include/minix/endpoint.h

   1
   2 #ifndef _MINIX_ENDPOINT_H
   3 #define _MINIX_ENDPOINT_H 1
   4
   5 #include <minix/sys_config.h>
   6 #include <minix/com.h>
   7 #include <limits.h>
   8 #include <minix/type.h>
   9
  10 /*
  11  * Endpoints are split into two parts: a process slot and a generation number.
  12  *
  13  * The process slot number identifies the slot in various process tables.
  14  * It is positive or zero for user processes, and negative for kernel tasks.
  15  * Constants dictate that with the current endpoint layout, the maximum range
  16  * of process slot numbers is [-MAX_NR_TASKS,MAX_NR_PROCS>.  The used part of
  17  * the range is currently [-NR_TASKS,NR_PROCS> -- these two constants may be
  18  * changed within the maximum range without changing the endpoint layout.
  19  *
  20  * The generation number is a per-slot number that gets increased by one every
  21  * time a slot is reused for a new process.  The generation number minimizes
  22  * the chance that the endpoint of a dead process can (accidentially) be used
  23  * to communicate with a different, live process.  Preventing such accidents
  24  * is essential for proper system service restartability support.
  25  *
  26  * The split between the two parts of the endpoint is such that when the
  27  * generation number is zero, the endpoint number equals the process slot
  28  * number, even for negative task numbers.  This is required for the endpoint
  29  * numbers hardcoded in <minix/com.h>, and it makes endpoint numbers easy to
  30  * read in general.
  31  *
  32  * There are three special endpoint numbers: ANY, NONE, and SELF.  These
  33  * numbers are used to identify "any process", "no process at all", and
  34  * "own process", respectively.  They fall outside the normal range of
  35  * process slot numbers, and are always of generation zero.
  36  */
  37
  38 /*
  39  * The following constant defines the split between the two parts of the
  40  * endpoint numbers.  It can be adjusted to allow for either more processes
  41  * or more per-process generation numbers.  Changing it will change the
  42  * endpoint number layout, and thus break binary compatibility with existing
  43  * processes.
  44  */
  45 #define _ENDPOINT_GENERATION_SHIFT      15
  46
  47 /* Derived constants. */
  48 #define _ENDPOINT_GENERATION_SIZE       (1 << _ENDPOINT_GENERATION_SHIFT)
  49 /* INT_MAX is used here to prevent signedness issues with the macros below. */
  50 #define _ENDPOINT_MAX_GENERATION        (INT_MAX/_ENDPOINT_GENERATION_SIZE-1)
  51 #define _ENDPOINT_SLOT_TOP      (_ENDPOINT_GENERATION_SIZE-MAX_NR_TASKS)
  52
  53 /* The special endpoint numbers, and the resulting maximum slot number. */
  54 #define ANY             ((endpoint_t) (_ENDPOINT_SLOT_TOP - 1))
  55 #define NONE            ((endpoint_t) (_ENDPOINT_SLOT_TOP - 2))
  56 #define SELF            ((endpoint_t) (_ENDPOINT_SLOT_TOP - 3))
  57 #define MAX_NR_PROCS                  (_ENDPOINT_SLOT_TOP - 3)  /* (int)SELF */
  58
  59 /* Sanity check. */
  60 #if NR_PROCS > MAX_NR_PROCS
  61 #error "NR_PROCS exceeds MAX_NR_PROCS, increase _ENDPOINT_GENERATION_SHIFT"
  62 #endif
  63
  64 /* Generation + Process slot number <-> endpoint. */
  65 #define _ENDPOINT(g, p) \
  66         ((endpoint_t)(((g) << _ENDPOINT_GENERATION_SHIFT) + (p)))
  67 #define _ENDPOINT_G(e) (((e)+MAX_NR_TASKS) >> _ENDPOINT_GENERATION_SHIFT)
  68 #define _ENDPOINT_P(e) \
  69         ((((e)+MAX_NR_TASKS) & (_ENDPOINT_GENERATION_SIZE - 1)) - MAX_NR_TASKS)
  70
  71 #endif