Partitioning SD cards

Partitioning SD cards

[Andy Pont]

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Hello,

I am working on a custom platform where U-Boot will be programmed into 
an SPI NOR flash device and the ext4 file systems will be in a removable 
microSD card.  The Linux kernel itself will be stored in the /boot 
directory of the root file system.

The customer wants the (16GB) microSD card formatted as 1GB to mount at 
/ and the remaining 15GB mounted as /home.

In the recipe for my image I have defined the following to try to create 
a suitable image for writing to the microSD card:

IMAGE_FSTYPES_append = " wic"
IMAGE_ROOTFS_SIZE = “1048576”

The image file that is being created is bigger than 1GB even though the 
root file system is only a little over 450MB.  Looking at the contents 
of what gets written to the microSD card this looks as though it is, in 
part, because it also includes the ~20MB “boot” partition containing the 
boot files.

A couple of questions…

How do I stop the wic generation process including the FAT formatted 
“boot” partition?

What is the best strategy for partitioning / formatting / mounting the 
second partition as /home?  Should it be part of the image build process 
or a one-time task run at first boot?

-Andy.



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Re: Partitioning SD cards

[Maciej Pijanowski]

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On 14.10.2019 14:13, Andy Pont wrote:
> Hello,
>
> I am working on a custom platform where U-Boot will be programmed into
> an SPI NOR flash device and the ext4 file systems will be in a
> removable microSD card.  The Linux kernel itself will be stored in the
> /boot directory of the root file system.
>
> The customer wants the (16GB) microSD card formatted as 1GB to mount
> at / and the remaining 15GB mounted as /home.
>
> In the recipe for my image I have defined the following to try to
> create a suitable image for writing to the microSD card:
>
> IMAGE_FSTYPES_append = " wic"
> IMAGE_ROOTFS_SIZE = “1048576”
>
> The image file that is being created is bigger than 1GB even though
> the root file system is only a little over 450MB.  Looking at the
> contents of what gets written to the microSD card this looks as though
> it is, in part, because it also includes the ~20MB “boot” partition
> containing the boot files.
>
> A couple of questions…
>
> How do I stop the wic generation process including the FAT formatted
> “boot” partition?
This depends on the wic (.wks) file you are using.
>
> What is the best strategy for partitioning / formatting / mounting the
> second partition as /home?  Should it be part of the image build
> process or a one-time task run at first boot?
Use --exclude-path and --rootfs-dir flags in the .wks file.
You can look at my example, where I extract one subdir from rootfs
(/storage in this case) on a separate partition.
https://github.com/3mdeb/meta-rte/blob/master/wic/sunxi-mmc-spl.wks

The rootfs parts should be named somewhere, like in distro config:
https://github.com/3mdeb/meta-rte/blob/master/conf/distro/rte.conf#L50
>
> -Andy.
>
>
>
-- 
Maciej Pijanowski
Embedded Systems Engineer
GPG: F1401D2E1CCB19EF
https://3mdeb.com | @3mdeb_com


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Re: Partitioning SD cards

[Andy Pont]

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Maciej wrote...

>>How do I stop the wic generation process including the FAT formatted 
>>“boot” partition?
>This depends on the wic (.wks) file you are using.
I have been using the default one (sdimage-bootpart.wks)?

>>What is the best strategy for partitioning / formatting / mounting the 
>>second partition as /home?  Should it be part of the image build 
>>process or a one-time task run at first boot?
>Use --exclude-path and --rootfs-dir flags in the .wks file.
>You can look at my example, where I extract one subdir from rootfs 
>(/storage in this case) on a separate partition.
>https://github.com/3mdeb/meta-rte/blob/master/wic/sunxi-mmc-spl.wks
I have created a “wic” directory in my custom layer and copied 
sdimage-bootpart.wks into it as sdimage-project.wks without making any 
changes but “wic list image” throws an error with the new .wks file:

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb0 in position 37: 
invalid start byte

-Andy.

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Re: Partitioning SD cards

[Andy Pont]

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I wrote...

>I have created a “wic” directory in my custom layer and copied 
>sdimage-bootpart.wks into it as sdimage-project.wks without making any 
>changes but “wic list image” throws an error with the new .wks file:
>
>UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb0 in position 
>37: invalid start byte
Ignore that, I deleted the directory and tried again and it is OK now!

-Andy.


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