[PATCH v4 2/8] doc: Add gpt command documentation

Heinrich Schuchardt xypron.glpk at gmx.de
Tue Aug 29 00:59:51 CEST 2023 

On 8/29/23 00:45, Heinrich Schuchardt wrote:
> /On 8/28/23 23:56, Joshua Watt wrote:
>> Adds initial documentation for the gpt command
>>
>> Signed-off-by: Joshua Watt <JPEWhacker at gmail.com>
>> ---
>>   doc/usage/cmd/gpt.rst | 184 ++++++++++++++++++++++++++++++++++++++++++
>>   doc/usage/index.rst   |   1 +
>>   2 files changed, 185 insertions(+)
>>   create mode 100644 doc/usage/cmd/gpt.rst
>>
>> diff --git a/doc/usage/cmd/gpt.rst b/doc/usage/cmd/gpt.rst
>> new file mode 100644
>> index 0000000000..6387c8116f
>> --- /dev/null
>> +++ b/doc/usage/cmd/gpt.rst
>> @@ -0,0 +1,184 @@
>> +.. SPDX-License-Identifier: GPL-2.0+
>> +
>> +gpt command
>> +===========
>> +
>> +Synopsis
>> +--------
>> +
>> +::
>> +
>> +    gpt enumerate <interface> <dev>
>> +    gpt guid <interface> <dev> [<varname>]
>> +    gpt read <interface> <dev> [<varname>]
>> +    gpt rename <interface> <dev> <part> <name>
>> +    gpt repair <interface> <dev>
>> +    gpt setenv <interface> <dev> <partition name>
>> +    gpt swap <interface> <dev> <name1> <name2>
>> +    gpt verify <interface> <dev> [<partition string>]
>> +    gpt write <interface> <dev> <partition string>
>> +
>> +Description
>> +-----------
>> +
>> +The gpt command lets users read, create, modify, or verify the GPT (GUID
>> +Partition Table) partition layout.
>> +
>> +Common arguments:
>> +
>> +interface
>> +    interface for accessing the block device (mmc, sata, scsi, usb,
>> ....)
>> +
>> +dev
>> +    device number
>> +
>> +partition string
>> +    Describes the GPT partition layout for a disk.  The syntax is
>> similar to
>> +    the one used by the :doc:`mbr command <mbr>` command. The string
>> contains
>> +    one or more partition descriptors, each separated by a ";". Each
>> descriptor
>> +    contains one or more fields, with each field separated by a ",".
>> Fields are
>> +    either of the form "key=value" to set a specific value, or simple
>> "flag" to
>> +    set a boolean flag
>> +
>> +    The first descriptor can optionally be used to describe
>> parameters for the
>> +    whole disk with the following fields:
>> +
>> +    * uuid_disk=UUID - Set the UUID for the disk
>> +
>> +    Partition descriptors can have the following fields:
>> +
>> +    * name=<NAME> - The partition name, required
>> +    * start=<BYTES> - The partition start offset in bytes, required
>
> The code has this comment: "start address is optional".
>
>> +    * size=<BYTES> - The partition size in bytes or "-" to expand it
>> to the whole free area
>
> This filed is mandatory.
>
>> +    * bootable - Set the legacy bootable flag
>
> This field is optional
>
>> +    * uuid=<UUID> - The partition UUID, optional if
>> CONFIG_RANDOM_UUID=y is enabled
>> +    * type=<UUID> - The partition type GUID, requires
>> CONFIG_PARTITION_TYPE_GUID=y
>
> This field is optional
>
> Thanks for all the updates. Looks much neater now.
>
> The sequence expected in set_gpt_info() is:
>
> uuid (optional if CONFIG_RANDOM_UUID=y),
> type (optional, only usable for CONFIG_PARTITION_TYPE_GUID=y),
> name (mandatory),
> size (mandatory),
> start (optional),
> bootable (optional).

A gross bug in the gpt command is that 'gpt read' creates a different
sequence than 'gpt write' needs.

Furthermore 'gpt read' does not write all fields needed by 'gpt write'
to recreate the partition table: bootable and type are missing.

