fish: Support converting systemd-nspawn paths to and from host paths

Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

fish/functions/cbl_bld_llvm_korg.fish

@@ -59,7 +59,7 @@ function cbl_bld_llvm_korg -d "Build (and optionally test) LLVM for kernel.org"
         for tc in (fd -a -d 1 -t d . $tmp_llvm_install)
             for src in $CBL_SRC_C/linux $CBL_SRC_C/linux-stable-$CBL_STABLE_VERSIONS
                 if using_nspawn
-                    sd_nspawn -r 'cbl_lkt --linux-folder '(nspawn_adjust_path $src)' --llvm-prefix '(nspawn_adjust_path $tc)
+                    sd_nspawn -r 'cbl_lkt --linux-folder '(nspawn_path -c $src)' --llvm-prefix '(nspawn_path -c $tc)
                 else if dbx_has_82a69f0
                     dbxe -- fish -c "cbl_lkt --linux-folder $src --llvm-prefix $tc"
                 else

fish/functions/cbl_test_kvm.fish

@@ -56,7 +56,7 @@ function cbl_test_kvm -d "Test KVM against a Clang built kernel with QEMU"
                     mkdir -p $TMP_FOLDER
                     cp -v /boot/vmlinuz-linux $TMP_FOLDER/bzImage
                     if using_nspawn
-                        sd_nspawn -r 'kboot -a x86_64 -k '(nspawn_adjust_path $TMP_FOLDER)'/bzImage -t 30s'
+                        sd_nspawn -r 'kboot -a x86_64 -k '(nspawn_path -c $TMP_FOLDER)'/bzImage -t 30s'
                     else if dbx_has_82a69f0
                         dbxe -- fish -c "kboot -a x86_64 -k $TMP_FOLDER/bzImage -t 30s"
                     else

fish/functions/mchsh.fish

@@ -25,5 +25,5 @@ function mchsh -d "Wrapper around 'machinectl shell'"
     # Use fish's --init-commands to drop into the current working directory,
     # instead of $HOME, which is not really useful if working on the host and
     # wanting to drop into the guest to work.
-    machinectl shell -q $user_host $SHELL -C 'cd '(nspawn_adjust_path $PWD) $mchsh_args
+    machinectl shell -q $user_host $SHELL -C 'cd '(nspawn_path -c $PWD) $mchsh_args
 end

fish/functions/nspawn_adjust_path.fish

@@ -0,0 +1,33 @@
+#!/usr/bin/env fish
+# SPDX-License-Identifier: MIT
+# Copyright (C) 2024 Nathan Chancellor
+
+function nspawn_path -d "Translate /home paths into systemd-nspawn or host"
+    set mode $argv[1]
+    set path $argv[2]
+    set run_host /run/host
+
+    # The path only needs to be adjusted when it actually starts with whatever
+    # the current $HOME value is, otherwise we assume that it is either already
+    # in the appropriate format or it does not need to be converted.
+    if string match -qr ^$HOME $path
+        switch $mode
+            # In container mode, the /home path should be prefixed with /run/host
+            case -c --container
+                if not string match -qr ^$run_host $path
+                    set prefix $run_host
+                end
+                printf '%s%s\n' $prefix $path
+
+            # In host mode, /run/host should be stripped from /home
+            case -H --host
+                if string match -qr ^/home $path
+                    echo $path
+                else
+                    string replace -m1 $run_host '' $path
+                end
+        end
+    else
+        echo $path
+    end
+end