From: Daan De Meyer <daan.j.demeyer@gmail.com>
Date: Fri, 3 May 2024 14:24:50 +0000 (+0200)
Subject: qemu: Configure caching properly
X-Git-Tag: v23.1~76^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d31639b2e6d6fc83f8a411e5f07a975c84e0f3d6;p=thirdparty%2Fmkosi.git

qemu: Configure caching properly

For the scratch device, we can use unsafe caching as it's thrown
away immediately after the machine shuts down. For the root disk,
we can use unsafe caching only if --ephemeral is enabled.
---

diff --git a/mkosi/qemu.py b/mkosi/qemu.py
index 86b673f5d..670283539 100644
--- a/mkosi/qemu.py
+++ b/mkosi/qemu.py
@@ -36,6 +36,7 @@ from mkosi.config import (
     format_bytes,
     systemd_tool_version,
     want_selinux_relabel,
+    yes_no,
 )
 from mkosi.log import ARG_DEBUG, die
 from mkosi.mounts import finalize_source_mounts
@@ -1035,8 +1036,9 @@ def run_qemu(args: Args, config: Config) -> None:
 
         if want_scratch(config):
             scratch = stack.enter_context(generate_scratch_fs(config))
+            cache = "cache.writeback=on,cache.direct=on,cache.no-flush=yes"
             cmdline += [
-                "-drive", f"if=none,id=scratch,file={scratch},format=raw,discard=on",
+                "-drive", f"if=none,id=scratch,file={scratch},format=raw,discard=on,{cache}",
                 "-device", "scsi-hd,drive=scratch",
             ]
             kcl += [f"systemd.mount-extra=LABEL=scratch:/var/tmp:{config.distribution.filesystem()}"]
@@ -1051,7 +1053,8 @@ def run_qemu(args: Args, config: Config) -> None:
             cmdline += ["-initrd", config.output_dir_or_cwd() / config.output_split_initrd]
 
         if config.output_format in (OutputFormat.disk, OutputFormat.esp):
-            cmdline += ["-drive", f"if=none,id=mkosi,file={fname},format=raw,discard=on",
+            cache = f"cache.writeback=on,cache.direct=on,cache.no-flush={yes_no(config.ephemeral)}"
+            cmdline += ["-drive", f"if=none,id=mkosi,file={fname},format=raw,discard=on,{cache}",
                         "-device", f"scsi-{'cd' if config.qemu_cdrom else 'hd'},drive=mkosi,bootindex=1"]
 
         if (