jos/lib/printf.c

63 lines
1.2 KiB
C
Raw Normal View History

2018-09-25 09:22:51 -07:00
// Implementation of cprintf console output for user environments,
// based on printfmt() and the sys_cputs() system call.
//
// cprintf is a debugging statement, not a generic output statement.
// It is very important that it always go to the console, especially when
// debugging file descriptor code!
#include <inc/types.h>
#include <inc/stdio.h>
#include <inc/stdarg.h>
#include <inc/lib.h>
// Collect up to 256 characters into a buffer
// and perform ONE system call to print all of them,
// in order to make the lines output to the console atomic
// and prevent interrupts from causing context switches
// in the middle of a console output line and such.
struct printbuf {
int idx; // current buffer index
int cnt; // total bytes printed so far
char buf[256];
};
static void
putch(int ch, struct printbuf *b)
{
b->buf[b->idx++] = ch;
if (b->idx == 256-1) {
sys_cputs(b->buf, b->idx);
b->idx = 0;
}
b->cnt++;
}
int
vcprintf(const char *fmt, va_list ap)
{
struct printbuf b;
b.idx = 0;
b.cnt = 0;
vprintfmt((void*)putch, &b, fmt, ap);
sys_cputs(b.buf, b.idx);
return b.cnt;
}
int
cprintf(const char *fmt, ...)
{
va_list ap;
int cnt;
va_start(ap, fmt);
cnt = vcprintf(fmt, ap);
va_end(ap);
return cnt;
}