From 0d2e2cd4c3fe8fa53f2d4a8a3de2e637a405aeb1 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 ded127202..5acab28c3 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 7af624fc3..4091763cb 100644
--- a/vmm/src/config.rs
+++ b/vmm/src/config.rs
@@ -2191,11 +2191,27 @@ 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)
@@ -2812,6 +2828,7 @@ 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 112be7e25..ec12c9002 100644
--- a/vmm/src/lib.rs
+++ b/vmm/src/lib.rs
@@ -2100,6 +2100,7 @@ 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 376f2057d..f83d14db6 100644
--- a/vmm/src/vm_config.rs
+++ b/vmm/src/vm_config.rs
@@ -593,4 +593,10 @@ 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>>,
 }