Best regards

Heinrich

>
>  From the description above it is not clear that:
>
> * semicolons are used to separate partitions
> * the exact sequence of fields must be kept
> * commas are used to separate fields
> * no extra white-space is allowed.
>
>> +
>> +
>> +    If 'uuid' is not specified, but CONFIG_RANDOM_UUID is enabled, a
>> random UUID
>> +    will be generated for the partition
>> +
>> +gpt enumerate
>> +~~~~~~~~~~~~~
>> +
>> +Sets the variable 'gpt_partition_list' to be a list of all the
>> partition names
>> +on the device.
>> +
>> +gpt guid
>> +~~~~~~~~
>> +
>> +Report the GUID of a disk. If 'varname' is specified, the command
>> will set the
>> +variable to the GUID, otherwise it will be printed out.
>> +
>> +gpt read
>> +~~~~~~~~
>> +
>> +Prints the current state of the GPT partition table. If 'varname' is
>> specified,
>> +the variable will be filled with a partition string in the same
>> format as a
>> +'<partition string>', suitable for passing to other 'gpt' commands.
>> If the
>> +argument is omitted, a human readable description is printed out.
>> +CONFIG_CMD_GPT_RENAME=y is required.
>> +
>> +gpt rename
>> +~~~~~~~~~~
>> +
>> +Renames all partitions named 'part' to be 'name'.
>> CONFIG_CMD_GPT_RENAME=y is
>> +required.
>> +
>> +gpt repair
>> +~~~~~~~~~~
>> +
>> +Repairs the GPT partition tables if it they become corrupted.
>> +
>> +gpt setenv
>> +~~~~~~~~~~
>> +
>> +The 'gpt setenv' command will set a series of environment variables with
>> +information about the partition named '<partition name>'. The
>> variables are:
>> +
>> +gpt_partition_addr
>> +    the starting offset of the partition in blocks as a hexadecimal
>> number
>> +
>> +gpt_partition_size
>> +    the size of the partition in blocks as a hexadecimal number
>> +
>> +gpt_partition_name
>> +    the name of the partition
>> +
>> +gpt_partition_entry
>> +    the partition number in the table, e.g. 1, 2, 3, etc.
>
> Since eeef58401520 ("cmd: let gpt_partition_entry be hexadecimal") this
> is a hexadecimal number. As partitions are not required to be numbered
> start at 1:
>
> %s/, e.g. 1, 2, 3, etc./as a hexadecimal number/
>
>> +
>> +gpt swap
>> +~~~~~~~~
>> +
>> +Changes the names of all partitions that are named 'name1' to be
>> 'name2', and
>> +all partitions named 'name2' to be 'name1'. CONFIG_CMD_GPT_RENAME=y is
>> +required.
>> +
>> +gpt verify
>> +~~~~~~~~~~
>> +
>> +Sets return value $? to 0 (true) if the partition layout on the
>> +specified disk matches the one in the provided partition string, and
>> 1 (false)
>> +if it does not match. If no partition string is specified, the
>> command will
>> +check if the disk is partitioned or not.
>> +
>> +gpt write
>> +~~~~~~~~~
>> +
>> +(Re)writes the partition table on the disk to match the provided
>> +partition string. It returns 0 on success or 1 on failure.
>> +
>> +Configuration
>> +-------------
>
> All other man-pages have Configuration after Examples.
>
>> +
>> +To use the 'gpt' command you must specify CONFIG_CMD_GPT=y. To enable
>> 'gpt
>> +read', 'gpt swap' and 'gpt rename', you must specify
>> CONFIG_CMD_GPT_RENAME=y.
>> +
>> +Examples
>> +~~~~~~~~
>
> An example for gpt read would be nice.
>
>> +Create 6 partitions on a disk:: > +
>> +    => setenv gpt_parts 'uuid_disk=bec9fc2a-86c1-483d-8a0e-0109732277d7;
>> +
>> name=boot,start=4M,size=128M,bootable,type=ebd0a0a2-b9e5-4433-87c0-68b6b72699c7,
>> +
>> name=rootfs,size=3072M,type=0fc63daf-8483-4772-8e79-3d69d8477de4;
>> +
>> name=system-data,size=512M,type=0fc63daf-8483-4772-8e79-3d69d8477de4;
>> +        name=[ext],size=-,type=0fc63daf-8483-4772-8e79-3d69d8477de4;
>> +        name=user,size=-,type=0fc63daf-8483-4772-8e79-3d69d8477de4;
>> +
>> name=modules,size=100M,type=0fc63daf-8483-4772-8e79-3d69d8477de4;
>> +        name=ramdisk,size=8M,type=0fc63daf-8483-4772-8e79-3d69d8477de4
>> +    => gpt write mmc 0 $gpt_parts
>
> There is a starting single quotation mark, but I don't see an ending
> single quotation mark.
>
> White-space is not allowed before 'name='. As ugly as it is, please, put
> the whole setenv command into a single line.
>
> You cannot use a comma before name=. It must be a semicolon.
>
> Looking at the code the sequence in the partition descriptors seems to
> be wrong. It should be
>
> uuid (optional if CONFIG_RANDOM_UUID=y),
> type (optional, only usable for CONFIG_PARTITION_TYPE_GUID=y),
> name (mandatory),
> size (mandatory),
> start (optional),
> bootable (optional).
> .
> Please, use a command that you have actually tested and copy it
> verbatim. sandbox_defconfig has a host bind command to attach a file as
> drive. That makes testing easy.
>
>> +
>> +
>> +Verify that the device matches the partition layout described in the
>> variable
>> +$gpt_parts::
>> +
>> +    => gpt verify mmc 0 $gpt_parts
>
> How about adding output here:
>
> => gpt verify mmc 0 $gpt_parts; echo $?
> 0
>
> Best regards
>
> Heinrich
>
>> +
>> +
>> +Get the information about the partition named 'rootfs'::
>> +
>> +    => gpt setenv mmc 0 rootfs
>> +    => echo ${gpt_partition_addr}
>> +    2000
>> +    => echo ${gpt_partition_size}
>> +    14a000
>> +    => echo ${gpt_partition_name}
>> +    rootfs
>> +    => echo ${gpt_partition_entry}
>> +    2
>> +
>> +Get the list of partition names on the disk::
>> +
>> +    => gpt enumerate
>> +    => echo gpt_partition_list
>> +    boot rootfs system-data [ext] user modules ramdisk
>> +
>> +
>> +Get the GUID for a disk::
>> +
>> +    => gpt guid mmc 0
>> +    bec9fc2a-86c1-483d-8a0e-0109732277d7
>> +    => gpt guid mmc gpt_disk_uuid
>> +    => echo ${gpt_disk_uuid}
>> +    bec9fc2a-86c1-483d-8a0e-0109732277d7
>> diff --git a/doc/usage/index.rst b/doc/usage/index.rst
>> index f45a7f5502..fa702920fa 100644
>> --- a/doc/usage/index.rst
>> +++ b/doc/usage/index.rst
>> @@ -66,6 +66,7 @@ Shell commands
>>      cmd/for
>>      cmd/fwu_mdata
>>      cmd/gpio
>> +   cmd/gpt
>>      cmd/host
>>      cmd/imxtract
>>      cmd/load
>

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