minix/servers/devman/buf.c

   1 /* buf.c - by Alen Stojanov and David van Moolenbroek, taken from procfs */
   2
   3 #include "devman.h"
   4 #include "proto.h"
   5 #include <stdarg.h>
   6 #include <assert.h>
   7
   8 static char *buf;
   9 static size_t left, used;
  10 static off_t skip;
  11
  12 /*===========================================================================*
  13  *                              buf_init                                     *
  14  *===========================================================================*/
  15 void buf_init(char *ptr, size_t len, off_t start)
  16 {
  17         /* Initialize the buffer for fresh use. The output is to be stored into
  18          * 'ptr' which is BUF_SIZE bytes in size, since that is the size we
  19          * requested. Due to the way vsnprintf works, we cannot use the last
  20          * byte of this buffer. The first 'start' bytes of the produced output
  21          * are to be skipped. After that, a total of 'len' bytes are requested.
  22          */
  23
  24         buf = ptr;
  25         skip = start;
  26         left = MIN(len, BUF_SIZE - 1);
  27         used = 0;
  28 }
  29
  30 /*===========================================================================*
  31  *                              buf_printf                                   *
  32  *===========================================================================*/
  33 void buf_printf(char *fmt, ...)
  34 {
  35         /* Add formatted text to the end of the buffer.
  36          */
  37         va_list args;
  38         ssize_t len, max;
  39
  40         if (left == 0)
  41                 return;
  42
  43         /* There is no way to estimate how much space the result will take, so
  44          * we need to produce the string even when skipping part of the start.
  45          * The null terminating character is not part of the result, so room
  46          * must be given for it to be stored after completely filling up the
  47          * requested part of the buffer.
  48          */
  49         max = MIN(skip + left + 1, BUF_SIZE);
  50
  51         va_start(args, fmt);
  52         len = vsnprintf(&buf[used], max, fmt, args);
  53         va_end(args);
  54
  55         /* The snprintf family returns the number of bytes that would be stored
  56          * if the buffer were large enough, excluding the null terminator.
  57          */
  58         if (len >= BUF_SIZE)
  59                 len = BUF_SIZE - 1;
  60
  61         if (skip > 0) {
  62                 assert(used == 0);
  63
  64                 if (skip >= len) {
  65                         skip -= len;
  66
  67                         return;
  68                 }
  69
  70                 memmove(buf, &buf[skip], len - skip);
  71
  72                 len -= skip;
  73                 skip = 0;
  74         }
  75
  76         assert(skip == 0);
  77         assert(len >= 0);
  78         assert((ssize_t) left >= 0);
  79
  80         if (len > (ssize_t) left)
  81                 len = left;
  82
  83         used += len;
  84         left -= len;
  85 }
  86
  87 /*===========================================================================*
  88  *                              buf_append                                   *
  89  *===========================================================================*/
  90 void buf_append(char *data, size_t len)
  91 {
  92         /* Add arbitrary data to the end of the buffer.
  93          */
  94
  95         if (left == 0)
  96                 return;
  97
  98         if (skip > 0) {
  99                 if (skip >= (ssize_t) len) {
 100                         skip -= len;
 101
 102                         return;
 103                 }
 104
 105                 data += skip;
 106                 len -= skip;
 107                 skip = 0;
 108         }
 109
 110         if (len > left)
 111                 len = left;
 112
 113         memcpy(&buf[used], data, len);
 114
 115         used += len;
 116         left -= len;
 117 }
 118
 119 /*===========================================================================*
 120  *                              buf_result                                   *
 121  *===========================================================================*/
 122 ssize_t buf_result(void)
 123 {
 124         /* Return the resulting number of bytes produced, not counting the
 125          * trailing null character in the buffer.
 126          */
 127
 128         return used;
 129 }