[pve-devel] [RFC qemu-server v3 21/34] backup: implement backup for external providers

[Fiona Ebner <f.ebner@proxmox.com>]

The state of the VM's disk images at the time the backup is started is
preserved via a snapshot-access block node. Old data is moved to the
fleecing image when new guest writes come in. The snapshot-access
block node, as well as the associated bitmap in case of incremental
backup, will be made available to the external provider. They are
exported via NBD and for 'nbd' mechanism, the NBD socket path is
passed to the provider, while for 'block-device' mechanism, the NBD
export is made accessible as a regular block device first and the
bitmap information is made available via a $next_dirty_region->()
function. For 'block-device', the 'nbdinfo' binary is required.

The provider can indicate that it wants to do an incremental backup by
returning the bitmap ID that was used for a previous backup and it
will then be told if the bitmap was newly created (either first backup
or old bitmap was invalid) or if the bitmap can be reused.

The provider then reads the parts of the NBD or block device it needs,
either the full disk for full backup, or the dirty parts according to
the bitmap for incremental backup. The bitmap has to be respected,
reads to other parts of the image will return an error. After backing
up each part of the disk, it should be discarded in the export to
avoid unnecessary space usage in the fleecing image (requires the
storage underlying the fleecing image to support discard too).

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

Changes in v3:
* adapt to API changes, config files are now passed as raw

 PVE/VZDump/QemuServer.pm | 309 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 308 insertions(+), 1 deletion(-)

diff --git a/PVE/VZDump/QemuServer.pm b/PVE/VZDump/QemuServer.pm
index b6dcd6cc..d0218c9b 100644
--- a/PVE/VZDump/QemuServer.pm
+++ b/PVE/VZDump/QemuServer.pm
@@ -20,7 +20,7 @@ use PVE::QMPClient;
 use PVE::Storage::Plugin;
 use PVE::Storage::PBSPlugin;
 use PVE::Storage;
-use PVE::Tools;
+use PVE::Tools qw(run_command);
 use PVE::VZDump;
 use PVE::Format qw(render_duration render_bytes);
 
@@ -277,6 +277,8 @@ sub archive {
 
     if ($self->{vzdump}->{opts}->{pbs}) {
 	$self->archive_pbs($task, $vmid);
+    } elsif ($self->{vzdump}->{'backup-provider'}) {
+	$self->archive_external($task, $vmid);
     } else {
 	$self->archive_vma($task, $vmid, $filename, $comp);
     }
@@ -1149,6 +1151,23 @@ sub cleanup {
 
     # If VM was started only for backup, it is already stopped now.
     if (PVE::QemuServer::Helpers::vm_running_locally($vmid)) {
+	if ($task->{cleanup}->{'nbd-stop'}) {
+	    eval { PVE::QemuServer::QMPHelpers::nbd_stop($vmid); };
+	    $self->logerr($@) if $@;
+	}
+
+	if (my $info = $task->{cleanup}->{'backup-access-teardown'}) {
+	    my $params = {
+		'target-id' => $info->{'target-id'},
+		timeout => 60,
+		success => $info->{success} ? JSON::true : JSON::false,
+	    };
+
+	    $self->loginfo("tearing down backup-access");
+	    eval { mon_cmd($vmid, "backup-access-teardown", $params->%*) };
+	    $self->logerr($@) if $@;
+	}
+
 	$detach_tpmstate_drive->($task, $vmid);
 	detach_fleecing_images($task->{disks}, $vmid) if $task->{'use-fleecing'};
     }
@@ -1160,4 +1179,292 @@ sub cleanup {
     }
 }
 
