Question re. <linux/sizes.h> required since btrfs-progs-4.10

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

Hi,

I'm on Gentoo and wanted to update Docker to 17.03.0, which failed when it
couldn't build the btrfs driver due to a missing <linux/sizes.h>.
This worked fine on another machine the other day, so I dug in and found that
the only difference was an intermediate update to btrfs-progs 4.10.
Sure enough: since 4.10 ctree.h includes <linux/sizes.h>, which is nowhere
to be found in my package of linux-headers-4.10 (also not in 4.9).

Simply copying sizes.h from the 4.9 kernel sources made everything work,
but I'm curious whether this is actually correct - hence my question whether
<linux/sizes.h> _should_ actually be installed? Is this a bug with
Gentoo's kernel header package or a new problem with btrfs-progs?

I don't see any good reason why sizes.h should not be installed, but wanted
to verify since there are probably users of other distributions here as
well. :)

Thanks,
Holger