Get default cache dir from FIL_PROOFS_CACHE_DIR.

storage-proofs/core/src/settings.rs

@@ -1,3 +1,4 @@
+use std::env;
 use std::sync::Mutex;
 
 use config::{Config, ConfigError, Environment, File};
@@ -10,6 +11,7 @@ lazy_static! {
 }
 
 const SETTINGS_PATH: &str = "./rust-fil-proofs.config.toml";
+const PREFIX: &str = "FIL_PROOFS";
 
 #[derive(Debug, Serialize, Deserialize)]
 #[serde(default)]
@@ -41,18 +43,31 @@ impl Default for Settings {
             rows_to_discard: 2,
             sdr_parents_cache_size: 2_048,
             window_post_synthesis_num_cpus: num_cpus::get() as u32,
+            // `parameter_cache` does not use the cache() mechanism because it is now used
+            // for durable, canonical Groth parameters and verifying keys.
+            // The name is retained for backwards compatibility.
             parameter_cache: "/var/tmp/filecoin-proof-parameters/".to_string(),
-            parent_cache: "/var/tmp/filecoin-parents".to_string(),
+            parent_cache: cache("filecoin-parents"),
         }
     }
 }
 
+/// All cache files and directories paths should be constructed using this function,
+/// which its base directory from the FIL_PROOFS_CACHE_DIR env var, and defaults to /var/tmp.
+/// Note that FIL_PROOFS_CACHE_DIR is not a first class setting and can only be set by env var.
+fn cache(s: &str) -> String {
+    let cache_var = format!("{}_CACHE_DIR", PREFIX);
+    let mut cache_name = env::var(cache_var).unwrap_or_else(|_| "/var/tmp/".to_string());
+    cache_name.push_str(s);
+    cache_name
+}
+
 impl Settings {
     fn new() -> Result<Settings, ConfigError> {
         let mut s = Config::new();
 
         s.merge(File::with_name(SETTINGS_PATH).required(false))?;
-        s.merge(Environment::with_prefix("FIL_PROOFS"))?;
+        s.merge(Environment::with_prefix(PREFIX))?;
 
         s.try_into()
     }