Add SparseOutput= setting to convert disk images to Android sparse format

mkosi/__init__.py

@@ -2779,6 +2779,9 @@ def check_inputs(config: Config) -> None:
             ),
         )
 
+    if config.sparse_output and config.output_format != OutputFormat.disk:
+        die("SparseOutput=yes can only be used with Format=disk")
+
     if config.is_incremental() and config.cacheonly == Cacheonly.never:
         die("Incremental=yes cannot be used with CacheOnly=never")
 
@@ -4186,6 +4189,24 @@ def build_image(context: Context) -> None:
                 f"Can't change the output size because the image is already larger ({format_bytes(current_size)}) than requested"  # noqa: E501
             )
 
+    if context.config.sparse_output:
+        if not context.config.find_binary("img2simg"):
+            die("SparseOutput=yes was requested but img2simg was not found")
+
+        output = context.staging / context.config.output_with_format
+
+        with complete_step("Converting disk image to Android sparse image…"):
+            tmp = output.parent / f"{output.name}.tmp"
+            run(
+                ["img2simg", workdir(output), workdir(tmp)],
+                sandbox=context.sandbox(
+                    options=[
+                        "--bind", context.staging, workdir(context.staging),
+                    ],
+                ),
+            )
+            tmp.rename(output)
+
     if context.config.output_format.use_outer_compression():
         maybe_compress(
             context,
@@ -4305,6 +4326,8 @@ def run_shell(args: Args, config: Config) -> None:
         die(f"Cannot {opname} {config.output_format} images with systemd-nspawn")
     if config.output_format.use_outer_compression() and config.compress_output:
         die(f"Cannot {opname} compressed {config.output_format} images with systemd-nspawn")
+    if config.sparse_output:
+        die(f"Cannot {opname} sparse images with systemd-nspawn")
 
     cmdline: list[PathString] = ["systemd-nspawn", "--quiet", "--link-journal=no", "--suppress-sync=yes"]
 

mkosi/config.py

@@ -2101,6 +2101,7 @@ class Config:
     sysupdate_dir: Optional[Path]
     sector_size: Optional[int]
     overlay: bool
+    sparse_output: bool
     seed: uuid.UUID
     el_torito: ConfigFeature
     el_torito_system: Optional[str]
@@ -3031,6 +3032,13 @@ def parse_kernel_module_filter_regexp(p: str) -> str:
         parse=config_parse_boolean,
         help="Only output the additions on top of the given base trees",
     ),
+    ConfigSetting(
+        dest="sparse_output",
+        metavar="BOOL",
+        section="Output",
+        parse=config_parse_boolean,
+        help="Convert the disk image to Android sparse format",
+    ),
     ConfigSetting(
         dest="seed",
         metavar="UUID",
@@ -5808,6 +5816,7 @@ def summary(config: Config) -> str:
                  Repart Directories: {line_join_list(config.repart_dirs)}
                         Sector Size: {none_to_default(config.sector_size)}
                             Overlay: {yes_no(config.overlay)}
+                      Sparse Output: {yes_no(config.sparse_output)}
                                Seed: {none_to_random(config.seed)}
                           El Torito: {config.el_torito}
                    El Torito System: {none_to_none(config.el_torito_system)}

mkosi/qemu.py

@@ -902,6 +902,8 @@ def run_qemu(args: Args, config: Config) -> None:
         OutputFormat.directory,
     ):
         die(f"{config.output_format} images cannot be booted in qemu")
+    if config.sparse_output:
+        die("Sparse images cannot be booted in qemu")
 
     if (
         config.output_format in (OutputFormat.cpio, OutputFormat.uki, OutputFormat.esp)

mkosi/resources/man/mkosi.1.md

@@ -790,6 +790,12 @@ boolean argument: either `1`, `yes`, or `true` to enable, or `0`, `no`,
 
     This option may be used to create [systemd *system extensions*](https://uapi-group.org/specifications/specs/extension_image).
 
+`SparseOutput=`, `--sparse-output=`
+:   Takes a boolean value. If enabled, the output disk image is converted
+    to Android sparse format using **img2simg**. This is useful for flashing
+    images via **fastboot**. Can only be used with `Format=disk`. Defaults
+    to `no`.
+
 `Seed=`, `--seed=`
 :   Takes a UUID as argument or the special value `random`.
     Overrides the seed that **systemd-repart**

mkosi/vmspawn.py

@@ -41,6 +41,8 @@ def run_vmspawn(args: Args, config: Config) -> None:
         OutputFormat.uki,
     ):
         die(f"{config.output_format} images cannot be booted in systemd-vmspawn")
+    if config.sparse_output:
+        die("Sparse images cannot be booted in systemd-vmspawn")
 
     kernel = config.expand_linux_specifiers() if config.linux else None
     firmware = finalize_firmware(config, kernel)