Re: booting btrfs

[Andrey Borzenkov]

В Mon, 14 Oct 2013 21:12:06 -0600
Chris Murphy <address@hidden> пишет:

> 
> So actually, this is a bit more than somewhat messy, whether the prefix 
> should be formatted relative to the default subvolume, or absolute from top 
> level 5 subvolume. It depends on the use case.
> 
> So just like '-o subvol=root' has a different meaning than '-o subvol=/root' 
> there is a difference between prefix=(hd0,msdos1)boot/grub/ and 
> prefix=(hd0,msdos1)/boot/grub/
> 

I do not know whether it was the case in the past, but today there is
*no* difference between using absolute or relative form. As I already
said, internally btrfs mounts top level and starts from there anyway.


linux-xtd6:/mnt # btrfs subvolume list /mnt
ID 256 gen 7 top level 5 path dir1/sub1
ID 257 gen 7 top level 5 path dir2/sub2
linux-xtd6:/mnt # btrfs subvolume get-default /mnt
ID 256 gen 7 top level 5 path dir1/sub1
linux-xtd6:~ # umount /mnt
linux-xtd6:~ # mount /dev/sdb /mnt
linux-xtd6:~ # ls -l /mnt
total 0
-rw-r--r-- 1 root root 0 Oct 15 16:50 I am subvolume 1
linux-xtd6:~ # umount /mnt
linux-xtd6:~ # mount -o subvol=/dir2/sub2 /dev/sdb /mnt
linux-xtd6:~ # ls -l /mnt
total 0
-rw-r--r-- 1 root root 0 Oct 15 16:50 I am subvolume 2
linux-xtd6:~ # umount /mnt
linux-xtd6:~ # mount -o subvol=dir2/sub2 /dev/sdb /mnt
linux-xtd6:~ # ls -l /mnt
total 0
-rw-r--r-- 1 root root 0 Oct 15 16:50 I am subvolume 2

I'm not sure when and how top level may become != 5.