SDL: Don't use udev for joystick enumeration if running in a container

From 8d43f45a7b7ceab6a7d1aa8bf8afa905853ba8c2 Mon Sep 17 00:00:00 2001
From: Ludovico de Nittis <[EMAIL REDACTED]>
Date: Tue, 16 Feb 2021 14:13:30 +0100
Subject: [PATCH] Don't use udev for joystick enumeration if running in a
 container

If we are running in a container, like Flatpak[1] or pressure-vessel[2],
it's likely that we are using user namespaces,
therefore udev event notification via netlink won't work reliably.
Use their filesystem API to detect them and automatically fallback to
the inotify-based enumeration.

[1] <https://flatpak.org/>
[2]
<https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/tree/master/pressure-vessel>

Signed-off-by: Ludovico de Nittis <ludovico.denittis@collabora.com>
---
 src/joystick/hidapi/SDL_hidapijoystick.c | 8 ++++++++
 src/joystick/linux/SDL_sysjoystick.c     | 5 ++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/joystick/hidapi/SDL_hidapijoystick.c b/src/joystick/hidapi/SDL_hidapijoystick.c
index 25eb7b6dc..899da9ee2 100644
--- a/src/joystick/hidapi/SDL_hidapijoystick.c
+++ b/src/joystick/hidapi/SDL_hidapijoystick.c
@@ -740,6 +740,14 @@ HIDAPI_JoystickInit(void)
             SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
                          "udev disabled by SDL_HIDAPI_JOYSTICK_DISABLE_UDEV");
             linux_enumeration_method = ENUMERATION_FALLBACK;
+        } else if (access("/.flatpak-info", F_OK) == 0
+                   || access("/run/host/container-manager", F_OK) == 0) {
+            /* Explicitly check `/.flatpak-info` because, for old versions of
+             * Flatpak, this was the only available way to tell if we were in
+             * a Flatpak container. */
+            SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
+                         "Container detected, disabling HIDAPI udev integration");
+            linux_enumeration_method = ENUMERATION_FALLBACK;
         } else {
             SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
                          "Using udev for HIDAPI joystick device discovery");
diff --git a/src/joystick/linux/SDL_sysjoystick.c b/src/joystick/linux/SDL_sysjoystick.c
index 5b013019b..466cee6da 100644
--- a/src/joystick/linux/SDL_sysjoystick.c
+++ b/src/joystick/linux/SDL_sysjoystick.c
@@ -658,7 +658,10 @@ LINUX_JoystickInit(void)
             enumeration_method = ENUMERATION_FALLBACK;
         }
         else if (access("/.flatpak-info", F_OK) == 0
-                 || access("/run/pressure-vessel", F_OK) == 0) {
+                 || access("/run/host/container-manager", F_OK) == 0) {
+            /* Explicitly check `/.flatpak-info` because, for old versions of
+             * Flatpak, this was the only available way to tell if we were in
+             * a Flatpak container. */
             SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
                          "Container detected, disabling udev integration");
             enumeration_method = ENUMERATION_FALLBACK;