minix3/include/minix/endpoint.h

76 lines
3.1 KiB
C

#ifndef _MINIX_ENDPOINT_H
#define _MINIX_ENDPOINT_H 1
#ifdef _MINIX_SYSTEM
#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 /* _MINIX_SYSTEM */
#endif