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Core Wayland window system code and protocol
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Demi Marie Obenour adf84614ca connection: Do not busy-loop if a message exceeds the buffer size 
If the length of a message exceeds the maximum length of the buffer, the
buffer size will reach its maximum value and stay there forever, with no
message ever being successfully processed.  Since libwayland uses
level-triggered epoll, this will cause the compositor to loop forever
and consume CPU time.  In libwayland 1.22 and below, there was an
explicit check that caused messages exceeding 4096 bytes to result in an
EOVERFLOW error, preventing the loop.  However, this check was removed
between d074d52902 ("connection: Dynamically resize connection buffers").

To prevent this problem, always limit the size of messages to 4096 bytes.
Since the default and minimum buffer size is 4096 bytes, this ensures
that a single message will always fit in the buffer.  It would be
possible to allow larger messages if the buffer size was larger, but the
maximum size of a message should not depend on the buffer size chosen by
the compositor.

Rejecting messages that exceed 4092 bytes seems to have the advantage of
reserving 4 bits, not 3, in the size field for future use.  However,
message sizes in the range [0x0, 0x7] are invalid, so one can obtain a
fourth bit by negating the meaning of bit 12 if bits 0 through 11
(inclusive) are 0.  Allowing 4096-byte messages provides the far more
important advantage that regressions compared to 1.22 are impossible
and regressions compared to 1.23 are extremely unlikely.  The only case
where a regression is possible is:

- The receiving side is using libwayland 1.23.
- The sending side is either using libwayland 1.23 or is not using
  libwayland.
- The sender sends a message exceeding 4096 bytes.
- If the sender of the large message is the client, the server has
  increased the buffer size from the default value.

This combination is considered extremely unlikely, as libwayland 1.22
and below would disconnect upon receiving such a large message.
4096-byte messages, however, have always worked, so there was no reason
to avoid sending them.

Fixes: d074d52902 ("connection: Dynamically resize connection buffers").
Fixes: #494
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
2025-06-21 11:29:04 +00:00
.gitlab/issue_templates gitlab: make issue template the default 2023-11-21 15:44:31 +00:00
cursor cursor: Properly check realloc for errors 2025-06-08 16:16:09 +00:00
doc doc: add a section on color management 2025-06-12 14:37:32 +03:00
egl egl: Make wayland-egl symbols check depend on wayland_egl 2025-06-08 17:30:55 +00:00
protocol protocol: drop reference to linux-explicit-synchronization 2025-05-20 20:57:52 +00:00
src connection: Do not busy-loop if a message exceeds the buffer size 2025-06-21 11:29:04 +00:00
tests tests: Depend on exec-fd-leak-checker 2025-06-08 17:30:55 +00:00
.editorconfig editorconfig: add settings for the .gitlab-ci.yml file 2020-06-05 08:22:34 +10:00
.gitignore build: drop autotools 2021-03-05 09:15:04 +00:00
.gitlab-ci.yml ci: Update ci-templates 2025-01-21 16:43:45 +00:00
.mailmap Add a .mailmap file 2023-03-25 11:17:32 -05:00
.triage-policies.yml Add a triage-policies file for bugbot 2023-07-07 21:18:08 +10:00
CONTRIBUTING.md CONTRIBUTING: fix typo "excercising" 2020-12-17 16:03:14 -05:00
COPYING COPYING: Update to MIT Expat License rather than MIT X License 2015-06-12 15:31:21 -07:00
meson.build build: bump version to 1.23.90 for the RC1 release 2025-05-22 21:00:30 +02:00
meson_options.txt meson: Use proper type for bools 2022-04-02 17:04:08 +03:00
README.md readme: convert to Markdown 2023-02-13 19:57:15 +01:00
release.sh release.sh: Don't push *all* tags 2023-01-16 10:03:54 +00:00
releasing.txt Add release.sh 2022-07-14 08:04:43 +00:00
wayland-scanner.m4 build: check wayland-scanner version 2020-01-16 17:25:06 +01:00
wayland-scanner.mk Pass input/output files as arguments to wayland-scanner 2017-08-18 15:20:24 +03:00

README.md

Wayland

Wayland is a project to define a protocol for a compositor to talk to its clients as well as a library implementation of the protocol. The compositor can be a standalone display server running on Linux kernel modesetting and evdev input devices, an X application, or a wayland client itself. The clients can be traditional applications, X servers (rootless or fullscreen) or other display servers.

The wayland protocol is essentially only about input handling and buffer management. The compositor receives input events and forwards them to the relevant client. The clients creates buffers and renders into them and notifies the compositor when it needs to redraw. The protocol also handles drag and drop, selections, window management and other interactions that must go through the compositor. However, the protocol does not handle rendering, which is one of the features that makes wayland so simple. All clients are expected to handle rendering themselves, typically through cairo or OpenGL.

Building the wayland libraries is fairly simple, aside from libffi, they don't have many dependencies:

$ git clone https://gitlab.freedesktop.org/wayland/wayland
$ cd wayland
$ meson build/ --prefix=PREFIX
$ ninja -C build/ install

where PREFIX is where you want to install the libraries.

See https://wayland.freedesktop.org for documentation.