1 files changed, 154 insertions, 0 deletions
diff --git a/yes.c b/yes.c
new file mode 100644
index 0000000..2da0ec5
--- /dev/null
+++ b/yes.c
@@ -0,0 +1,154 @@
+/* See LICENSE file for copyright and license details. */
+
+#define _GNU_SOURCE
+#include <sys/ioctl.h>
+#include <sys/uio.h>
+#include <alloca.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+
+#ifndef CAPACITY
+# define CAPACITY (1 << 20)
+#endif
+
+
+static char *argv0;
+static void (*writeall)(char *, size_t);
+
+
+static void
+writeall_write(char *buf, size_t n)
+{
+	ssize_t r;
+	for (; n; n -= (size_t)r, buf += r)
+		if ((r = write(STDOUT_FILENO, buf, n)) < 0)
+			perror(argv0), exit(1);
+}
+
+#if 0
+static void
+writeall_vmsplice(char *buf, size_t n)
+{
+	struct iovec iov;
+	ssize_t r;
+	iov.iov_base = buf;
+	iov.iov_len = n;
+	while (iov.iov_len) {
+		r = vmsplice(STDOUT_FILENO, &iov, 1, 0);
+		if (r < 0) {
+			if (errno == EINVAL) {
+				writeall = writeall_write;
+				writeall_write(iov.iov_base, iov.iov_len);
+				return;
+			}
+			perror(argv0), exit(1);
+		}
+		iov.iov_base += r;
+		iov.iov_len -= (size_t)r;
+	}
+}
+#endif
+
+int
+main(int argc, char *argv[])
+{
+	size_t n, len, m = 0, p, cap = 0;
+	char *buf, *b;
+	int i, sz, fds[2], flags;
+	ssize_t r;
+
+	if (!argc)
+		argc = 1;
+	argv0 = argv[0] ? argv[0] : "yes";
+	if (argc == 1) {
+		argc = 2;
+		argv = (char *[]){argv0, "y"};
+	}
+	n = (size_t)(argc - 1);
+
+	writeall = writeall_write;
+
+	for (i = 1; i < argc; i++)
+		n += strlen(argv[i]);
+	b = buf = alloca(n);
+	for (i = 1; i < argc; i++) {
+		b = stpcpy(b, argv[i]);
+		*b++ = ' ';
+	}
+	b[-1] = '\n';
+
+	if (pipe(fds))
+		goto fail;
+
+	if (fds[0] == STDOUT_FILENO || fds[1] == STDOUT_FILENO) {
+		errno = EBADF;
+		goto fail;
+	}
+
+	if ((flags = fcntl(fds[1], F_GETFL)) == -1)
+		goto fail;
+	if (fcntl(fds[1], F_SETFL, flags | O_NONBLOCK) == -1)
+		goto fail;
+
+	if ((sz = fcntl(STDOUT_FILENO, F_GETPIPE_SZ)) > 0) {
+		if (sz < CAPACITY)
+			if (fcntl(STDOUT_FILENO, F_SETPIPE_SZ, CAPACITY) != -1)
+				sz = CAPACITY;
+		fcntl(fds[1], F_SETPIPE_SZ, sz);
+	} else {
+		fcntl(fds[1], F_SETPIPE_SZ, 3 << 16);
+	}
+
+	for (b = buf, p = n;;) {
+		r = write(fds[1], b, p);
+		if (r < 0) {
+			if (errno == EAGAIN)
+				break;
+			goto fail;
+		}
+		b += r;
+		cap += (size_t)r;
+		p -= (size_t)r;
+		if (!p) {
+			b = buf;
+			p = n;
+			m += 1;
+		}
+	}
+
+	cap -= cap % n;
+	len = n;
+	n *= m;
+	if (m)
+		cap = n;
+
+	for (;;) {
+		r = tee(fds[0], STDOUT_FILENO, cap, 0);
+		if (r < (ssize_t)n) {
+			if (r < 0) {
+				if (errno == EINVAL)
+					goto fallback;
+				goto fail;
+			}
+			r %= len;
+			writeall(buf + r, len - r);
+		}
+	}
+
+fallback:
+	for (p = 0;; p = (p + (size_t)r) % len) {
+		if ((r = write(STDOUT_FILENO, buf + p, len - p)) < 0)
+			goto fail;
+	}
+
+	return 0;
+
+fail:
+	perror(argv0);
+	return 1;
+}