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Kernel+Userland: Add ioctl to set process ownership of DisplayConnector

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Now that the infrastructure of the Graphics subsystem is quite stable,
it is time to try to fix a long-standing problem, which is the lack of
locking on display connector devices. Reading and writing from multiple
processes to a framebuffer controlled by the display connector is not a
huge problem - it could be solved with POSIX locking.

The real problem is some program that will try to do ioctl operations on
a display connector without the WindowServer being aware of that which
can lead to very bad situations, for example - assuming a framebuffer is
encoded at a known resolution and certain display timings, but another
process changed the ModeSetting of the display connector, leading to
inconsistency on the properties of the current ModeSetting.

To solve this, there's a new "master" ioctl to take "ownership" and
another one to release that ownership of a display connector device. To
ensure we will not hold a Process object forever just because it has an
ownership over a display connector, we hold it with a weak reference,
and if the process is gone, someone else can take an ownership.
This commit is contained in:
Liav A 2022-06-10 14:16:28 +03:00 • committed by Linus Groh
parent 1968aba69b
commit 977aa81310
5 changed files with 101 additions and 8 deletions
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20
Userland/Services/WindowServer/main.cpp
View file

@ -9,6 +9,7 @@
#include "EventLoop.h"
#include "Screen.h"
#include "WindowManager.h"
#include <Kernel/API/Graphics.h>
#include <LibCore/ConfigFile.h>
#include <LibCore/DirIterator.h>
#include <LibCore/File.h>
@ -68,7 +69,7 @@ ErrorOr<int> serenity_main(Main::Arguments)
WindowServer::ScreenLayout screen_layout;
String error_msg;
auto add_unconfigured_display_connector_devices = [&]() {
auto add_unconfigured_display_connector_devices = [&]() -> ErrorOr<void> {
// Enumerate the /dev/gpu/connectorX devices and try to set up any ones we find that we haven't already used
Core::DirIterator di("/dev/gpu", Core::DirIterator::SkipParentAndBaseDir);
while (di.has_next()) {
@ -78,18 +79,23 @@ ErrorOr<int> serenity_main(Main::Arguments)
auto full_path = String::formatted("/dev/gpu/{}", path);
if (!Core::File::is_device(full_path))
continue;
auto display_connector_fd = TRY(Core::System::open(full_path, O_RDWR | O_CLOEXEC));
if (int rc = graphics_connector_set_responsible(display_connector_fd); rc != 0)
return Error::from_syscall("graphics_connector_set_responsible"sv, rc);
TRY(Core::System::close(display_connector_fd));
if (fb_devices_configured.find(full_path) != fb_devices_configured.end())
continue;
if (!screen_layout.try_auto_add_display_connector(full_path))
dbgln("Could not auto-add display connector device {} to screen layout", full_path);
}
return {};
};
auto apply_and_generate_generic_screen_layout = [&]() {
auto apply_and_generate_generic_screen_layout = [&]() -> ErrorOr<bool> {
screen_layout = {};
fb_devices_configured = {};
add_unconfigured_display_connector_devices();
TRY(add_unconfigured_display_connector_devices());
if (!WindowServer::Screen::apply_layout(move(screen_layout), error_msg)) {
dbgln("Failed to apply generated fallback screen layout: {}", error_msg);
return false;
@ -104,17 +110,15 @@ ErrorOr<int> serenity_main(Main::Arguments)
if (screen_info.mode == WindowServer::ScreenLayout::Screen::Mode::Device)
fb_devices_configured.set(screen_info.device.value());
add_unconfigured_display_connector_devices();
TRY(add_unconfigured_display_connector_devices());
if (!WindowServer::Screen::apply_layout(move(screen_layout), error_msg)) {
dbgln("Error applying screen layout: {}", error_msg);
if (!apply_and_generate_generic_screen_layout())
return 1;
TRY(apply_and_generate_generic_screen_layout());
}
} else {
dbgln("Error loading screen configuration: {}", error_msg);
if (!apply_and_generate_generic_screen_layout())
return 1;
TRY(apply_and_generate_generic_screen_layout());
}
}