process-util: turn off O_NONBLOCK on stdio fds when rearranging fds

We often create our fds O_NONBLOCK, but when we want to invoke some
program with them as stdin/stdout/stderr we really should turn it off
again.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/basic/fd-util.c b/src/basic/fd-util.c
index 1a279690d2..38866ebb78 100644
--- a/src/basic/fd-util.c
+++ b/src/basic/fd-util.c
@@ -170,6 +170,19 @@ int fd_nonblock(int fd, bool nonblock) {
         return RET_NERRNO(fcntl(fd, F_SETFL, nflags));
 }
 
+int stdio_disable_nonblock(void) {
+        int ret = 0;
+
+        /* stdin/stdout/stderr really should have O_NONBLOCK, which would confuse apps if left on, as
+         * write()s might unexpectedly fail with EAGAIN. */
+
+        RET_GATHER(ret, fd_nonblock(STDIN_FILENO, false));
+        RET_GATHER(ret, fd_nonblock(STDOUT_FILENO, false));
+        RET_GATHER(ret, fd_nonblock(STDERR_FILENO, false));
+
+        return ret;
+}
+
 int fd_cloexec(int fd, bool cloexec) {
         int flags, nflags;