[U-Boot] [PATCH v3 3/7] gpt:doc: GPT (GUID Partition Table) documentation

[Stephen Warren]

On 09/13/2012 02:10 AM, Lukasz Majewski wrote:
> Documentation of the GPT format.

> diff --git a/doc/README.gpt b/doc/README.gpt

> +Example usage:
> +==============
> +
> +To restore GUID partition table one needs to:
> +1. at ./include/configs/{board}.h
> +   - define "partitions=" environment variable with format:
> +     "name=u-boot,size=60M;name=kernel,size=60M;name=platform,size=1G;"
> +   - define GPT_PARTS_NUM with actual number of partitions (as defined above)

That seems unfortunate; the partitions variable and GPT_PARTS_NUM define
could easily become out-of-sync (what if the user edited the variable in
order to create an alternative disk layout, or what if a developer
simply forgot to update GPT_PARTS_NUM when editing the hard-coded value?).

Instead, can't GPT_PARTS_NUM be removed, and the code simply count the
number of entries in the partitions variable?

> +   - #define CONFIG_EFI_PARTITION and #define CONFIG_CMD_GPT
> +
> +2. From u-boot prompt type:
> +   gpt mmc 0 uuid_disk=ec2cddf2-fbf5-11e1-af3a-001fd09285c0, \
> +   uuid1=ed09c4b0-fbf5-11e1-9a95-001fd09285c0, \
> +   uuid2=edd6d93c-fbf5-11e1-875a-001fd09285c0, \
> +   uuid3=f0485114-fbf5-11e1-a3ae-001fd09285c0 ...
> +
> +   UUIDs shall be defined up to GPT_PARTS_NUM. Smaller number is acceptable.
> +   When UUIDs are NOT provided, internal (rather weak) GUID generator will be
> +   used instead

Hmmm. It's a little unfortunate to provide the partitions list through
one mechanism (environment variable with a hard-coded name), and the
UUIDs through a different mechanism (command-line). Surely these two
mechanisms can be combined; rather than the command reading an
environment variable, you could at least require the user to pass the
appropriate data on the command-line, and optionally have them pass the
environment variable if they want to use the pre-defined layout, e.g.:

pre-defined:
gpt mmc 0 ${partitions}

manual/custom layout:
gpt mmc 0 name=u-boot,size=60M;name=kernel,size=60M;...

Then, I wonder if you couldn't define the partitions environment
variable as:

partitions=\
name=u-boot,size=60M,uuid=${uuid_gpt_u_boot};\
name=kernel,size=60M,uuid=${uuid_gpt_kernel};...

and have the environment variables expanded as in:

setenv uuid_gpt_u_boot=ed09c4b0-fbf5-11e1-9a95-001fd09285c0
setenv uuid_gpt_kernel=...
gpt mmc 0 ${partitions}

That way, the gpt command would read everything from the command-line,
yet the partition layout and UUID names could be specified separately,
so as to allow the user to define them at different times or places.

The implementation of "gpt" would have to scan all the variables it
extracted from the command-line, and expand any environment variable
references in them for this to work, since I assume the shell doesn't do
recursive variable expansions like make does.

Oh, and don't you want the "gpt" command to take a sub-command like
"create", so that "gpt" could do different things in the future, e.g.
take an existing GPT layout, and edit, say, one partition's name:

gpt create mmc 0 ${partitions}
gpt set-name mmc 0 ${partition-id} ${new-name}