[pve-devel] [PATCH docs 3/3] qm: virtiofs: drop writeback cache

[Fiona Ebner <f.ebner@proxmox.com>]

VirtIO-fs using writeback cache seems very broken at the moment. If a
guest accesses a file (even just using 'touch'), that the host is
currently writing, the guest can permanently end up with a truncated
version of that file. Even subsequent operations like moving the file,
will not result in the correct file being visible, but just rename the
truncated one.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 qm.adoc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/qm.adoc b/qm.adoc
index 539912a..1babb82 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -1309,7 +1309,7 @@ has been configured in the resource mapping. Additionally, you can set the
 `cache` option to either `always`, `never`, `metadata`, or `auto` (default:
 `auto`), depending on your requirements. How the different caching modes behave
 can be read https://lwn.net/Articles/774495/[here under the "Caching Modes"
-section]. To enable writeback cache set `writeback` to `1`.
+section].
 
 Virtiofsd supports ACL and xattr passthrough (can be enabled with the
 `expose-acl` and `expose-xattr` options), allowing the guest to access ACLs and
@@ -1327,7 +1327,7 @@ applications do their own caching.
 ----
 qm set <vmid> -virtiofs0 dirid=<dirid>,cache=always,direct-io=1
 qm set <vmid> -virtiofs1 <dirid>,cache=never,expose-xattr=1
-qm set <vmid> -virtiofs2 <dirid>,expose-acl=1,writeback=1
+qm set <vmid> -virtiofs2 <dirid>,expose-acl=1
 ----
 
 To temporarily mount virtio-fs in a guest VM with the Linux kernel virtio-fs
-- 
2.39.5



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