container: Add --write-commitid-to for image deploy

Right now in coreos-assembler we have code that wants to know
the exact deploy root, and for that with layered images we need
the merge commit ID.

First, change the deploy API to return the image state.  There's
no reason to just throw it away.

Add an option to the CLI which writes the commitid to a file.

lib/src/cli.rs

@@ -5,7 +5,8 @@
 //! also exported as a library too, so that projects
 //! such as `rpm-ostree` can directly reuse it.
 
-use anyhow::Result;
+use anyhow::{Context, Result};
+use camino::Utf8PathBuf;
 use futures_util::FutureExt;
 use ostree::{cap_std, gio, glib};
 use std::borrow::Borrow;
@@ -247,6 +248,10 @@ enum ContainerImageOpts {
         #[structopt(long)]
         /// Add a kernel argument
         karg: Option<Vec<String>>,
+
+        /// Write the deployed checksum to this file
+        #[structopt(long)]
+        write_commitid_to: Option<Utf8PathBuf>,
     },
 }
 
@@ -632,6 +637,7 @@ where
                     target_imgref,
                     karg,
                     proxyopts,
+                    write_commitid_to,
                 } => {
                     let sysroot = &ostree::Sysroot::new(Some(&gio::File::for_path(&sysroot)));
                     sysroot.load(gio::NONE_CANCELLABLE)?;
@@ -645,8 +651,18 @@ where
                         target_imgref: target_imgref.as_ref(),
                         proxy_cfg: Some(proxyopts.into()),
                     };
-                    crate::container::deploy::deploy(sysroot, &stateroot, &imgref, Some(options))
-                        .await
+                    let state = crate::container::deploy::deploy(
+                        sysroot,
+                        &stateroot,
+                        &imgref,
+                        Some(options),
+                    )
+                    .await?;
+                    if let Some(p) = write_commitid_to {
+                        std::fs::write(&p, state.merge_commit.as_bytes())
+                            .with_context(|| format!("Failed to write commitid to {}", p))?;
+                    }
+                    Ok(())
                 }
             },
         },

lib/src/container/deploy.rs

@@ -1,5 +1,6 @@
 //! Perform initial setup for a container image based system root
 
+use super::store::LayeredImageState;
 use super::OstreeImageReference;
 use crate::container::store::PrepareResult;
 use anyhow::Result;
@@ -37,7 +38,7 @@ pub async fn deploy(
     stateroot: &str,
     imgref: &OstreeImageReference,
     options: Option<DeployOpts<'_>>,
-) -> Result<()> {
+) -> Result<Box<LayeredImageState>> {
     let cancellable = ostree::gio::NONE_CANCELLABLE;
     let options = options.unwrap_or_default();
     let repo = &sysroot.repo().unwrap();
@@ -66,5 +67,6 @@ pub async fn deploy(
     let flags = ostree::SysrootSimpleWriteDeploymentFlags::NONE;
     sysroot.simple_write_deployment(Some(stateroot), deployment, None, flags, cancellable)?;
     sysroot.cleanup(cancellable)?;
-    Ok(())
+
+    Ok(state)
 }