BlobCopy

Copies specific files (firmware blobs, binaries, libraries) from block device partitions to the local filesystem. Handles device readiness, mounting, manifest-driven file copying, and marker-based idempotency.

Designed for embedded Linux systems (e.g. Nerves) where firmware blobs or vendor files need to be copied from a dedicated partition at boot time.

Features

• Idempotent -- uses a marker file so the copy is a no-op on subsequent boots
• Manifest-driven -- declaratively specify which files to copy, with glob support
• Resilient -- waits for block devices to appear and retries mounts, handling early-boot timing issues
• Partial failure tolerance -- non-critical entries can fail without blocking the operation; only critical: true entries cause overall failure
• Read-only mounting -- source partition is always mounted read-only
• Zero runtime dependencies -- pure Elixir library

Installation

Add blob_copy to your list of dependencies in mix.exs:

def deps do
  [
    {:blob_copy, "~> 0.1.0"}
  ]
end

Usage

Basic example

config = %BlobCopy.Config{
  partition: "/dev/mmcblk0p10",
  mount_point: "/tmp/vendor-mount",
  marker_file: "/var/lib/blob-copy-done",
  manifest: [
    %{source: "lib/firmware", dest: "/lib/firmware"},
    %{source: "usr/bin/tool", dest: "/usr/bin/tool", critical: true},
    %{source: "etc/*config*", dest: "/etc"}
  ]
}

BlobCopy.ensure_copied(config)

From application config

# config/config.exs
config :my_app, :blob_copy,
  partition: "/dev/mmcblk0p10",
  mount_point: "/tmp/vendor-mount",
  marker_file: "/var/lib/blob-copy-done",
  manifest: [
    %{source: "lib/firmware", dest: "/lib/firmware", critical: true}
  ]

# In your application code
Application.fetch_env!(:my_app, :blob_copy)
|> BlobCopy.Config.new!()
|> BlobCopy.ensure_copied()

Configuration

BlobCopy.Config accepts the following fields:

Field	Type	Required	Default	Description
partition	string	yes	--	Block device path (e.g. "/dev/mmcblk0p10")
mount_point	string	yes	--	Temporary mount point path
marker_file	string	yes	--	Path to idempotency marker file
manifest	list	yes	--	List of file entries to copy
log_prefix	string	no	"BlobCopy"	Prefix for log messages
partition_wait_timeout	integer	no	30_000	Ms to wait for the block device to appear
mount_retries	integer	no	10	Number of mount retry attempts
mount_retry_delay	integer	no	1_000	Ms between mount retries

Manifest entries

Each manifest entry is a map with:

Field	Type	Required	Default	Description
source	string	yes	--	Path relative to mount point; may contain glob characters (*, ?, [)
dest	string	yes	--	Absolute destination path
permissions	integer	no	0o755	File permissions (ignored for directory copies)
critical	boolean	no	false	If true, failure to copy this entry fails the entire operation

The copy mode is auto-detected per entry:

• Glob -- source contains *, ?, or [: all matches are copied into dest
• Directory -- resolved source is a directory: copied recursively
• File -- single file copy with permissions set

API

• BlobCopy.ensure_copied(%Config{}) -- idempotent copy operation. Returns :ok or {:error, reason}.
• BlobCopy.copied?(%Config{}) -- returns true if the marker file exists.

Requirements

• Linux -- uses mount, umount, mountpoint, cp, and reads /proc/mounts
• Root privileges (or appropriate capabilities) for mount/unmount operations
• Elixir >= 1.14

Development

mix deps.get
mix compile
mix docs    # generate documentation
mix test    # run tests

License

MIT -- see LICENSE for details.