Re: Seed device is broken, again.

[David Sterba <dsterba@suse.cz>]

On Fri, Feb 25, 2022 at 06:08:20PM +0800, Qu Wenruo wrote:
> Hi,
> 
> The very basic seed device usage is broken again:
> 
> 	mkfs.btrfs -f $dev1 > /dev/null
> 	btrfstune -S 1 $dev1
> 	mount $dev1 $mnt
> 	btrfs dev add $dev2 $mnt
> 	umount $mnt
> 
> 
> I'm not sure how many guys are really using seed device.
> 
> But I see a lot of weird operations, like calling a definite write 
> operation (device add) on a RO mounted fs.

That's how the seeding device works, in what way would you want to do
the ro->rw change?

> Can we make at least the seed sprouting part into btrfs-progs instead?

How? What do you mean? This is an in kernel operation that is done on a
mounted filesystem, progs can't do that.

> And can seed device even support the upcoming extent-tree-v2?

I should, it operates on the device level.

> Personally speaking I prefer to mark seed device deprecated completely.

If we did that with every feature some developer does not like we'd have
nothing left you know. Seeding is a documented usecase, as long as it
works it's fine to have it available.

> The call trace:
> 
>   assertion failed: sb_write_started(fs_info->sb), in 
> fs/btrfs/volumes.c:3244

Yeah the asserts now appear and we need to fix the write annotations
first. I've moved the patches out of misc-next again, it's now only in
for-next so it does not block testing.