortunately, the floppy control ioctls fail to hide the internal
  23 kernel structures, and the fd_device field of a struct floppy_drive_struct
  24 is user-visible. So, it remains a dev_t for the moment, with some ugly
  25 conversions in floppy.c.]
  26 
  27 Inside the kernel, we aim for a kdev_t type that is a pointer
  28 to a structure with information about the device (like major,
  29 minor, size, blocksize, sectorsize, name, read-only flag,
  30 struct file_operations etc.).
  31 
  32 However, for the time being we let kdev_t be almost the same as dev_t:
  33 
  34 typedef struct { unsigned short major, minor; } kdev_t;
  35 
  36 Admissible operations on an object of type kdev_t:
  37 - passing it along
  38 - comparing it for equality with another such object
  39 - storing it in ROOT_DEV, inode->i_dev, inode->i_rdev, sb->s_dev,
  40   bh->b_dev, req->rq_dev, de->dc_dev, tty->device
  41 - using its bit pattern as argument in a hash function
  42 - finding its major and minor
  43 - complaining about it
  44 
  45 An object of type kdev_t is created only by the function MKDEV(),
  46 with the single exception of the constant 0 (no device).
  47 
  48 Right now the other information mentioned above is usually found
  49 in static arrays indexed by major or major,minor.
  50 
  51 An obstacle to immediately using
  52     typedef struct { ... (* lots of information *) } *kdev_t
  53 is the case of mknod used to create a block device that the
  54 kernel doesn't know about at present (but first learns about
  55 when some module is inserted).
  56 
  57 aeb - 950811
  58 */
  59 
  60 /* Since MINOR(dev) is used as index in static arrays,
  61    the kernel is not quite ready yet for larger minors.
  62    However, everything runs fine with an arbitrary kdev_t type. */
  63 
  64 #define MINORBITS       8
  65 #define MINORMASK       ((1<<MINORBITS) - 1)
  66 
  67 typedef unsigned short kdev_t;
  68 
  69 #define MAJOR(dev)      ((dev) >> MINORBITS)
  70 #define MINOR(dev)      ((dev) & MINORMASK)
  71 #define HASHDEV(dev)    (dev)
  72 #define NODEV           0
  73 #define MKDEV(ma,mi)    (((ma) << MINORBITS) | (mi))
  74 #define B_FREE          0xffff          /* yuk */
  75 
  76 extern char * kdevname(kdev_t); /* note: returns pointer to static data! */
  77 
  78 /*
  79 As long as device numbers in the outside world have 16 bits only,
  80 we use these conversions.
  81 */
  82 
  83 static inline unsigned int kdev_t_to_nr(kdev_t dev) {
     /*  */
  84         return (MAJOR(dev)<<8) | MINOR(dev);
  85 }
  86 
  87 static inline kdev_t to_kdev_t(int dev)
     /*  */
  88 {
  89         int major, minor;
  90 #if 0
  91         major = (dev >> 16);
  92         if (!major) {
  93                 major = (dev >> 8);
  94                 minor = (dev & 0xff);
  95         } else
  96                 minor = (dev & 0xffff);
  97 #else
  98         major = (dev >> 8);
  99         minor = (dev & 0xff);
 100 #endif
 101         return MKDEV(major, minor);
 102 }
 103 
 104 #else /* __KERNEL__ */
 105 
 106 /*
 107 Some programs want their definitions of MAJOR and MINOR and MKDEV
 108 from the kernel sources. These must be the externally visible ones.
 109 */
 110 #define MAJOR(dev)      ((dev)>>8)
 111 #define MINOR(dev)      ((dev) & 0xff)
 112 #define MKDEV(ma,mi)    ((ma)<<8 | (mi))
 113 #endif /* __KERNEL__ */
 114 #endif
/* */
root/include/linux/kdev_t.h

INCLUDED FROM

DEFINITIONS
