From a84b540b65f7a68948e6e804c09c21f1ff36e795 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 99ec060a2..1c2eb7d86 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 90a574339..7cd434f3a 100644
--- a/vmm/src/lib.rs
+++ b/vmm/src/lib.rs
@@ -2158,6 +2158,7 @@ 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>>,
 }