This patch adds a section about seeding device for btrfs-man5. Description and examples are from btrfs-wiki page.
Signed-off-by: Sidong Yang <[email protected]> --- Documentation/btrfs-man5.asciidoc | 74 +++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) diff --git a/Documentation/btrfs-man5.asciidoc b/Documentation/btrfs-man5.asciidoc index e5edbe53..db2b5f1f 100644 --- a/Documentation/btrfs-man5.asciidoc +++ b/Documentation/btrfs-man5.asciidoc @@ -995,6 +995,80 @@ that report space usage: 'filesystem df', 'device usage'. The command --------------- +SEEDING DEVICE +-------------- + +The original filesystem and devices are included as a readonly starting point to +the new FS. All modifications go onto different devices and the COW machinery +makes sure the original is unchanged. + +-------------------- +# dd if=/dev/zero of=/mnt/gentoo/btrfs-test-1 count=2 bs=1G +# dd if=/dev/zero of=/mnt/gentoo/btrfs-test-2 count=2 bs=1G +-------------------- + +-------------------- +# losetup /dev/loop0 /mnt/gentoo/btrfs-test-1 +# losetup /dev/loop1 /mnt/gentoo/btrfs-test-2 +-------------------- + +-------------------- +# mkfs.btrfs /dev/loop0 +-------------------- + +-------------------- +# mount /dev/loop0 /mnt/test/ +# echo a > /mnt/test/a +# echo b > /mnt/test/b +-------------------- + +-------------------- +# umount /mnt/test +-------------------- + +Now we will use this filesystem as a seed device: +-------------------- +# btrfstune -S 1 /dev/loop0 +-------------------- +For more details, see `btrfstune`(8). + +-------------------- +# mount /dev/loop0 /mnt/test +mount: block device /dev/loop0 is write-protected, mounting read-only +# btrfs device add /dev/loop1 /mnt/test +# ls /mnt/test +a b +# echo c > /mnt/test/c +bash: c: Read-only file system +-------------------- + +-------------------- +# mount -o remount,rw /mnt/test +OR +# umount /mnt/test +# mount /dev/loop1 /mnt/test +-------------------- + +-------------------- +# echo c > /mnt/test/c +# echo d > /mnt/test/d +# umount /mnt/test +-------------------- + +-------------------- +# mount /dev/loop0 /mnt/test +mount: block device /dev/loop0 is write-protected, mounting read-only +# ls /mnt/test +a b +# umount /mnt/test +# mount /dev/loop1 /mnt/test +# ls /mnt/test +a b c d +# cat /mnt/test/c +c +-------------------- + + SEE ALSO -------- `acl`(5), -- 2.25.1
