lib/printf.c

   1 // Implementation of cprintf console output for user environments,
   2 // based on printfmt() and the sys_cputs() system call.
   3 //
   4 // cprintf is a debugging statement, not a generic output statement.
   5 // It is very important that it always go to the console, especially when
   6 // debugging file descriptor code!
   7
   8 #include <inc/types.h>
   9 #include <inc/stdio.h>
  10 #include <inc/stdarg.h>
  11 #include <inc/lib.h>
  12
  13
  14 // Collect up to 256 characters into a buffer
  15 // and perform ONE system call to print all of them,
  16 // in order to make the lines output to the console atomic
  17 // and prevent interrupts from causing context switches
  18 // in the middle of a console output line and such.
  19 struct printbuf {
  20         int idx;        // current buffer index
  21         int cnt;        // total bytes printed so far
  22         char buf[256];
  23 };
  24
  25
  26 static void
  27 putch(int ch, struct printbuf *b)
  28 {
  29         b->buf[b->idx++] = ch;
  30         if (b->idx == 256-1) {
  31                 sys_cputs(b->buf, b->idx);
  32                 b->idx = 0;
  33         }
  34         b->cnt++;
  35 }
  36
  37 int
  38 vcprintf(const char *fmt, va_list ap)
  39 {
  40         struct printbuf b;
  41
  42         b.idx = 0;
  43         b.cnt = 0;
  44         vprintfmt((void*)putch, &b, fmt, ap);
  45         sys_cputs(b.buf, b.idx);
  46
  47         return b.cnt;
  48 }
  49
  50 int
  51 cprintf(const char *fmt, ...)
  52 {
  53         va_list ap;
  54         int cnt;
  55
  56         va_start(ap, fmt);
  57         cnt = vcprintf(fmt, ap);
  58         va_end(ap);
  59
  60         return cnt;
  61 }
  62