Re: [libvirt] [PATCHv2] logical: Add "--type snapshot" to lvcreate command

A recent lvm change has resulted in a change for the "default" type of logical volume created when the "--virtualsize" or "--V" is supplied on the command line (e.g. when the allocation and capacity values of a to be created volume differ). It seems that at the very least the following change adjusts the default type: https://git.fedorahosted.org/cgit/lvm2.git/commit/?id=e0164f21 and the following may also have some impact. https://git.fedorahosted.org/cgit/lvm2.git/commit/?id=87fc3b71 When using the virsh vol-create-as or vol-create xmlfile commands, the result is that libvirt will now create a "thin logical volume" and a "thin logical volume pool" rather than just a "thin snapshot logical volume". For example the following sequence: # lvcreate --name test -L 2M -V 5M lvm_test Rounding up size to full physical extent 4.00 MiB Rounding up size to full physical extent 8.00 MiB Logical volume "test" created. # lvs lvm_test LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert lvol1 lvm_test twi-a-tz-- 4.00m 0.00 0.98 test lvm_test Vwi-a-tz-- 8.00m lvol1 0.00 compared to the former code which had the following: LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert test LVM_Test swi-a-s--- 4.00m [test_vorigin] 0.00 Since libvirt doesn't know how to parse the thin logical volume and pool, it will fail to find the newly created volume and pool even though it exists in the volume group. It cannot find since the command used to find/parse returns a thin volume 'test' with no associated device, for example the output is: lvol1##UgUwkp-fTFP-C0rc-ufue-xrYh-dkPr-FGPFPx#lvol1_tdata(0)#thin-pool#1#4194304#4194304#4194304#twi-a-tz-- test##NcaIoH-4YWJ-QKu3-sJc3-EOcS-goff-cThLIL##thin#0#8388608#4194304#8388608#Vwi-a-tz-- as compared to the former which had the following: test#[test_vorigin]#Dt5Of3-4WE6-buvw-CWJ4-XOiz-ywOU-YULYw6#/dev/sda3(1300)#linear#1#4194304#4194304#4194304#swi-a-s--- While it's possible to generate code to handle the new thin lv and pool, this patch will add a "--type snapshot" onto the lvcreate command libvirt uses in order to "for now" be able to continue to utilize the thin snapshots Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; --- v1: http://www.redhat.com/archives/libvir-list/2014-December/msg00705.html The first version replaces thin snapshots with thin volumes and pools. Although it got an ACK, Jan Tomko points out rightfully so that perhaps we need more time to vet a change such as this - since it could be considered a few feature. So since using --type snapshot restores former functionality that should suffice until we can make sure we understand more about the differences between thin snapshots and thin volumes. src/storage/storage_backend_logical.c | 1 + 1 file changed, 1 insertion(+) diff --git a/src/storage/storage_backend_logical.c b/src/storage/storage_backend_logical.c index 4959985..8aa68a6 100644 --- a/src/storage/storage_backend_logical.c +++ b/src/storage/storage_backend_logical.c @@ -758,6 +758,7 @@ virStorageBackendLogicalCreateVol(virConnectPtr conn, virCommandAddArgFormat(cmd, "%lluK", VIR_DIV_UP(vol->target.allocation ? vol->target.allocation : 1, 1024)); + virCommandAddArgList(cmd, "--type", "snapshot", NULL); virCommandAddArg(cmd, "--virtualsize"); vol->target.sparse = true; }