Re: btrfs-convert aborts with an assert

[David Sterba <dsterba@suse.cz>]

On Mon, Jun 06, 2022 at 04:03:33PM +0200, Torbjörn Jansson wrote:
> Hello
> 
> i tried to do a btrfs-convert of a ext4 filesystem and after a short while 
> after starting it i was greeted with:
> 
> # btrfs-convert /dev/xxxx
> btrfs-convert from btrfs-progs v5.16.2
> 
> convert/main.c:1162: do_convert: Assertion `cctx.total_bytes != 0` failed, value 0
> btrfs-convert(+0xffb0)[0x557defdabfb0]
> btrfs-convert(main+0x6c5)[0x557defdaa125]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xea)[0x7f66e1f8bd0a]
> btrfs-convert(_start+0x2a)[0x557defdab52a]
> Aborted

Please open an issue on github, thanks.

> Any idea whats going on?
> Is it a known bug?
> Is the btrfs-progs that come with my dist too old?

Two versions back is not that old, but there are bugfixes in each
release, so it's better to stay up to date.

> FYI the ext4 filesystem is a bit large ~10tb of used data on it.

This looks similar to another issue that caused weird checksum errors
(but no problems during conversion).
https://github.com/kdave/btrfs-progs/issues/349 the common point here is
thatt it's 2TB and a multiple in your case.

> I assume the convert didn't even start in this case and nothing was modified on 
> the ext4 filesystem, correct? or?

Yeah, until the conversion is completely finished without errors, the
old ext4 is left intact and the new partial btrfs structures are not
recognized as a valid filesystem.