Fixes#2136
This is a fairly tricky edge case to support with FEX.
If execveat is used with AT_EMPTY_PATH then the application can pass an
FD to execve instead of a filename. This includes FDs that have been
deleted from the disk so the child process can't open it by filename
anymore.
To work around this limitation, we need to pass the FD to the new FEX
process and open it directly, similar to how binfmt_misc works with FDs.
The FD will get passed through environment variables, which the new
process will check for and then remove the variable from the
environment.
Lots of prickly edge cases to support here.
Without binfmt_misc:
- Passes the FD to FEXLoader directly.
- Requires duplicating the FD if it has O_CLOEXEC on the FD.
With binfmt_misc:
- Shebang file, pass directly to FEXLoader, just like without binfmt.
- x86 ELF Files, rely on the kernel's binfmt_misc support here.
- Unsupported ELF files, let kernel handle it through binfmt_misc
Argument handling:
- The application can pass in no arguments.
- Means our application configurations were failing to find a config
- Also various checks in the frontend were failing.
- If opened through an FD, find the symlink for that FD for the
application configuration instead.
Side note:
Fixed a performance issue in execve where when we were checking for file
format support. Either ELF or Shebang files, we were reading the /whole/
file upfront. We only need to read a header worth of ELF files, and only
257 bytes if it is potentially a shebang file. Should dramatically
reduce some application's execve times.
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