> How can I test if a subvolume is a snapshot? [ ... ] This question is based on the assumption that "snapshot" is a distinct type of subvolume and not just an operation that creates a subvolume with reflinked contents. Unfortunately Btrfs does indeed make snapshots a distinct type of subvolume... In my 4.4 kernel/progs version of Btrfs it seems that the 'Parent UUID' is that of the source of the snapshot, and the source of a snapshot somehow comes with a list to all the snapshots taken from it: # ls /fs/sda7 = @170826 @170829 @170901 @170903 @170905 @170907 @170825 @170828 @170830 @170902 @170904 @170906 lost+found # btrfs subvolume list /fs/sda7 ID 431 gen 532441 top level 5 path = ID 1619 gen 524915 top level 5 path @170825 ID 1649 gen 524915 top level 5 path @170826 ID 1651 gen 524915 top level 5 path @170828 ID 1652 gen 524915 top level 5 path @170829 ID 1654 gen 524915 top level 5 path @170830 ID 1655 gen 523316 top level 5 path @170901 ID 1656 gen 524034 top level 5 path @170902 ID 1658 gen 525628 top level 5 path @170903 ID 1659 gen 527121 top level 5 path @170904 ID 1660 gen 528719 top level 5 path @170905 ID 1665 gen 530565 top level 5 path @170906 ID 1666 gen 532217 top level 5 path @170907 # btrfs subvolume show /fs/sda7/= | egrep 'UUID|Parent|Top level|Snap|@' UUID: cb99579f-64e5-e94c-b22c-41dcc397c37f Parent UUID: - Received UUID: - Parent ID: 5 Top level ID: 5 Snapshot(s): @170825 @170826 @170828 @170829 @170830 @170901 @170902 @170903 @170904 @170905 @170906 @170907 # btrfs subvolume show /fs/sda7/@170901 | egrep 'UUID|Parent|Top level|Snap|@' /fs/sda7/@170901 Name: @170901 UUID: 851f8ef3-c2af-4b46-89af-0193fd4e6fc4 Parent UUID: cb99579f-64e5-e94c-b22c-41dcc397c37f Received UUID: - Parent ID: 5 Top level ID: 5 Snapshot(s): Note that with typical Btrfs consistency "Parent UUID" is that the source of the snapshot, while "Parent ID" is that of the upper level subvolume, and in the "flat" layout for this volume the snapshot parent is '/fs/sda7/=' and the upper level is '/fs/sda7' instead. The different results that you get make me suspect that the top-level subvolume is "special". -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
