cli/ota: Add support for extracting specific images

Previously, we only supported extracting all images or the subset of
images that could potentially be patched by avbroot. This was
unnecessarily slow if the user only needed to extract a specific image.

This commit also deprecates and hides the `--boot-only` option, though
the functionality will remain indefinitely.

Signed-off-by: Andrew Gunnerson <accounts+github@chiller3.com>

README.md

@@ -297,8 +297,7 @@ Magisk versions 25211 and newer require a writable partition for storing custom
     ```bash
     avbroot ota extract \
         --input /path/to/ota.zip \
-        --directory . \
-        --boot-only
+        --partition <name> # init_boot or boot, depending on device
     ```
 
 2. Patch the boot image via the Magisk app. This **MUST** be done on the target device or a device of the same model! The partition name will be incorrect if patched from Magisk on a different device model.

avbroot/src/cli/ota.rs

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: 2022-2024 Andrew Gunnerson
+// SPDX-FileCopyrightText: 2022-2025 Andrew Gunnerson
 // SPDX-License-Identifier: GPL-3.0-only
 
 use std::{
@@ -79,8 +79,9 @@ impl RequiredImages {
         let partitions = manifest
             .partitions
             .iter()
-            .map(|p| p.partition_name.clone())
+            .map(|p| &p.partition_name)
             .filter(|n| Self::is_boot(n) || Self::is_system(n) || Self::is_vbmeta(n))
+            .cloned()
             .collect();
 
         Self(partitions)
@@ -1437,7 +1438,7 @@ pub fn extract_subcommand(cli: &ExtractCli, cancel_signal: &AtomicBool) -> Resul
 
     let mut unique_images = BTreeSet::new();
 
-    if cli.all {
+    if cli.extract.all {
         unique_images.extend(
             header
                 .manifest
@@ -1446,10 +1447,31 @@ pub fn extract_subcommand(cli: &ExtractCli, cancel_signal: &AtomicBool) -> Resul
                 .map(|p| &p.partition_name)
                 .cloned(),
         );
+    } else if !cli.extract.partition.is_empty() {
+        // We check this later too, but also do it here so we don't create a
+        // bunch of empty files before failing.
+        let valid_images = header
+            .manifest
+            .partitions
+            .iter()
+            .map(|p| &p.partition_name)
+            .collect::<BTreeSet<_>>();
+        let missing_images = cli
+            .extract
+            .partition
+            .iter()
+            .filter(|p| !valid_images.contains(p))
+            .collect::<Vec<_>>();
+
+        if !missing_images.is_empty() {
+            bail!("Invalid partitions: {}", joined(missing_images));
+        }
+
+        unique_images.extend(cli.extract.partition.iter().cloned());
     } else {
         let images = RequiredImages::new(&header.manifest);
 
-        if cli.boot_only {
+        if cli.extract.boot_only {
             unique_images.extend(images.iter_boot().map(|n| n.to_owned()));
         } else {
             unique_images.extend(images.iter().map(|n| n.to_owned()));
@@ -1975,6 +1997,25 @@ pub struct PatchCli {
     pub boot_partition: Option<String>,
 }
 
+#[derive(Debug, Args)]
+#[group(multiple = false)]
+pub struct ExtractGroup {
+    /// Extract all images from the payload.
+    ///
+    /// By default, only images that could potentially be patched by avbroot are
+    /// extracted.
+    #[arg(short, long)]
+    pub all: bool,
+
+    /// (Deprecated: Specify an exact partition name instead.)
+    #[arg(long, hide = true)]
+    pub boot_only: bool,
+
+    /// Extract specific images from the payload.
+    #[arg(short, long)]
+    pub partition: Vec<String>,
+}
+
 /// Extract partition images from an OTA zip's payload.
 #[derive(Debug, Parser)]
 pub struct ExtractCli {
@@ -1986,13 +2027,8 @@ pub struct ExtractCli {
     #[arg(short, long, value_parser, default_value = ".")]
     pub directory: PathBuf,
 
-    /// Extract all images from the payload.
-    #[arg(short, long, group = "extract")]
-    pub all: bool,
-
-    /// Extract only the boot image.
-    #[arg(long, group = "extract")]
-    pub boot_only: bool,
+    #[command(flatten)]
+    pub extract: ExtractGroup,
 
     /// (Deprecated: no longer needed)
     #[arg(long, value_name = "PARTITION", hide = true)]