Make pread async in case fd is valid but not what we are looking for

1 files changed, 25 insertions, 2 deletions

diff --git a/runfd.c b/runfd.c
index 50eea7f..59b9d8c 100644
--- a/runfd.c
+++ b/runfd.c
@@ -14,6 +14,24 @@
 
 char *args[] = { "batchrun", NULL };
 
+void
+set_async(int fd, int on)
+{
+	int flags;
+
+	if ((flags = fcntl(fd, F_GETFL)) == -1)
+		err(1, "fcntl()");
+
+	if (on) {
+		flags |= O_NONBLOCK;
+	} else {
+		flags &= ~O_NONBLOCK;
+	}
+
+	if (fcntl(fd, F_SETFL, flags) == -1)
+		err(1, "fcntl()");
+}
+
 int
 main(int argc, char **argv)
 {
@@ -28,6 +46,8 @@ main(int argc, char **argv)
 			errx(1, "Filedescriptor supplied (\"%s\") is not a number", argv[1]);
 	}
 
+	set_async(fd, 1);
+
 retry:
 	if (tries++ >= 3)
 		errx(1, "Failed to read file header");
@@ -35,16 +55,19 @@ retry:
 	ret = pread(fd, buf, sizeof(buf), 0);
 	if (ret == 2) {
 		if (strncmp(buf, "#!", 2) != 0) {
-			fcntl(3, F_SETFD, FD_CLOEXEC);
+			fcntl(fd, F_SETFD, FD_CLOEXEC);
 		}
 	} else if (ret == -1) {
 		if (errno == EINTR)
 			goto retry;
-		err(1, "pread()");
+		else if (errno != EAGAIN)
+			err(1, "pread()");
 	} else if (ret != 0) {
 		goto retry;
 	}
 
+	set_async(fd, 0);
+
 	fexecve(fd, args, NULL);
 	err(1, "fexecve()");
 }