From 1e4e03d110b74a3977a820c80bebe2fa33df3990 Mon Sep 17 00:00:00 2001
From: Bo Chen <chen.bo@intel.com>
Date: Fri, 14 Apr 2023 16:44:41 -0700
Subject: [PATCH] vmm: config: Extend 'VmConfig' with 'preserved_fds'

Preserved FDs are the ones that share the same life-time as its holding
VmConfig instance, such as FDs for creating TAP devices.

Preserved FDs will stay open as long as the holding VmConfig instance is
valid, and will be closed when the holding VmConfig instance is destroyed.

Signed-off-by: Bo Chen <chen.bo@intel.com>
---
 src/main.rs          |  1 +
 vmm/src/config.rs    | 17 +++++++++++++++++
 vmm/src/lib.rs       |  1 +
 vmm/src/vm_config.rs |  6 ++++++
 4 files changed, 25 insertions(+)

diff --git a/src/main.rs b/src/main.rs
index 2e70913f8..27e67d772 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -722,6 +722,7 @@ mod unit_tests {
             gdb: false,
             platform: None,
             tpm: None,
+            preserved_fds: None,
         };
 
         assert_eq!(expected_vm_config, result_vm_config);
diff --git a/vmm/src/config.rs b/vmm/src/config.rs
index 687175f6e..1f95c82e8 100644
--- a/vmm/src/config.rs
+++ b/vmm/src/config.rs
@@ -2093,11 +2093,27 @@ impl VmConfig {
             gdb,
             platform,
             tpm,
+            preserved_fds: None,
         };
         config.validate().map_err(Error::Validation)?;
         Ok(config)
     }
 
+    /// # Safety
+    /// To use this safely, the caller must guarantee that the input
+    /// fds are all valid.
+    pub unsafe fn add_preserved_fds(&mut self, mut fds: Vec<i32>) {
+        if fds.is_empty() {
+            return;
+        }
+
+        if let Some(preserved_fds) = &self.preserved_fds {
+            fds.append(&mut preserved_fds.clone());
+        }
+
+        self.preserved_fds = Some(fds);
+    }
+
     #[cfg(feature = "tdx")]
     pub fn is_tdx_enabled(&self) -> bool {
         self.platform.as_ref().map(|p| p.tdx).unwrap_or(false)
@@ -2714,6 +2730,7 @@ mod tests {
             gdb: false,
             platform: None,
             tpm: None,
+            preserved_fds: None,
         };
 
         assert!(valid_config.validate().is_ok());
diff --git a/vmm/src/lib.rs b/vmm/src/lib.rs
index 146f4e56c..723cd4e79 100644
--- a/vmm/src/lib.rs
+++ b/vmm/src/lib.rs
@@ -2136,6 +2136,7 @@ mod unit_tests {
             gdb: false,
             platform: None,
             tpm: None,
+            preserved_fds: None,
         }))
     }
 
diff --git a/vmm/src/vm_config.rs b/vmm/src/vm_config.rs
index f9740e57d..d26a85c06 100644
--- a/vmm/src/vm_config.rs
+++ b/vmm/src/vm_config.rs
@@ -596,4 +596,10 @@ pub struct VmConfig {
     pub gdb: bool,
     pub platform: Option<PlatformConfig>,
     pub tpm: Option<TpmConfig>,
+    // Preseved FDs are the ones that share the same life-time as its holding
+    // VmConfig instance, such as FDs for creating TAP devices.
+    // Perserved FDs will stay open as long as the holding VmConfig instance is
+    // valid, and will be closed when the holding VmConfig instance is destroyed.
+    #[serde(skip)]
+    pub preserved_fds: Option<Vec<i32>>,
 }