lib/fprintf.c

   1 #include <inc/lib.h>
   2
   3 // Collect up to 256 characters into a buffer
   4 // and perform ONE system call to print all of them,
   5 // in order to make the lines output to the console atomic
   6 // and prevent interrupts from causing context switches
   7 // in the middle of a console output line and such.
   8 struct printbuf {
   9         int fd;         // file descriptor
  10         int idx;        // current buffer index
  11         ssize_t result; // accumulated results from write
  12         int error;      // first error that occurred
  13         char buf[256];
  14 };
  15
  16
  17 static void
  18 writebuf(struct printbuf *b)
  19 {
  20         if (b->error > 0) {
  21                 ssize_t result = write(b->fd, b->buf, b->idx);
  22                 if (result > 0)
  23                         b->result += result;
  24                 if (result != b->idx) // error, or wrote less than supplied
  25                         b->error = (result < 0 ? result : 0);
  26         }
  27 }
  28
  29 static void
  30 putch(int ch, void *thunk)
  31 {
  32         struct printbuf *b = (struct printbuf *) thunk;
  33         b->buf[b->idx++] = ch;
  34         if (b->idx == 256) {
  35                 writebuf(b);
  36                 b->idx = 0;
  37         }
  38 }
  39
  40 int
  41 vfprintf(int fd, const char *fmt, va_list ap)
  42 {
  43         struct printbuf b;
  44
  45         b.fd = fd;
  46         b.idx = 0;
  47         b.result = 0;
  48         b.error = 1;
  49         vprintfmt(putch, &b, fmt, ap);
  50         if (b.idx > 0)
  51                 writebuf(&b);
  52
  53         return (b.result ? b.result : b.error);
  54 }
  55
  56 int
  57 fprintf(int fd, const char *fmt, ...)
  58 {
  59         va_list ap;
  60         int cnt;
  61
  62         va_start(ap, fmt);
  63         cnt = vfprintf(fd, fmt, ap);
  64         va_end(ap);
  65
  66         return cnt;
  67 }
  68
  69 int
  70 printf(const char *fmt, ...)
  71 {
  72         va_list ap;
  73         int cnt;
  74
  75         va_start(ap, fmt);
  76         cnt = vfprintf(1, fmt, ap);
  77         va_end(ap);
  78
  79         return cnt;
  80 }
  81