[pve-devel] [PATCH storage] Fix #2050: only provide 'conv=sparse' for LvmThin

[Stoiko Ivanov]

LVMPlugin->volume_import (used during cross-node offline, storage migration)
passed 'conv=sparse' to `dd`. This can lead to data-corruption, if the target
volume is not zero-initialized.

Dropping the argument fixes the problem, but breaks keeping data sparse for
LvmThinPlugin.
This patch adds a sub to both Plugins for running the actual `dd` during
volume_import.

Signed-off-by: Stoiko Ivanov <s.ivanov at proxmox.com>
---
We had a short discussion off-list with Oguz and Wolfgang - putting the
complete dd command in a sub of its own enables us to potentially optimise it
in the future - e.g. to use the actual data_block_size as bs= parameter.
However for now I went with fixing the breakage and not optimizing the dd.

Steps for reproducing the issue:
* create a cluster with (at least) 2 nodes A and B, with a free disk-device (/dev/sdx)
* write a recognizable pattern to /dev/sdx on B:
  `dd if=/dev/zero bs=10M | tr '\000' '\255' | dd of=/dev/sdb bs=10M` #all 00 become ad
  (would be grateful for alternatives to the dd| tr| dd)
* on both A and B create a lvm-vg (pvcreate, vgcreate)
* add it as _not_ shared storage, which is available on nodes A and B
* create a small guest on A
* fill a file in the guest with zeros
  `dd if=/dev/zero of=/zerofil bs=10M`
* stop the guest, migrate it to B
* start the guest - check that the file `/zerofil` contains `ad` instead of `00`


 PVE/Storage/LVMPlugin.pm     | 10 ++++++++--
 PVE/Storage/LvmThinPlugin.pm |  7 +++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/PVE/Storage/LVMPlugin.pm b/PVE/Storage/LVMPlugin.pm
index 72d7464..9ad7979 100644
--- a/PVE/Storage/LVMPlugin.pm
+++ b/PVE/Storage/LVMPlugin.pm
@@ -620,8 +620,8 @@ sub volume_import {
 	}
 	my $file = $class->path($scfg, $volname, $storeid)
 	    or die "internal error: failed to get path to newly allocated volume $volname\n";
-	run_command(['dd', "of=$file", 'conv=sparse', 'bs=64k'],
-	            input => '<&'.fileno($fh));
+
+	$class->volume_import_write($fh, $file);
     };
     if (my $err = $@) {
 	eval { $class->free_image($storeid, $scfg, $volname, 0) };
@@ -630,4 +630,10 @@ sub volume_import {
     }
 }
 
+sub volume_import_write {
+    my ($class, $input_fh, $output_file) = @_;
+    run_command(['dd', "of=$output_file", 'bs=64k'],
+	input => '<&'.fileno($input_fh));
+}
+
 1;
diff --git a/PVE/Storage/LvmThinPlugin.pm b/PVE/Storage/LvmThinPlugin.pm
index 122fb37..aafc202 100644
--- a/PVE/Storage/LvmThinPlugin.pm
+++ b/PVE/Storage/LvmThinPlugin.pm
@@ -374,4 +374,11 @@ sub volume_has_feature {
     return undef;
 }
 
+# used in LVMPlugin->volume_import
+sub volume_import_write {
+    my ($class, $input_fh, $output_file) = @_;
+    run_command(['dd', "of=$output_file", 'conv=sparse', 'bs=64k'],
+	input => '<&'.fileno($input_fh));
+}
+
 1;
-- 
2.11.0