Added '--use-extended-yaml' option

Author: stevenengler

docs/shadow_config_overview.md

@@ -77,7 +77,10 @@ Acceptable unit *prefixes* are:
 
 Examples: `20 B`, `100 MB`, `100 megabyte`, `10 kibibytes`, `30 MiB`, `1024 Mbytes`
 
-## YAML Extensions
+## YAML Extensions (Experimental)
+
+Shadow has experimental support for extended YAML conventions. These can be
+enabled using the `--use-extended-yaml true` command line option.
 
 ### Merge/Override Mappings
 

docs/shadow_config_spec.md

@@ -84,6 +84,7 @@ hosts:
 - [`experimental.use_cpu_pinning`](#experimentaluse_cpu_pinning)
 - [`experimental.use_dynamic_runahead`](#experimentaluse_dynamic_runahead)
 - [`experimental.use_explicit_block_message`](#experimentaluse_explicit_block_message)
+- [`experimental.use_extended_yaml`](#experimentaluse_extended_yaml)
 - [`experimental.use_legacy_working_dir`](#experimentaluse_legacy_working_dir)
 - [`experimental.use_libc_preload`](#experimentaluse_libc_preload)
 - [`experimental.use_memory_manager`](#experimentaluse_memory_manager)
@@ -480,6 +481,14 @@ Type: Bool
 Send message to managed process telling it to stop spinning when a syscall
 blocks.
 
+#### `experimental.use_extended_yaml`
+
+Default: false  
+Type: Bool
+
+Enable extended YAML conventions (merge keys and extension fields). Can only be
+enabled on the command line (enabling in the configuration file is a no-op).
+
 #### `experimental.use_legacy_working_dir`
 
 Default: false  

src/main/core/main.rs

@@ -61,8 +61,12 @@ pub fn run_shadow<'a>(args: Vec<&'a OsStr>) -> anyhow::Result<()> {
     }
     .into();
 
+    // this option is weird since it's a configuration option but we need to read it before merging
+    // with the configuration file
+    let use_extended_yaml = options.experimental.use_extended_yaml.unwrap_or_default();
+
     // load the configuration yaml
-    let config_file = load_config_file(&config_filename)
+    let config_file = load_config_file(&config_filename, use_extended_yaml)
         .with_context(|| format!("Failed to load configuration file {}", config_filename))?;
 
     // generate the final shadow configuration from the config file and cli options
@@ -179,7 +183,10 @@ pub fn run_shadow<'a>(args: Vec<&'a OsStr>) -> anyhow::Result<()> {
     Ok(())
 }
 
-fn load_config_file(filename: impl AsRef<std::path::Path>) -> anyhow::Result<ConfigFileOptions> {
+fn load_config_file(
+    filename: impl AsRef<std::path::Path>,
+    extended_yaml: bool,
+) -> anyhow::Result<ConfigFileOptions> {
     let file = std::fs::File::open(filename).context("Could not open config file")?;
 
     // serde's default behaviour is to silently ignore duplicate keys during deserialization so we
@@ -191,23 +198,25 @@ fn load_config_file(filename: impl AsRef<std::path::Path>) -> anyhow::Result<Con
     let mut config_file: serde_yaml::Value =
         serde_yaml::from_reader(file).context("Could not parse configuration file as yaml")?;
 
-    // apply the merge before removing extension fields
-    config_file
-        .apply_merge()
-        .context("Could not merge '<<' keys")?;
-
-    // remove top-level extension fields
-    if let serde_yaml::Value::Mapping(ref mut mapping) = &mut config_file {
-        // remove entries having a key beginning with "x-" (follows docker's convention:
-        // https://docs.docker.com/compose/compose-file/#extension)
-        mapping.retain(|key, _value| {
-            if let serde_yaml::Value::String(key) = key {
-                if key.starts_with("x-") {
-                    return false;
+    if extended_yaml {
+        // apply the merge before removing extension fields
+        config_file
+            .apply_merge()
+            .context("Could not merge '<<' keys")?;
+
+        // remove top-level extension fields
+        if let serde_yaml::Value::Mapping(ref mut mapping) = &mut config_file {
+            // remove entries having a key beginning with "x-" (follows docker's convention:
+            // https://docs.docker.com/compose/compose-file/#extension)
+            mapping.retain(|key, _value| {
+                if let serde_yaml::Value::String(key) = key {
+                    if key.starts_with("x-") {
+                        return false;
+                    }
                 }
-            }
-            true
-        });
+                true
+            });
+        }
     }
 
     Ok(serde_yaml::from_value(config_file).context("Could not parse configuration file")?)

src/main/core/support/configuration.rs

@@ -449,6 +449,13 @@ pub struct ExperimentalOptions {
     #[clap(long, value_name = "seconds")]
     #[clap(help = EXP_HELP.get("unblocked_vdso_latency").unwrap().as_str())]
     pub unblocked_vdso_latency: Option<units::Time<units::TimePrefix>>,
+
+    /// Enable extended YAML conventions (merge keys and extension fields). Can only be enabled on
+    /// the command line (enabling in the configuration file is a no-op).
+    #[clap(hide_short_help = true)]
+    #[clap(long, value_name = "bool")]
+    #[clap(help = EXP_HELP.get("use_extended_yaml").unwrap().as_str())]
+    pub use_extended_yaml: Option<bool>,
 }
 
 impl ExperimentalOptions {
@@ -500,6 +507,7 @@ impl Default for ExperimentalOptions {
             host_heartbeat_log_info: Some(IntoIterator::into_iter([LogInfoFlag::Node]).collect()),
             host_heartbeat_interval: None,
             strace_logging_mode: Some(StraceLoggingMode::Off),
+            use_extended_yaml: Some(false),
         }
     }
 }