servers/devman/buf.c

   1 /* buf.c - by Alen Stojanov and David van Moolenbroek, taken from procfs */
   2 #define _POSIX_SOURCE      1    /* tell headers to include POSIX stuff */
   3 #define _MINIX             1    /* tell headers to include MINIX stuff */
   4 #define _SYSTEM            1    /* tell headers that this is the kernel */
   5 #define DEVMAN_SERVER      1
   6
   7 #include <minix/config.h>
   8 #include <errno.h>
   9 #include <unistd.h>
  10 #include <stdlib.h>
  11 #include <stdio.h>
  12 #include <string.h>
  13 #include <lib.h>
  14 #include <timers.h>
  15
  16 #include <minix/callnr.h>
  17 #include <minix/type.h>
  18 #include <minix/const.h>
  19 #include <minix/com.h>
  20 #include <minix/syslib.h>
  21 #include <minix/sysutil.h>
  22 #include <minix/vfsif.h>
  23 #include <minix/endpoint.h>
  24 #include <minix/sysinfo.h>
  25 #include <minix/u64.h>
  26 #include <minix/sysinfo.h>
  27 #include <minix/type.h>
  28 #include <minix/ipc.h>
  29
  30 #include <sys/time.h>
  31 #include <sys/times.h>
  32 #include <sys/types.h>
  33 #include <sys/stat.h>
  34
  35 #include <minix/vtreefs.h>
  36
  37 #include <minix/devman.h>
  38
  39
  40 #include <stdarg.h>
  41 #include <assert.h>
  42 #include <string.h>
  43 #define BUF_SIZE 4096
  44
  45 static char buf[BUF_SIZE + 1];
  46 static size_t off, left, used;
  47 static off_t skip;
  48
  49 /*===========================================================================*
  50  *                              buf_init                                     *
  51  *===========================================================================*/
  52 void buf_init(off_t start, size_t len)
  53 {
  54         /* Initialize the buffer for fresh use. The first 'start' bytes of the
  55          * produced output are to be skipped. After that, up to a total of
  56          * 'len' bytes are requested.
  57          */
  58
  59         skip = start;
  60         left = MIN(len, BUF_SIZE);
  61         off = 0;
  62         used = 0;
  63 }
  64
  65 /*===========================================================================*
  66  *                              buf_printf                                   *
  67  *===========================================================================*/
  68 void buf_printf(char *fmt, ...)
  69 {
  70         /* Add formatted text to the end of the buffer.
  71          */
  72         va_list args;
  73         ssize_t len, max;
  74
  75         if (left == 0)
  76                 return;
  77
  78         /* There is no way to estimate how much space the result will take, so
  79          * we need to produce the string even when skipping part of the start.
  80          * If part of the result is to be skipped, do not memcpy; instead, save
  81          * the offset of where the result starts within the buffer.
  82          *
  83          * The null terminating character is not part of the result, so room
  84          * must be given for it to be stored after completely filling up the
  85          * requested part of the buffer.
  86          */
  87         max = MIN(skip + left, BUF_SIZE);
  88
  89         va_start(args, fmt);
  90         len = vsnprintf(&buf[off + used], max + 1, fmt, args);
  91         va_end(args);
  92
  93         if (skip > 0) {
  94                 assert(off == 0);
  95                 assert(used == 0);
  96
  97                 if (skip >= len) {
  98                         skip -= len;
  99
 100                         return;
 101                 }
 102
 103                 off = skip;
 104                 if (left > BUF_SIZE - off)
 105                         left = BUF_SIZE - off;
 106                 len -= off;
 107                 skip = 0;
 108         }
 109
 110         assert(skip == 0);
 111         assert(len >= 0);
 112         assert((long) left >= 0);
 113
 114         if (len > (ssize_t) left)
 115                 len = left;
 116
 117         used += len;
 118         left -= len;
 119 }
 120
 121 /*===========================================================================*
 122  *                              buf_append                                   *
 123  *===========================================================================*/
 124 void buf_append(char *data, size_t len)
 125 {
 126         /* Add arbitrary data to the end of the buffer.
 127          */
 128
 129         if (left == 0)
 130                 return;
 131
 132         if (skip > 0) {
 133                 if (skip >= (ssize_t) len) {
 134                         skip -= len;
 135
 136                         return;
 137                 }
 138
 139                 data += skip;
 140                 len -= skip;
 141                 skip = 0;
 142         }
 143
 144         if (len > left)
 145                 len = left;
 146
 147         memcpy(&buf[off + used], data, len);
 148
 149         used += len;
 150         left -= len;
 151 }
 152
 153 /*===========================================================================*
 154  *                              buf_get                                      *
 155  *===========================================================================*/
 156 size_t buf_get(char **ptr)
 157 {
 158         /* Return the buffer's starting address and the length of the used
 159          * part, not counting the trailing null character for the latter.
 160          */
 161
 162         *ptr = &buf[off];
 163
 164         return used;
 165 }