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 #define MIN(x,y) (x<y?x:y)
  50
  51 /*===========================================================================*
  52  *                              buf_init                                     *
  53  *===========================================================================*/
  54 void buf_init(off_t start, size_t len)
  55 {
  56         /* Initialize the buffer for fresh use. The first 'start' bytes of the
  57          * produced output are to be skipped. After that, up to a total of
  58          * 'len' bytes are requested.
  59          */
  60
  61         skip = start;
  62         left = MIN(len, BUF_SIZE);
  63         off = 0;
  64         used = 0;
  65 }
  66
  67 /*===========================================================================*
  68  *                              buf_printf                                   *
  69  *===========================================================================*/
  70 void buf_printf(char *fmt, ...)
  71 {
  72         /* Add formatted text to the end of the buffer.
  73          */
  74         va_list args;
  75         ssize_t len, max;
  76
  77         if (left == 0)
  78                 return;
  79
  80         /* There is no way to estimate how much space the result will take, so
  81          * we need to produce the string even when skipping part of the start.
  82          * If part of the result is to be skipped, do not memcpy; instead, save
  83          * the offset of where the result starts within the buffer.
  84          *
  85          * The null terminating character is not part of the result, so room
  86          * must be given for it to be stored after completely filling up the
  87          * requested part of the buffer.
  88          */
  89         max = MIN(skip + left, BUF_SIZE);
  90
  91         va_start(args, fmt);
  92         len = vsnprintf(&buf[off + used], max + 1, fmt, args);
  93         va_end(args);
  94
  95         if (skip > 0) {
  96                 assert(off == 0);
  97                 assert(used == 0);
  98
  99                 if (skip >= len) {
 100                         skip -= len;
 101
 102                         return;
 103                 }
 104
 105                 off = skip;
 106                 if (left > BUF_SIZE - off)
 107                         left = BUF_SIZE - off;
 108                 len -= off;
 109                 skip = 0;
 110         }
 111
 112         assert(skip == 0);
 113         assert(len >= 0);
 114         assert((long) left >= 0);
 115
 116         if (len > (ssize_t) left)
 117                 len = left;
 118
 119         used += len;
 120         left -= len;
 121 }
 122
 123 /*===========================================================================*
 124  *                              buf_append                                   *
 125  *===========================================================================*/
 126 void buf_append(char *data, size_t len)
 127 {
 128         /* Add arbitrary data to the end of the buffer.
 129          */
 130
 131         if (left == 0)
 132                 return;
 133
 134         if (skip > 0) {
 135                 if (skip >= (ssize_t) len) {
 136                         skip -= len;
 137
 138                         return;
 139                 }
 140
 141                 data += skip;
 142                 len -= skip;
 143                 skip = 0;
 144         }
 145
 146         if (len > left)
 147                 len = left;
 148
 149         memcpy(&buf[off + used], data, len);
 150
 151         used += len;
 152         left -= len;
 153 }
 154
 155 /*===========================================================================*
 156  *                              buf_get                                      *
 157  *===========================================================================*/
 158 size_t buf_get(char **ptr)
 159 {
 160         /* Return the buffer's starting address and the length of the used
 161          * part, not counting the trailing null character for the latter.
 162          */
 163
 164         *ptr = &buf[off];
 165
 166         return used;
 167 }