From: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
Create a gentle version of `unix_stream_listen()`. This version does
not call `die()` if a socket-fd cannot be created and does not assume
that it is safe to `unlink()` an existing socket-inode.
`unix_stream_listen()` uses `unix_stream_socket()` helper function to
create the socket-fd. Avoid that helper because it calls `die()` on
errors.
`unix_stream_listen()` always tries to `unlink()` the socket-path before
calling `bind()`. If there is an existing server/daemon already bound
and listening on that socket-path, our `unlink()` would have the effect
of disassociating the existing server's bound-socket-fd from the socket-path
without notifying the existing server. The existing server could continue
to service existing connections (accepted-socket-fd's), but would not
receive any futher new connections (since clients rendezvous via the
socket-path). The existing server would effectively be offline but yet
appear to be active.
Furthermore, `unix_stream_listen()` creates an opportunity for a brief
race condition for connecting clients if they try to connect in the
interval between the forced `unlink()` and the subsequent `bind()` (which
recreates the socket-path that is bound to a new socket-fd in the current
process).
Signed-off-by: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
---
unix-socket.c | 39 +++++++++++++++++++++++++++++++++++++++
unix-socket.h | 8 ++++++++
2 files changed, 47 insertions(+)
diff --git a/unix-socket.c b/unix-socket.c
index 19ed48be990..3a9ffc32268 100644
--- a/unix-socket.c
+++ b/unix-socket.c
@@ -121,3 +121,42 @@ int unix_stream_listen(const char *path)
errno = saved_errno;
return -1;
}
+
+int unix_stream_listen_gently(const char *path,
+ const struct unix_stream_listen_opts *opts)
+{
+ int fd = -1;
+ int bind_successful = 0;
+ int saved_errno;
+ struct sockaddr_un sa;
+ struct unix_sockaddr_context ctx;
+
+ if (unix_sockaddr_init(&sa, path, &ctx) < 0)
+ goto fail;
+
+ fd = socket(AF_UNIX, SOCK_STREAM, 0);
+ if (fd < 0)
+ goto fail;
+
+ if (opts->force_unlink_before_bind)
+ unlink(path);
+
+ if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0)
+ goto fail;
+ bind_successful = 1;
+
+ if (listen(fd, opts->listen_backlog_size) < 0)
+ goto fail;
+
+ unix_sockaddr_cleanup(&ctx);
+ return fd;
+
+fail:
+ saved_errno = errno;
+ unix_sockaddr_cleanup(&ctx);
+ close(fd);
+ if (bind_successful)
+ unlink(path);
+ errno = saved_errno;
+ return -1;
+}
diff --git a/unix-socket.h b/unix-socket.h
index e271aeec5a0..253f579f087 100644
--- a/unix-socket.h
+++ b/unix-socket.h
@@ -4,4 +4,12 @@
int unix_stream_connect(const char *path);
int unix_stream_listen(const char *path);
+struct unix_stream_listen_opts {
+ int listen_backlog_size;
+ unsigned int force_unlink_before_bind:1;
+};
+
+int unix_stream_listen_gently(const char *path,
+ const struct unix_stream_listen_opts *opts);
+
#endif /* UNIX_SOCKET_H */
--
gitgitgadget
