From ed27e93b8103fb51cc8ddf03f7ec3b1b14781c20 Mon Sep 17 00:00:00 2001
From: Philipp Schuster <philipp.schuster@cyberus-technology.de>
Date: Thu, 19 Jun 2025 18:26:04 +0200
Subject: [PATCH] vmm: remove special serialization of network FDs

Deserializing values as `-1` makes sense to prevent errors, so let's
keep it. However, serializing them differently adds confusion. For
example, a `ch-remote info` call should not report `-1` but the actual
FDs.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
---
 vmm/src/config.rs    | 27 ++-------------------------
 vmm/src/vm_config.rs | 21 ++-------------------
 2 files changed, 4 insertions(+), 44 deletions(-)

diff --git a/vmm/src/config.rs b/vmm/src/config.rs
index 1d8979210..af89539f0 100644
--- a/vmm/src/config.rs
+++ b/vmm/src/config.rs
@@ -2205,40 +2205,17 @@ pub struct RestoredNetConfig {
     pub id: String,
     #[serde(default)]
     pub num_fds: usize,
-    // Special (de)serialize handling:
+    // Special deserialize handling:
     // A serialize-deserialize cycle typically happens across processes.
     // Therefore, we don't serialize FDs, and whatever value is here after
     // deserialization is invalid.
     //
     // Valid FDs are transmitted via a different channel (SCM_RIGHTS message)
     // and will be populated into this struct on the destination VMM eventually.
-    #[serde(
-        default,
-        serialize_with = "serialize_restorednetconfig_fds",
-        deserialize_with = "deserialize_restorednetconfig_fds"
-    )]
+    #[serde(default, deserialize_with = "deserialize_restorednetconfig_fds")]
     pub fds: Option<Vec<i32>>,
 }
 
-fn serialize_restorednetconfig_fds<S>(
-    x: &Option<Vec<i32>>,
-    s: S,
-) -> std::result::Result<S::Ok, S::Error>
-where
-    S: serde::Serializer,
-{
-    if let Some(x) = x {
-        // If the live-migration path is used properly, new FDs are passed as
-        // SCM_RIGHTS message. So, we don't get them from the serialized JSON
-        // anyway.
-        debug!("FDs in 'RestoredNetConfig' won't be serialized as they are most likely invalid after deserialization. Serializing them as -1.");
-        let invalid_fds = vec![-1; x.len()];
-        s.serialize_some(&invalid_fds)
-    } else {
-        s.serialize_none()
-    }
-}
-
 fn deserialize_restorednetconfig_fds<'de, D>(
     d: D,
 ) -> std::result::Result<Option<Vec<i32>>, D::Error>
diff --git a/vmm/src/vm_config.rs b/vmm/src/vm_config.rs
index 49e3e9596..7021f9e9c 100644
--- a/vmm/src/vm_config.rs
+++ b/vmm/src/vm_config.rs
@@ -324,17 +324,13 @@ pub struct NetConfig {
     pub vhost_mode: VhostMode,
     #[serde(default)]
     pub id: Option<String>,
-    // Special (de)serialize handling:
+    // Special deserialize handling:
     // Therefore, we don't serialize FDs, and whatever value is here after
     // deserialization is invalid.
     //
     // Valid FDs are transmitted via a different channel (SCM_RIGHTS message)
     // and will be populated into this struct on the destination VMM eventually.
-    #[serde(
-        default,
-        serialize_with = "serialize_netconfig_fds",
-        deserialize_with = "deserialize_netconfig_fds"
-    )]
+    #[serde(default, deserialize_with = "deserialize_netconfig_fds")]
     pub fds: Option<Vec<i32>>,
     #[serde(default)]
     pub rate_limiter_config: Option<RateLimiterConfig>,
@@ -372,19 +368,6 @@ pub fn default_netconfig_queue_size() -> u16 {
     DEFAULT_NET_QUEUE_SIZE
 }
 
-fn serialize_netconfig_fds<S>(x: &Option<Vec<i32>>, s: S) -> Result<S::Ok, S::Error>
-where
-    S: serde::Serializer,
-{
-    if let Some(x) = x {
-        debug!("FDs in 'NetConfig' won't be serialized as they are most likely invalid after deserialization; using -1.");
-        let invalid_fds = vec![-1; x.len()];
-        s.serialize_some(&invalid_fds)
-    } else {
-        s.serialize_none()
-    }
-}
-
 fn deserialize_netconfig_fds<'de, D>(d: D) -> Result<Option<Vec<i32>>, D::Error>
 where
     D: serde::Deserializer<'de>,