Re: when does btrfs create sparse extents?

[Marek Behun <marek.behun@nic.cz>]

On Wed, 22 Apr 2020 14:44:46 -0600
Chris Murphy <lists@colorremedies.com> wrote:

> e.g. from a 10m file created with truncate on two Btrfs file systems
> 
> original holes format (default)
> 
>     item 6 key (257 EXTENT_DATA 0) itemoff 15768 itemsize 53
>         generation 7412 type 1 (regular)
>         extent data disk byte 0 nr 0
>         extent data offset 0 nr 10485760 ram 10485760
>         extent compression 0 (none)
> 
> On a file system with no-holes feature set, this item simply doesn't
> exist. I think basically it works by inference. Both kinds of files
> have size in the INODE_ITEM, e.g.
> 
>     item 4 key (257 INODE_ITEM 0) itemoff 32245 itemsize 160
>         generation 889509 transid 889509 size 10485760 nbytes 0
> 
> Sparse extents are explicitly stated in the original format with disk
> byte 0 in an EXTENT_DATA item; whereas in the newer format, sparse
> extents exist whenever EXTENT_DATA items don't completely describe the
> file's size.

Ok this means that U-Boot currently gained support for the original
sparse extents.

I fear that current u-boot does not handle the new no-holes feature.