Refactor and add documentation

Signed-off-by: James Sturtevant <[email protected]>

crates/containerd-shim-wasm/src/sandbox/containerd.rs

@@ -454,76 +454,67 @@ impl Client {
         };
 
         log::info!("found manifest with WASM OCI image format.");
-        // This label is unique across runtimes and versions
+        // This label is unique across runtimes and version of the shim running
         // a precompiled component/module will not work across different runtimes or versions
         let label = precompile_label(T::info());
         match image.labels.get(&label) {
             Some(precompile_digest) if T::can_precompile() => {
-                log::info!("found precompiled image");
+                log::info!("found precompiled module in cache");
                 let precompiled = self.read_content(precompile_digest)?;
-                Ok((
+                return Ok((
                     vec![WasmLayer {
                         config: image_config_descriptor.clone(),
                         layer: precompiled,
                     }],
                     platform,
                 ))
             }
-            None if T::can_precompile() => {
-                log::info!("precompiling module");
-                let layers = manifest
-                    .layers()
-                    .iter()
-                    .filter(|x| is_wasm_layer(x.media_type(), T::supported_layers_types()))
-                    .map(|config| self.read_content(config.digest()))
-                    .collect::<Result<Vec<_>>>()?;
-
-                log::debug!("precompile complete and saving content");
-                let precompiled = engine.precompile(layers.as_slice())?;
-                let precompiled_content =
-                    self.save_content(precompiled.clone(), image_digest.clone(), T::info())?;
-
-                log::debug!("updating image with compiled content digest");
-                image
-                    .labels
-                    .insert(label, precompiled_content.digest.clone());
-                self.update_image(image)?;
-
-                // The original image is considered a root object, by adding a ref to the new compiled content
-                // We tell to containerd to not garbage collect the new content until this image is removed from the system
-                // this ensures that we keep the content around after the lease is dropped
-                log::debug!("updating content with precompile digest to avoid garbage collection");
-                let mut image_content = self.get_info(image_digest.clone())?;
-                image_content.labels.insert(
-                    "containerd.io/gc.ref.content.precompile".to_string(),
-                    precompiled_content.digest.clone(),
-                );
-                self.update_info(image_content)?;
-
-                Ok((
-                    vec![WasmLayer {
-                        config: image_config_descriptor.clone(),
-                        layer: precompiled,
-                    }],
-                    platform,
-                ))
-            }
-            _ => {
-                log::info!("using module from OCI layers");
-                let layers = manifest
+            _ => {}
+        }
+
+        let layers = manifest
                     .layers()
                     .iter()
                     .filter(|x| is_wasm_layer(x.media_type(), T::supported_layers_types()))
-                    .map(|config| {
-                        self.read_content(config.digest()).map(|module| WasmLayer {
-                            config: config.clone(),
-                            layer: module,
-                        })
-                    })
-                    .collect::<Result<Vec<_>>>()?;
-                Ok((layers, platform))
-            }
+                    .map(|config| self.read_content(config.digest())).collect::<Result<Vec<_>>>()?;
+
+        if T::can_precompile()  {
+            log::info!("precompiling module");
+            let precompiled = engine.precompile(layers.as_slice())?;
+            let precompiled_content =
+                self.save_content(precompiled.clone(), image_digest.clone(), T::info())?;
+
+            log::debug!("updating image with compiled content digest");
+            image.labels.insert(label, precompiled_content.digest.clone());
+            self.update_image(image)?;
+
+            // The original image is considered a root object, by adding a ref to the new compiled content
+            // We tell to containerd to not garbage collect the new content until this image is removed from the system
+            // this ensures that we keep the content around after the lease is dropped
+            log::debug!("updating content with precompile digest to avoid garbage collection");
+            let mut image_content = self.get_info(image_digest.clone())?;
+            image_content.labels.insert(
+                "containerd.io/gc.ref.content.precompile".to_string(),
+                precompiled_content.digest.clone(),
+            );
+            self.update_info(image_content)?;
+
+            return Ok((
+                vec![WasmLayer {
+                    config: image_config_descriptor.clone(),
+                    layer: precompiled,
+                }],
+                platform,
+            ))
         }
+
+        log::info!("using module from OCI layers");
+        let layers = layers.into_iter().map(|module| WasmLayer {
+            config: image_config_descriptor.clone(),
+            layer: module,
+        }).collect::<Vec<_>>();
+        Ok((layers, platform))
+
     }
 }
 

