Re: [PATCH] fs: btrfs: fix reading when length specified

[Sam Edwards <cfsworks@gmail.com>]

On 11/15/23 21:43, Qu Wenruo wrote:
> 
> I'm not sure why this happend for the EFI environment.
> 
> Doesn't the EFI runtime should also try to read the whole file? Or that
> EFI environment has specified the length to read instead?
> 

Hi Qu,

The Linux EFISTUB file loading routine (handle_cmdline_files) reads 
files in chunks, and not (necessarily) the whole file in one go. On x86 
platforms, the chunk size is 1MB, and the comments explain that this is 
to work around firmware implementations that have problems with large 
reads. On non-x86 platforms, the chunk size is ULONG_MAX -- which in 
practice means it reads the whole file in one exact-filesize chunk.

So, to answer your questions: "either/both depending on platform."

(The bug in the U-Boot implementation doubtlessly affects more than just 
EFI; I only happened to discover it while trying to use EFI.)

>>
>> Signed-off-by: Sam Edwards <CFSworks@gmail.com>
> 
> Anyway, the fix looks good to me.
> 
> Reviewed-by: Qu Wenruo <wqu@suse.com>

Thank you greatly for the review!

> 
> Thanks,
> Qu

Likewise,
Sam