use a local temp buffer for unbuffered streams in vfprintf

this change makes it so most calls to fprintf(stderr, ...) will result
in a single writev syscall, as opposed to roughly 2*N syscalls (and
possibly more) where N is the number of format specifiers. in
principle we could use a much larger buffer, but it's best not to
increase the stack requirements too much. most messages are under 80
chars.

diff --git a/src/stdio/stderr.c b/src/stdio/stderr.c
index 3bdaffb..9a70700 100644 (file)
--- a/src/stdio/stderr.c
+++ b/src/stdio/stderr.c
@@ -6,6 +6,7 @@ static FILE f = {
        .buf_size = 0,
        .fd = 2,
        .flags = F_PERM | F_NORD,
+       .lbf = -1,
        .write = __stdio_write,
        .seek = __stdio_seek,
        .close = __stdio_close,

diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index 57878c0..8cbfd96 100644 (file)
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -627,13 +627,26 @@ int vfprintf(FILE *f, const char *fmt, va_list ap)
        va_list ap2;
        int nl_type[NL_ARGMAX] = {0};
        union arg nl_arg[NL_ARGMAX];
+       unsigned char internal_buf[80], *saved_buf = 0;
        int ret;
 
        va_copy(ap2, ap);
        if (printf_core(0, fmt, &ap2, nl_arg, nl_type) < 0) return -1;
 
        FLOCK(f);
+       if (!f->buf_size) {
+               saved_buf = f->buf;
+               f->buf = internal_buf;
+               f->buf_size = sizeof internal_buf;
+       }
        ret = printf_core(f, fmt, &ap2, nl_arg, nl_type);
+       if (saved_buf) {
+               f->write(f, 0, 0);
+               if (!f->wpos) ret = -1;
+               f->buf = saved_buf;
+               f->buf_size = 0;
+               f->wpos = f->wbase = f->wend = 0;
+       }
        FUNLOCK(f);
        va_end(ap2);
        return ret;