vmm, main: Add optional "hotplug_size" to --mem

This specifies how much address space should be reserved for hotplugging
of RAM. This space is reserved by adding move the start of the device
area by the desired amount.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/config.rs

@@ -248,6 +248,8 @@ pub struct MemoryConfig {
     pub file: Option<PathBuf>,
     #[serde(default)]
     pub mergeable: bool,
+    #[serde(default)]
+    pub hotplug_size: Option<u64>,
 }
 
 impl MemoryConfig {
@@ -259,6 +261,7 @@ impl MemoryConfig {
         let mut file_str: &str = "";
         let mut mergeable_str: &str = "";
         let mut backed = false;
+        let mut hotplug_str: &str = "";
 
         for param in params_list.iter() {
             if param.starts_with("size=") {
@@ -268,6 +271,8 @@ impl MemoryConfig {
                 file_str = &param[5..];
             } else if param.starts_with("mergeable=") {
                 mergeable_str = &param[10..];
+            } else if param.starts_with("hotplug_size=") {
+                hotplug_str = &param[13..]
             }
         }
 
@@ -285,6 +290,11 @@ impl MemoryConfig {
             size: parse_size(size_str)?,
             file,
             mergeable: parse_on_off(mergeable_str)?,
+            hotplug_size: if hotplug_str == "" {
+                None
+            } else {
+                Some(parse_size(hotplug_str)?)
+            },
         })
     }
 }
@@ -295,6 +305,7 @@ impl Default for MemoryConfig {
             size: DEFAULT_MEMORY_MB << 20,
             file: None,
             mergeable: false,
+            hotplug_size: None,
         }
     }
 }