Re: [PATCH v4 2/2] btrfs-progs: cmds: Add subcommand that dumps file extents

[Sidong Yang <realwakka@gmail.com>]

On Wed, Aug 18, 2021 at 06:59:24PM +0200, David Sterba wrote:
> On Wed, Aug 18, 2021 at 12:38:19AM +0000, Sidong Yang wrote:
> > On Tue, Aug 17, 2021 at 03:30:22PM +0200, David Sterba wrote:
> > > On Sun, Jul 18, 2021 at 06:46:01AM +0000, Sidong Yang wrote:
> > > > This patch adds an subcommand in inspect-internal. It dumps file extents of
> > > > the file that user provided. It helps to show the internal information
> > > > about file extents comprise the file.
> > > 
> > > Do you have an example of the output? That's the most interesting part.
> > > Thanks.
> > 
> > Thanks for reply.
> > This is an example of the output below.
> > 
> > # ./btrfs inspect-internal dump-file-extent /mnt/test1
> > type = regular, start = 2097152, len = 3227648, disk_bytenr = 0, disk_num_bytes = 0, offset = 0, compression = none
> > type = regular, start = 5324800, len = 16728064, disk_bytenr = 0, disk_num_bytes = 0, offset = 0, compression = none
> > type = regular, start = 22052864, len = 8486912, disk_bytenr = 0, disk_num_bytes = 0, offset = 0, compression = none
> > type = regular, start = 30572544, len = 36540416, disk_bytenr = 0, disk_num_bytes = 0, offset = 0, compression = none
> > type = regular, start = 67112960, len = 5299630080, disk_bytenr = 0, disk_num_bytes = 0, offset = 0, compression = none
> 
> This resembles a debugging output, something like we have for
> tracepoints but I think this should be more human readable, with
> possiblity of parsing by scripts/tools.

Yes, I agree. I think It would be text or json.
> 
> So to not just duplicate what filefrag or xfs_io -c fiemap do, we can
> optionally enhance the information with the specifics of btrfs, like on
> which devices the extents are, which compression is there etc. But the
> basic output should be more or less like filefrag.

Yeah, this is the limit for this patch. for more than filefrag or
xfs_io, it should provide more specifics. compression type is already
included. But it would be better that it describe which device 
has the extents. it goes to v2.