From db7938992d554ce633cd15cfd8144b232430f657 Mon Sep 17 00:00:00 2001
From: deeplow <47065258+deeplow@users.noreply.github.com>
Date: Mon, 27 Jan 2025 13:49:56 +0000
Subject: [PATCH] qrexec: add info about QREXEC_REMOTE_DOMAIN

Add information about `QREXEC_REMOTE_DOMAIN` which is still on the qrexec2.md file but not on the V3. However, this still applies, so it should be documented.
---
 developer/services/qrexec.md | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/developer/services/qrexec.md b/developer/services/qrexec.md
index edee53b1..ded9fa97 100644
--- a/developer/services/qrexec.md
+++ b/developer/services/qrexec.md
@@ -109,10 +109,6 @@ whether to allow the request, what VM to redirect the execution to, and what use
 Note that if the request is redirected (`target=` parameter), policy action remains the same -- even if there is another rule which would otherwise deny such request.
 If no policy rule is matched, the action is denied.
 
-In the target VM, a file in either of the following locations must exist, containing the file name of the program that will be invoked, or being that program itself -- in which case it must have executable permission set (`chmod +x`):
-  - `/etc/qubes-rpc/RPC_ACTION_NAME` when you make it in the template qube;
-  - `/usr/local/etc/qubes-rpc/RPC_ACTION_NAME` for making it only in an app qube.
-
 Files in `/run/qubes/policy.d/` are deleted when the system is rebooted.
 This is useful for temporary policy that contains the name or UUID of a disposable VM, which will not be meaningful after the system has rebooted.
 Such policy files can be created manually, but they are usually created automatically by a Qrexec call to dom0.
@@ -140,6 +136,17 @@ It is also possible to call service without specific client program -- in which
 $ qrexec-client-vm target_vm_name RPC_ACTION_NAME
 ```
 
+### Answering an RPC call
+
+In other for a RPC call to be answered in the target VM, a file in either of the following locations must exist, containing the file name of the program that will be invoked, or being that program itself -- in which case it must have executable permission set (`chmod +x`):
+  - `/etc/qubes-rpc/RPC_ACTION_NAME` when you make it in the template qube;
+  - `/usr/local/etc/qubes-rpc/RPC_ACTION_NAME` for making it only in an app qube.
+
+The source VM name can then be accessed in the server process via
+`QREXEC_REMOTE_DOMAIN` environment variable. (Note the source VM has *no*
+control over the name provided in this variable--the name of the VM is
+provided by dom0, and so is trusted.)
+
 ### Specifying VMs: tags, types, targets, etc.
 
 There are severals methods for specifying source/target VMs in RPC policies.