Per region file arguments

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Current chromium impl.

Current chromium flashrom implements the syntax like this:

   [-i <region>[:<file>]]... -r|-w|-v [<filename>]

Where <filename> can be given anywhere on the command line (non-positional, matching legacy flashrom behavior)

The syntax has been in use since 2011 to optimize flashrom for manufacturing and time-sensitive use cases (OS boot/resume/suspend paths). It is deployed on all ChromeOS devices and used during manufacturing of ChromeOS devices, so it has a long history of usage even though the syntax has not yet been adopted upstream.

Rules:

  • Argument to -r/-w/-v is optional.
    • If used, it tells flashrom to operate on a ROM-sized file.
    • If not, flashrom will only operate on region-sized files specified in -i arguments.
  • If no argument to -r/-w/-v is specified, then files must be specified via -i arguments.
  • -r/-w/-v and -i options are non-positional, allowing commands to be easily constructed dynamically by higher-level logic.
  • For reading:
    • If -i region:<file> is used, read content from region into <file>.
    • If any -i region:<file> is specified along with -r <filename>, read all included regions into <filename> and all included regions with a <file> specified into the respective file
  • For writing and verifying:
    • If -i region:<file> is used, write content from <file> to region or verify content from <file> against region.
    • If any -i region:<file> is specified along with -w <filename>, the data of -i region:<file> will overwrite data in <filename>. This is useful for patching specific regions of a generic image, for example if you have a release image for a platform and wish to patch it with machine-specific data (such as MAC address) at manufacturing time.
    • Regions with files specified via -i region:<file> must not overlap

More examples: https://www.chromium.org/chromium-os/packages/cros-flashrom#TOC-Partial-Reads-and-Writes

Alternative #1

   [-i <region>]... (-r|-w|-v [<region>:]<filename>)...

Easier to implement, no optional arguments, no non-positional arguments.

Rules for sanity:

  • combinations of -r/-w/-v are not allowed
  • -r/-w/-v <filename> (i.e. without a <region>) may only be specified once
  • if no -r/-w/-v <filename> (i.e. without a <region>) is specified, no -i arguments may be given either

optionally, stricter

Never mix <region>:<file> with the old -i syntax in one invocation:

   ([-i <region>]... (-r|-w|-v <filename>) | (-r|-w|-v <region>:<filename>)...)

Files not matching the region's size

Both syntaxes can be extended for files that are smaller than the region:

   <region>[<filename>

would denote that the file's contents should be placed at the start/bottom of the region,

   <region>]<filename>

that the file's contents should be placed at the end/top of the region. By default the uncovered part of the region should be kept as is, unless

   --pad

is specified, in which case the uncovered part would be padded with the flash chip's erased state (usually 0xff).

Additonal rules

  • Beside `:`, `[` and `]` wouldn't be allowed in region names.

Alternative #2

Deprecate `-i`, embed region into -r/-w/-v

   -r|-w|-v [<region>:]<filename>
  • No optional or non-positional arguments
  • Must err out if -r/-w/-v are mixed.
  • Cannot utilize regions and chip-sized files easily.
  • Erasing specific regions will be unsupported since -E does not take arguments.

Use cases

Operation CrOS syntax Alternative #1 Alternative #2 (deprecate `-i`)
Read entire chip into file flashrom -p prog -r file.bin flashrom -p prog -r file.bin flashrom -p prog -r file.bin
Read region(s) into chip-sized file flashrom -p prog -l layout -i region -r file.bin flashrom -p prog -l layout -i region -r file.bin n/a
Read region(s) into region-sized files flashrom -p prog -l layout -i region:region.bin -r flashrom -p prog -l layout -r region:region.bin flashrom -p prog -l layout -r region:region.bin
Read region(s) into region-sized files and into chip-sized file [1] flashrom -p prog -l layout -i region:region.bin -r file.bin flashrom -p prog -l layout -r region:region.bin -r file.bin flashrom -p prog -l layout -r region:region.bin -r file.bin
Write chip-sized file to chip flashrom -p prog -w file.bin flashrom -p prog -w file.bin flashrom -p prog -w file.bin
Write regions(s) from chip-sized file to chip flashrom -p prog -l layout -i region -w file.bin flashrom -p prog -l layout -i region -w file.bin n/a
Write region(s) from region-sized files to chip flashrom -p prog -l layout -i region:region.bin -w flashrom -p prog -l layout -w region:region.bin flashrom -p prog -l layout -w region:region.bin
Write chip-sized file while applying region-specific patches [2] flashrom -p prog -l layout -i region:region.bin -w file.bin flashrom -p prog -l layout -w region:region.bin -w file.bin flashrom -p prog -l layout -w region:region.bin -w file.bin
Verify using a chip-sized file flashrom -p prog -v file.bin flashrom -p prog -v file.bin flashrom -p prog -v file.bin
Verify regions using a chip-sized file flashrom -p prog -l layout -i region -v file.bin flashrom -p prog -l layout -i region -v file.bin n/a
Verify regions using region-sized files flashrom -p prog -l layout -i region:region.bin -v flashrom -p prog -l layout -v region:region.bin flashrom -p prog -l layout -v region:region.bin
Erase chip flashrom -p prog -E flashrom -p prog -E flashrom -p prog -E
Erase regions(s) flashrom -p prog -l layout -i region -E flashrom -p prog -l layout -i region -E (?) n/a

[1] This is a niche case used in some ChromeOS scripts that might not be necessary anymore.

[2] This is an optimization for when certain data is generated during manufacturing of the system and needs to be flashed to specific regions, e.g. ChromeOS VPD; In other words, this "patches" the base firmware image supplied to `-w` with data that may be generated dynamically.