[U-Boot] [PATCH v2 2/2] RISCV: image: Parse Image.gz support in booti.

[Atish Patra]

On 4/30/19 2:52 AM, Marek Vasut wrote:
> On 4/30/19 3:27 AM, Atish Patra wrote:
> 
> [...]
> 
>>>> Yes. FIT image parsing can be done in that way. However, the idea was
>>>> here to load Image.gz directly. Image.gz is default compressed Linux
>>>> kernel image format in RISC-V.
>>>
>>> Sigh, and the image header is compressed as well, so there's no way to
>>> identify the image format, right ? And there's no decompressor, so the
>>> dcompressing has to be done by bootloader, which would need some sort of
>>> very smart way of figuring out which exact compression method is used ?
>>>
>> Yes. Image.gz is always gunzip. So checking first two bytes is enough to
>> confirm that it is a gz file.
> 
> What happens once people start feeding it more exotic compression
> methods, like LZ4 or LZO or LZMA for example ?
> 

booti command help will clearly state that it can only boot kernel from 
Image or Image.gz.

static char booti_help_text[] =
  	"[addr [initrd[:size]] [fdt]]\n"
-	"    - boot arm64 Linux Image stored in memory\n"
+	"    - boot arm64 Linux Image or riscv Linux Image/Image.gz stored in 
memory\n"

(I will update the help text with Image.gz part)

Anything other than that, it will fail with following error.

"Bad Linux RISCV Image magic!"

>> The tricky part is length of the compressed file. I took another look at
>> the gunzip implementation in U-Boot. It looks like to me that compressed
>> header length just to parse the header correctly. It doesn't actually
>> use the "length" to decompress. In fact, it updates the length with
>> uncompressed bytes after the decompression.
> 
> That's possible.
> 

David suggested a better idea.

1. User can supply kernel_size and we can store in environment variable.
2. If the size is empty or greater than CONFIG_SYS_BOOTM_LEN, booti 
fails with appropriate error message.

We will update the documents to add the additional step for Image.gz

I am fine with either approach. Any preference ?

Regards,
Atish