LCOM1920-T02G10

#ifndef _MINIX_ENDPOINT_H

#define _MINIX_ENDPOINT_H 1

#include <minix/sys_config.h>

#include <minix/com.h>

#include <limits.h>

#include <minix/type.h>

/*

 * Endpoints are split into two parts: a process slot and a generation number.

 *

 * The process slot number identifies the slot in various process tables.

 * It is positive or zero for user processes, and negative for kernel tasks.

 * Constants dictate that with the current endpoint layout, the maximum range

 * of process slot numbers is [-MAX_NR_TASKS,MAX_NR_PROCS>.  The used part of

 * the range is currently [-NR_TASKS,NR_PROCS> -- these two constants may be

 * changed within the maximum range without changing the endpoint layout.

 *

 * The generation number is a per-slot number that gets increased by one every

 * time a slot is reused for a new process.  The generation number minimizes

 * the chance that the endpoint of a dead process can (accidentially) be used

 * to communicate with a different, live process.  Preventing such accidents

 * is essential for proper system service restartability support.

 *

 * The split between the two parts of the endpoint is such that when the

 * generation number is zero, the endpoint number equals the process slot

 * number, even for negative task numbers.  This is required for the endpoint

 * numbers hardcoded in <minix/com.h>, and it makes endpoint numbers easy to

 * read in general.

 *

 * There are three special endpoint numbers: ANY, NONE, and SELF.  These

 * numbers are used to identify "any process", "no process at all", and

 * "own process", respectively.  They fall outside the normal range of

 * process slot numbers, and are always of generation zero.

 */

/*

 * The following constant defines the split between the two parts of the

 * endpoint numbers.  It can be adjusted to allow for either more processes

 * or more per-process generation numbers.  Changing it will change the

 * endpoint number layout, and thus break binary compatibility with existing

 * processes.

 */

#define _ENDPOINT_GENERATION_SHIFT        15

/* Derived constants. */

#define _ENDPOINT_GENERATION_SIZE        (1 << _ENDPOINT_GENERATION_SHIFT)

/* INT_MAX is used here to prevent signedness issues with the macros below. */

#define _ENDPOINT_MAX_GENERATION        (INT_MAX/_ENDPOINT_GENERATION_SIZE-1)

#define _ENDPOINT_SLOT_TOP        (_ENDPOINT_GENERATION_SIZE-MAX_NR_TASKS)

/* The special endpoint numbers, and the resulting maximum slot number. */

#define ANY                ((endpoint_t) (_ENDPOINT_SLOT_TOP - 1))

#define NONE                ((endpoint_t) (_ENDPOINT_SLOT_TOP - 2))

#define SELF                ((endpoint_t) (_ENDPOINT_SLOT_TOP - 3))

#define MAX_NR_PROCS                      (_ENDPOINT_SLOT_TOP - 3)        /* (int)SELF */

/* Sanity check. */

#if NR_PROCS > MAX_NR_PROCS

#error "NR_PROCS exceeds MAX_NR_PROCS, increase _ENDPOINT_GENERATION_SHIFT"

#endif

/* Generation + Process slot number <-> endpoint. */

#define _ENDPOINT(g, p) \

        ((endpoint_t)(((g) << _ENDPOINT_GENERATION_SHIFT) + (p)))

#define _ENDPOINT_G(e) (((e)+MAX_NR_TASKS) >> _ENDPOINT_GENERATION_SHIFT)

#define _ENDPOINT_P(e) \

        ((((e)+MAX_NR_TASKS) & (_ENDPOINT_GENERATION_SIZE - 1)) - MAX_NR_TASKS)

#endif