docs/oci-descision-flow.md

@@ -0,0 +1,48 @@
+# OCI pre-compilation
+
+The OCI images layers are loaded from containerd.  If the runtime supports pre-compilation the images will be precompiled and cached using the containerd content store.  
+
+```mermaid
+graph TD
+    start[Task new]
+    imgconfig[Load image config from containerd]
+    iswasm{Arch==wasm?}
+    alreadycompiled{Does image label for shim runtime version exist? runwasi.io/precompiled/runtime/version
+    }
+    startcontainer[Create Container]
+    precompiledenabled{Is precompiling enabled in shim?}
+    precompiledenabled2{Is precompiling enabled in shim?}
+    fetchcache[Fetch cached precompiled layer from containerd content store]
+    precompile[Precompile using wasm runtime]
+    loadoci[Load OCI layers from containerd]
+    storecache[Store precompiled layer in containerd content store]
+
+    start --> imgconfig --> iswasm
+    iswasm -- yes --> precompiledenabled 
+    iswasm -- no wasm will be loaded from file inside image --> startcontainer
+
+    precompiledenabled -- yes --> alreadycompiled
+    precompiledenabled -- no --> loadoci --> precompiledenabled2 
+
+    alreadycompiled -- yes --> fetchcache --> startcontainer
+    alreadycompiled -- no --> loadoci 
+
+    precompiledenabled2 -- yes --> precompile --> storecache --> startcontainer
+    precompiledenabled2 -- no --> startcontainer
+```
+
+Once a wasm module or component is pre-compiled it will remain in the containerd content store until the original image is removed from containerd.  There is a small disk overhead associated with this but it reduces the complexity of managing stored versions during upgrades.
+
+To view the images in containerd that have associated pre-compilations:
+
+```bash
+sudo ctr i ls | grep "runwasi.io"
+ghcr.io/containerd/runwasi/wasi-demo-oci:latest                                                             application/vnd.oci.image.manifest.v1+json
+               sha256:60fccd77070dfeb682a1ebc742e9d677fc452b30a6b99188b081c968992394ce 2.4 MiB   wasi/wasm                                                                                                                           
+runwasi.io/precompiled/wasmtime/0.3.1=sha256:b36753ab5a46f26f6bedb81b8a7b489cede8fc7386f1398706782e225fd0a98e
+
+# query for the sha in the label
+sudo ctr content ls | grep "b36753ab5a46f26f6bedb81b8a7b489cede8fc7386f139870"
+sha256:60fccd77070dfeb682a1ebc742e9d677fc452b30a6b99188b081c968992394ce 561B    2 months        containerd.io/gc.ref.content.0=sha256:a3c18cd551d54d3cfbf67acc9e8f7ef5761e76827fe7c1ae163fca0193be88b3,containerd.io/gc.ref.content.config=sha256:85b7f2b562fe8665ec9d9e6d47ab0b24e2315627f5f558d298475c4038d71e8b,containerd.io/gc.ref.content.precompile=sha256:b36753ab5a46f26f6bedb81b8a7b489cede8fc7386f1398706782e225fd0a98e
+sha256:b36753ab5a46f26f6bedb81b8a7b489cede8fc7386f1398706782e225fd0a98e 626.4kB 3 days          runwasi.io/precompiled=sha256:60fccd77070dfeb682a1ebc742e9d677fc452b30a6b99188b081c968992394ce
+```