root / lab4 / .minix-src / include / minix / endpoint.h @ 13
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1 | 13 | up20180614 | |
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2 | #ifndef _MINIX_ENDPOINT_H
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3 | #define _MINIX_ENDPOINT_H 1 |
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4 | |||
5 | #include <minix/sys_config.h> |
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6 | #include <minix/com.h> |
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7 | #include <limits.h> |
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8 | #include <minix/type.h> |
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9 | |||
10 | /*
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11 | * Endpoints are split into two parts: a process slot and a generation number.
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12 | *
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13 | * The process slot number identifies the slot in various process tables.
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14 | * It is positive or zero for user processes, and negative for kernel tasks.
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15 | * Constants dictate that with the current endpoint layout, the maximum range
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16 | * of process slot numbers is [-MAX_NR_TASKS,MAX_NR_PROCS>. The used part of
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17 | * the range is currently [-NR_TASKS,NR_PROCS> -- these two constants may be
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18 | * changed within the maximum range without changing the endpoint layout.
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19 | *
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20 | * The generation number is a per-slot number that gets increased by one every
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21 | * time a slot is reused for a new process. The generation number minimizes
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22 | * the chance that the endpoint of a dead process can (accidentially) be used
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23 | * to communicate with a different, live process. Preventing such accidents
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24 | * is essential for proper system service restartability support.
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25 | *
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26 | * The split between the two parts of the endpoint is such that when the
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27 | * generation number is zero, the endpoint number equals the process slot
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28 | * number, even for negative task numbers. This is required for the endpoint
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29 | * numbers hardcoded in <minix/com.h>, and it makes endpoint numbers easy to
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30 | * read in general.
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31 | *
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32 | * There are three special endpoint numbers: ANY, NONE, and SELF. These
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33 | * numbers are used to identify "any process", "no process at all", and
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34 | * "own process", respectively. They fall outside the normal range of
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35 | * process slot numbers, and are always of generation zero.
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36 | */
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37 | |||
38 | /*
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39 | * The following constant defines the split between the two parts of the
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40 | * endpoint numbers. It can be adjusted to allow for either more processes
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41 | * or more per-process generation numbers. Changing it will change the
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42 | * endpoint number layout, and thus break binary compatibility with existing
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43 | * processes.
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44 | */
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45 | #define _ENDPOINT_GENERATION_SHIFT 15 |
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46 | |||
47 | /* Derived constants. */
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48 | #define _ENDPOINT_GENERATION_SIZE (1 << _ENDPOINT_GENERATION_SHIFT) |
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49 | /* INT_MAX is used here to prevent signedness issues with the macros below. */
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50 | #define _ENDPOINT_MAX_GENERATION (INT_MAX/_ENDPOINT_GENERATION_SIZE-1) |
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51 | #define _ENDPOINT_SLOT_TOP (_ENDPOINT_GENERATION_SIZE-MAX_NR_TASKS)
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52 | |||
53 | /* The special endpoint numbers, and the resulting maximum slot number. */
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54 | #define ANY ((endpoint_t) (_ENDPOINT_SLOT_TOP - 1)) |
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55 | #define NONE ((endpoint_t) (_ENDPOINT_SLOT_TOP - 2)) |
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56 | #define SELF ((endpoint_t) (_ENDPOINT_SLOT_TOP - 3)) |
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57 | #define MAX_NR_PROCS (_ENDPOINT_SLOT_TOP - 3) /* (int)SELF */ |
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58 | |||
59 | /* Sanity check. */
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60 | #if NR_PROCS > MAX_NR_PROCS
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61 | #error "NR_PROCS exceeds MAX_NR_PROCS, increase _ENDPOINT_GENERATION_SHIFT" |
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62 | #endif
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63 | |||
64 | /* Generation + Process slot number <-> endpoint. */
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65 | #define _ENDPOINT(g, p) \
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66 | ((endpoint_t)(((g) << _ENDPOINT_GENERATION_SHIFT) + (p))) |
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67 | #define _ENDPOINT_G(e) (((e)+MAX_NR_TASKS) >> _ENDPOINT_GENERATION_SHIFT)
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68 | #define _ENDPOINT_P(e) \
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69 | ((((e)+MAX_NR_TASKS) & (_ENDPOINT_GENERATION_SIZE - 1)) - MAX_NR_TASKS)
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70 | |||
71 | #endif |