This was a requested feature. To make sure that FEXServer is running and
managed by a parent process, we need to have a way to tell FEXServer to
keep alive without any FEX clients. The best way to do this is to pass
FEXServer a Pipe (like FEX does when a client starts it), but instead of
FEXServer signaling to FEXInterpreter that it's ready. FEXServer listens
to the pipe to see if the management process is still alive.
The expectation here is that the management process passes FEXServer the
read end of a pipe, and when the management software is done (or gets
killed by the kernel!) then the write end of the pipe is closed, and
FEXServer naturally closes (As long as there's no FEX processes
remaining).
The problem here is that the pipe we used for telling FEXInterpreter
that the FEXServer is ready to accept connections was inherited by
erofsfuse or squashfuse. So the closing of the pipe from the FEXServer
side would leave a reference open in squashfuse or erofsfuse.
Fix this by setting FD_CLOEXEC on the pipe, but also pass the pipe FD
through an argument instead of scanning for all pipes.
Then once we execve the squashfuse/erofsfuse application, the FD isn't
inherited.
Fixes#4329
It can be useful to know in tooling when the current active FEXServer
has exited.
Two things can happen when this command is run.
No FEXServer is active, returns immediately.
A FEXServer is active, we query for a pidfd from the active server, then
we wait until it exits.
Both instances of this is valid to use.
This is a relatively invasive change since multiple things needed to
happen at once.
* Socket based logging is removed
* Logging has been replaced to only support stdout, stderr, and server
* Server is now default and replaces what FEXLogServer did
* Server logging now uses a pipe instead of a socket
* Can be faster than stderr and stdout since the application doesn't
need to wait on terminal output
* FEXMountDaemon has been removed
* Functionality has been merged in to FEXServer
* FEXServer is always executed on FEX initialization time
* Similar in behaviour to Wine's wineserver
* Can explicitly start this before using FEX for logging purposes
* Stays around until all instances of FEX exit
* Will stick around for a short amount of time in case of spurious
execution
* FEXServer will soon be extended to do more than logging and squashfs
mounting
* FEX rootfs scripts will need to be updated to support this path
* Just means rbinding the /tmp folder and forcing a FEXServer instance
to be alive
* Pressure-vessel works fine in this case since FEXServer will already
be running
* It already rbinds the host /tmp folder which is why this works
Ryan Houdek