arch/m68k/include/asm/shm.h

   1 #ifndef _M68K_SHM_H
   2 #define _M68K_SHM_H
   3
   4
   5 /* format of page table entries that correspond to shared memory pages
   6    currently out in swap space (see also mm/swap.c):
   7    bits 0-1 (PAGE_PRESENT) is  = 0
   8    bits 8..2 (SWP_TYPE) are = SHM_SWP_TYPE
   9    bits 31..9 are used like this:
  10    bits 15..9 (SHM_ID) the id of the shared memory segment
  11    bits 30..16 (SHM_IDX) the index of the page within the shared memory segment
  12                     (actually only bits 25..16 get used since SHMMAX is so low)
  13    bit 31 (SHM_READ_ONLY) flag whether the page belongs to a read-only attach
  14 */
  15 /* on the m68k both bits 0 and 1 must be zero */
  16 /* format on the sun3 is similar, but bits 30, 31 are set to zero and all
  17    others are reduced by 2. --m */
  18
  19 #ifndef CONFIG_SUN3
  20 #define SHM_ID_SHIFT    9
  21 #else
  22 #define SHM_ID_SHIFT    7
  23 #endif
  24 #define _SHM_ID_BITS    7
  25 #define SHM_ID_MASK     ((1<<_SHM_ID_BITS)-1)
  26
  27 #define SHM_IDX_SHIFT   (SHM_ID_SHIFT+_SHM_ID_BITS)
  28 #define _SHM_IDX_BITS   15
  29 #define SHM_IDX_MASK    ((1<<_SHM_IDX_BITS)-1)
  30
  31 #endif /* _M68K_SHM_H */