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 72