[PATCH v4 1/2] Kconfig: add btrfs to distro boot

[Tom Rini]

On Tue, Jan 28, 2020 at 11:26:25AM +0100, Matthias Brugger wrote:
> 
> 
> On 27/01/2020 22:58, Tom Rini wrote:
> > On Fri, Jan 17, 2020 at 08:59:02PM +0100, matthias.bgg at kernel.org wrote:
> > 
> >> From: Matthias Brugger <mbrugger at suse.com>
> >>
> >> Some distributions use btrfs as the default file system.
> >> Enable btrfs support by default when using distro boot for all
> >> architectures but riscv, as it breaks compilation due to size problems.
> >>
> >> Signed-off-by: Matthias Brugger <mbrugger at suse.com>
> > 
> > This adds around 60kb to many platforms, so I'm not going to take this
> > right now.  But I'm not rejecting it outright.  My question however is,
> > I was under the impression that the direction distributions were taking
> > was that bootefi would be used to start GRUB2 and that (and its
> > filesystem modules) would be responsible for doing the next steps.  So
> > we wouldn't need btrfs support here for example as everything would be
> > picked out of the system partition, which is FAT32.   Am I mistaken
> > about the flow here?  Thanks!
> > 
> 
> I think the assumption is correct for most of the distributions (if not all).
> However in distro boot we support e.g. extlinux/sysboot which not necessarily
> boots a EFI binary. Apart from that, think about a broken system partition. In
> that case if your distribution has the kernel on a btrfs partition, you would
> not be able to boot this kernel.
> That's the reason why we enable ext2 and ext4 support in distro boot.
> 
> Regarding the size, I'm aware of the problem, that's why it is set as imply in
> Kconfig so that individual boards can turn it off. We might think about chaning
> ext2 and ext4 from select to imply as well as we are at the limit on some platforms.

The extN support portion I thought predates bootefi+GRUB being
viable/common and is for when /boot was/is formatted as such.

My concern here (similar to my concern about distro boot + SPI) is that
we encourage the default for all boards to be "use distro boot, it makes
life easy on users".  Both big name distributions support it as well as
embedded oriented distributions.  Non-Linux supports it.  So growth here
is very important to consider.

Perhaps what we can talk about, for v2020.07, is a new not-default
sub-option of DISTRO_DEFAULTS to make it more robust, as in your
use-case and select more filesystems.  And move EXT2/EXT4 to that, but
also make all existing users keep it enabled (which is a little tricky,
but doable of a migration) and add BTRFS.  We can even see if it makes
sense to add ZFS there too for the BSD folks.

-- 
Tom
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