stderr has been redirected to /dev/null so all logging needs to go to
syslog.

This change adds support for the VMware Mouse Position
pseudo-encoding[1], which is used to notify VNC clients when X11 clients
call `XWarpPointer()`[2]. This function is called by SDL (and other
similar libraries)  when they detect that the server does not support
native relative motion, like some RFB clients.

With this, RFB clients can choose to adjust the local cursor position
under certain circumstances to match what the server has set. For
instance, if pointer lock has been enabled on the client's machine and
the cursor is not being drawn locally, the local position of the cursor
is irrelevant, so the RFB client can use what the server sends as the
canonical absolute position of the cursor. This ultimately enables the
possibility of games (especially FPS games) to behave how users expect
(if the clients implement the corresponding change).

Part of: #619

1: https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#vmware-cursor-position-pseudo-encoding
2: https://tronche.com/gui/x/xlib/input/XWarpPointer.html
3: https://hg.libsdl.org/SDL/file/28e3b60e2131/src/events/SDL_mouse.c#l804

Otherwise we might end up owners of something we cannot deliver data on,
which can hang applications.

Setting `rfbport` to `-1` disables TCP port listening.

This is what display managers do, so it is expected by many
environments.

We terminated the child instead of the parent after fork().

Reported by Jan Grulich from Red Hat.

Mainly fixes for Japanese and Korean keyboard layouts.

It is now dynamically generated, so it will be in the build directory
and not in the source directory.

This is needed by vncserver which doesn't know which parameters are
boolean, and it cannot use the -Param=Value form as that isn't tolerated
by the Xorg code.

Refer @CMAKE_INSTALL_FULL_SYSCONF@ instead.

Not sure why this got in there, but it is incorrect as it results in
creating files with too liberal permissions.

This line affects every command run by the user, unlike everything else
in our policy which is just for vncserver/vncsession. It's easy to miss
this so add a comment pointing it out.

Allow vnc session labeled with SELinux vnc_session_t domain to create
directory in user homedir ~/.vnc labeled with SELinux label xdm_home_t.

Because also process vncpasswd creates ~/.vnc directory, file transition that
userdomain attribute SELinux domain (label for the process) can create the
directory with the same label needs to be added.

userdomain attribute contains following SELinux types:
    auditadm_t
    dbadm_t
    guest_t
    logadm_t
    secadm_t
    staff_t
    staff_wine_t
    sysadm_t
    unconfined_t
    user_t
    user_wine_t
    webadm_t
    xguest_t

Signed-off-by: Lukas Vrabec <lvrabec@redhat.com>

If the X server is not shut down cleanly, it can leave UNIX domain
sockets around that "vncserver" has previously mis-identified as
evidence that the display number is still in use.

Instead of checking for existence of /tmp/.X11-unix/X<n>, the code
will now attempt to connect to the socket to confirm that there is a
server process listening on this UNIX domain socket. This will
eliminate false positives in the case the UNIX domain socket still
exists but is not associated with a listening Xorg server. The Xorg
server does not have a problem with fixing this file when it next
starts up. It is only important to avoid using the port if it is still
in use.

The display check and related setup code was complex due to
compatibility with Perl 4. This included different ways of obtaining
system constants and building system data structures. Perl 5 provides
direct constants and utility methods to abstract this out of the
vncserver code.

If the X server is not shut down cleanly, it may leave lock files
around that "vncserver" has previously mis-identified as evidence that
the display number is still in use.

Instead of checking for existence of /tmp/.X<n>-lock, the code will
now extract the PID from the lock file and confirm that a process
exists with the same PID. This will eliminate false positives in the
case that this file references a PID that no longer exists. The Xorg
server does not have a problem with fixing this file when it next
starts up. It is only important to avoid using the port if it is still
in use.

The display check had duplicate code to first check if the X11 port is
not in use, and then check that the RFB port is not in use. Eliminate
the duplicate code by using a for-loop.

Several calculated values such as file paths and port numbers were
hard coded within strings or expressions, sometimes multiple
times. These values should be extracted into named variables to
improve self-documentation and avoid accidental divergence.

Checking for the existence of `/tmp/.X<n>-lock` is a fast read-only
operation, while calls to bind() or connect() are more expensive and
may have side effects. Perform the fast operation first.

The check for existence of `/usr/spool/sockets/X11/<n>` has been
removed. This file is only relevant on HP-UX, and TigerVNC dropped
support for HP-UX in commit 31e5aa3.

It's quite easy to make a mistake and add an additional space when configuring
users in the vncserver.users config file. You will then get an error that the
user doesn't exist and it's hard to spot the mistake. Same applies for a space
before the display number.

It expects the callers to include this, so make sure we're consistently
providing one.

Major restructuring of how streams work. Neither input nor output
streams are now blocking. This avoids stalling the rest of the client or
server when a peer is slow or unresponsive.

Note that this puts an extra burden on users of streams to make sure
they are allowed to do their work once the underlying transports are
ready (e.g. monitoring fds).

External callers don't need to know the exact details, only if there is
data that needs to be flushed or not.

Might as well make these explicit so the cost is apparent.

vncsession-start is running in SELinux vnc_session_t domain because of
"SELinuxContext=system_u:system_r:vnc_session_t:s0" option in systemd
vncserver@.service unit file. vncsession-start executing binary
vncsession with SELinux label/type vnc_session_t. This access was not
allowed in vncsession policy.

This is the current upstream so let's make use of it to get the latest
in features and fixes.

It creates an invalid region if given an empty rect. Fortunately
RegionInitBoxes() handles that just fine, so use that instead.

We no longer support such old X servers so start using the current
functions.

It seems like many of the X11 operations can end up with no pixels
actually changing. So instead of discovering and adding workarounds for
each individually we'll just check very region added if it's empty.

We now require at least 1.16, so remove all code that handled older
versions than that.

We removed support in the code ages ago, but overlooked this part of the
documentation. Also remove some dead code in Xvnc on the same theme.

No current distribution ship anything this ancient anyway.

This makes our builds directly compatible with most distributions
without packagers/users having to specify extra flags.

Running as a service on a SELinux system requires rules so we can
transition to our own context. We also need the proper permissions
to start new user sessions.

This sets up a more correct session as there are key tasks that
need to be performed by PAM. E.g. systemd will allocate cgroups
and start base services.

In order to easily handle this as a system service the mapping of
displays is now done via a configuration file.

Assume we are part of a complete and proper installation and encode the
full expected path in to the vncserver script.

It keeps much better track of the X server and startup files than
we can do.

We need to be started as a system service for things to work correctly
anyway, so delegate the work of starting and stopping things to the
system service manager (e.g. systemd).

This is how display managers (e.g. gdm or lightdm) start sessions
and is necessary to get the proper set of environment variables.

We don't want to create files in the users home directory unless we
have to. Users can read about how this file works in our man pages.

We now have config files for more fine grained control of these
things, so avoid duplicating the functionality.

These might contain values we want if we are start from a proper
environment.