Re: [PATCH] fs: btrfs: prevent unintentional int overflow

[Cengiz Can <cengiz@kernel.wtf>]

Hello David!

On 2020-01-07 19:01, David Sterba wrote:
> It's not a runtime overhead but typecasts should not be needed in
> general and when there's one it should be there for a reason. Sometimes
> it's apparent and does not need a comment to explain why but otherwise 
> I
> see it as "overhead" when reading the code. Lots of calculations done 
> in
> btrfs fit perfectly to 32bit, eg. the b-tree node or page-related ones.
> Where it matters is eg. conversion from/to bio::bi_sector to/from btrfs
> logical addresses that are u64, where the interface type is unsigned
> long and not a fixed width.

Thanks for sharing that. As I said, I'm relatively new to btrfs 
internals.

> The size constraints of the variables used in the reported expression
> are known to developers so I tend to think the typecast is not
> necessary.

Agreed.

> Maybe the static checker tool could be improved to know the
> invariants, that are eg. verified in fs/btrfs/disk-io.c:validate_super.

That's something that I will do some research on.

We can ignore this patch.

Thank you!

-- 
Cengiz Can
@cengiz_io