From 0d5bde2181d65a684ddd08e4085339cc29882a7e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aur=C3=A9lien=20Bombo?= <abombo@microsoft.com>
Date: Fri, 1 May 2026 15:10:04 -0500
Subject: [PATCH] runtime-rs: virtio-fs: plumb virtio_fs_queue_size to qemu/CH
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The shared filesystem device builder in `prepare_virtiofs` was
hardcoding `queue_size = 0` and `queue_num = 0` on the `ShareFsConfig`
it hands to the hypervisor, ignoring `SharedFsInfo.virtio_fs_queue_size`
parsed from `configuration.toml` entirely.

For qemu, this is silently broken: the cmdline generator's
`DeviceVhostUserFs::set_queue_size` treats 0 as "not set" and skips the
`queue-size=` argument when emitting the `vhost-user-fs-pci` device, so
QEMU falls back to its built-in default of 128, regardless of what the
user configured.

For Cloud Hypervisor it happens to work in practice today, but only
because `ch::handle_share_fs_device` and `TryFrom<ShareFsSettings> for
FsConfig` substitute a hardcoded 1024 when the incoming
`queue_num`/`queue_size` are zero. That fallback masks the real bug; the
toml value still never reaches the VMM.

Add a `get_shared_fs_info` accessor on `DeviceManager` mirroring the
existing `get_block_device_info` helper, and use it in
`prepare_virtiofs` to populate `ShareFsConfig.queue_size` from
`SharedFsInfo.virtio_fs_queue_size`. Use a single virtqueue
(`queue_num = 1`), matching what runtime-go hardcodes for both qemu
(govmm `QemuFSParams` does not emit `num-queues=`) and CH
(`numQueues := int32(1)` in `clh.go`).

The CH-side fallback and the CH config template are addressed in a
follow-up commit.

Signed-off-by: Aurélien Bombo <abombo@microsoft.com>
---
 .../crates/hypervisor/src/device/device_manager.rs     | 10 +++++++++-
 .../crates/resource/src/share_fs/share_virtio_fs.rs    | 10 +++++++---
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/runtime-rs/crates/hypervisor/src/device/device_manager.rs b/src/runtime-rs/crates/hypervisor/src/device/device_manager.rs
index 864494f2e4..78c5a02166 100644
--- a/src/runtime-rs/crates/hypervisor/src/device/device_manager.rs
+++ b/src/runtime-rs/crates/hypervisor/src/device/device_manager.rs
@@ -12,7 +12,7 @@ use std::{
 
 use anyhow::{anyhow, Context, Result};
 use kata_sys_util::rand::RandomBytes;
-use kata_types::config::hypervisor::{BlockDeviceInfo, TopologyConfigInfo, VIRTIO_SCSI};
+use kata_types::config::hypervisor::{BlockDeviceInfo, SharedFsInfo, TopologyConfigInfo, VIRTIO_SCSI};
 use tokio::sync::{Mutex, RwLock};
 
 use crate::{
@@ -126,6 +126,10 @@ impl DeviceManager {
         self.hypervisor.hypervisor_config().await.blockdev_info
     }
 
+    async fn get_shared_fs_info(&self) -> SharedFsInfo {
+        self.hypervisor.hypervisor_config().await.shared_fs
+    }
+
     async fn try_add_device(&mut self, device_id: &str) -> Result<()> {
         // find the device
         let device = self
@@ -714,6 +718,10 @@ pub async fn get_block_device_info(d: &RwLock<DeviceManager>) -> BlockDeviceInfo
     d.read().await.get_block_device_info().await
 }
 
+pub async fn get_shared_fs_info(d: &RwLock<DeviceManager>) -> SharedFsInfo {
+    d.read().await.get_shared_fs_info().await
+}
+
 #[cfg(test)]
 mod tests {
     use super::DeviceManager;
diff --git a/src/runtime-rs/crates/resource/src/share_fs/share_virtio_fs.rs b/src/runtime-rs/crates/resource/src/share_fs/share_virtio_fs.rs
index 8328355ed5..b665846028 100644
--- a/src/runtime-rs/crates/resource/src/share_fs/share_virtio_fs.rs
+++ b/src/runtime-rs/crates/resource/src/share_fs/share_virtio_fs.rs
@@ -12,7 +12,7 @@ use tokio::sync::RwLock;
 
 use hypervisor::{
     device::{
-        device_manager::{do_handle_device, do_update_device, DeviceManager},
+        device_manager::{do_handle_device, do_update_device, get_shared_fs_info, DeviceManager},
         driver::{ShareFsMountConfig, ShareFsMountOperation, ShareFsMountType},
         DeviceConfig,
     },
@@ -54,8 +54,12 @@ pub(crate) async fn prepare_virtiofs(
         sock_path: generate_sock_path(root),
         mount_tag: String::from(MOUNT_GUEST_TAG),
         fs_type: fs_type.to_string(),
-        queue_size: 0,
-        queue_num: 0,
+        // Pull virtio-fs queue size from the hypervisor config so the value
+        // configured via `virtio_fs_queue_size` in the toml actually reaches
+        // the VMM device line. There is currently no toml knob for the number
+        // of virtqueues, so we use a single queue (matching the prior default).
+        queue_size: get_shared_fs_info(d).await.virtio_fs_queue_size as u64,
+        queue_num: 1,
         options: vec![],
         mount_config: None,
     };