+my sub block_device_backup_cleanup {
+    my ($self, $paths, $cpids) = @_;
+
+    for my $path ($paths->@*) {
+	eval { run_command(["qemu-nbd", "-d", $path ]); };
+	$self->log('warn', "unable to disconnect NBD backup source '$path' - $@") if $@;
+    }
+
+    my $waited;
+    my $wait_limit = 5;
+    for ($waited = 0; $waited < $wait_limit && scalar(keys $cpids->%*); $waited++) {
+	while ((my $cpid = waitpid(-1, POSIX::WNOHANG)) > 0) {
+	    delete($cpids->{$cpid});
+	}
+	if ($waited == 0) {
+	    kill 15, $_ for keys $cpids->%*;
+	}
+	sleep 1;
+    }
+    if ($waited == $wait_limit && scalar(keys $cpids->%*)) {
+	kill 9, $_ for keys $cpids->%*;
+	sleep 1;
+	while ((my $cpid = waitpid(-1, POSIX::WNOHANG)) > 0) {
+	    delete($cpids->{$cpid});
+	}
+	$self->log('warn', "unable to collect nbdinfo child process '$_'") for keys $cpids->%*;
+    }
+}
+
+my sub block_device_backup_prepare {
+    my ($self, $devicename, $size, $nbd_path, $bitmap_name, $count) = @_;
+
+    my $nbd_info_uri = "nbd+unix:///${devicename}?socket=${nbd_path}";
+    my $qemu_nbd_uri = "nbd:unix:${nbd_path}:exportname=${devicename}";
+
+    my $cpid;
+    my $error_fh;
+    my $next_dirty_region;
+
+    # If there is no dirty bitmap, it can be treated as if there's a full dirty one. The output of
+    # nbdinfo is a list of tuples with offset, length, type, description. The first bit of 'type' is
+    # set when the bitmap is dirty, see QEMU's docs/interop/nbd.txt
+    my $dirty_bitmap = [];
+    if ($bitmap_name) {
+	my $input = IO::File->new();
+	my $info = IO::File->new();
+	$error_fh = IO::File->new();
+	my $nbdinfo_cmd = ["nbdinfo", $nbd_info_uri, "--map=qemu:dirty-bitmap:${bitmap_name}"];
+	$cpid = open3($input, $info, $error_fh, $nbdinfo_cmd->@*)
+	    or die "failed to spawn nbdinfo child - $!\n";
+
+	$next_dirty_region = sub {
+	    my ($offset, $length, $type);
+	    do {
+		my $line = <$info>;
+		return if !$line;
+		die "unexpected output from nbdinfo - $line\n"
+		    if $line !~ m/^\s*(\d+)\s*(\d+)\s*(\d+)/; # also untaints
+		($offset, $length, $type) = ($1, $2, $3);
+	    } while (($type & 0x1) == 0); # not dirty
+	    return ($offset, $length);
+	};
+    } else {
+	my $done = 0;
+	$next_dirty_region = sub {
+	    return if $done;
+	    $done = 1;
+	    return (0, $size);
+	};
+    }
+
+    my $blockdev = "/dev/nbd${count}";
+
+    eval {
+	run_command(["qemu-nbd", "-c", $blockdev, $qemu_nbd_uri, "--format=raw", "--discard=on"]);
+    };
+    if (my $err = $@) {
+	my $cpids = {};
+	$cpids->{$cpid} = 1 if $cpid;
+	block_device_backup_cleanup($self, [$blockdev], $cpids);
+	die $err;
+    }
+
+    return ($blockdev, $next_dirty_region, $cpid);
+}
+
+my sub backup_access_to_volume_info {
+    my ($self, $backup_access_info, $mechanism, $nbd_path) = @_;
+
+    my $child_pids = {}; # used for nbdinfo calls
+    my $count = 0; # counter for block devices, i.e. /dev/nbd${count}
+    my $volumes = {};
+
+    for my $info ($backup_access_info->@*) {
+	my $bitmap_status = 'none';
+	my $bitmap_name;
+	if (my $bitmap_action = $info->{'bitmap-action'}) {
+	    my $bitmap_action_to_status = {
+		'not-used' => 'none',
+		'not-used-removed' => 'none',
+		'new' => 'new',
+		'used' => 'reuse',
+		'invalid' => 'new',
+	    };
+
+	    $bitmap_status = $bitmap_action_to_status->{$bitmap_action}
+		or die "got unexpected bitmap action '$bitmap_action'\n";
+
+	    $bitmap_name = $info->{'bitmap-name'} or die "bitmap-name is not present\n";
+	}
+
+	my ($device, $size) = $info->@{qw(device size)};
+
+	$volumes->{$device}->{'bitmap-mode'} = $bitmap_status;
+	$volumes->{$device}->{size} = $size;
+
+	if ($mechanism eq 'block-device') {
+	    my ($blockdev, $next_dirty_region, $child_pid) = block_device_backup_prepare(
+		$self, $device, $size, $nbd_path, $bitmap_name, $count);
+	    $count++;
+	    $child_pids->{$child_pid} = 1 if $child_pid;
+	    $volumes->{$device}->{path} = $blockdev;
+	    $volumes->{$device}->{'next-dirty-region'} = $next_dirty_region;
+	} elsif ($mechanism eq 'nbd') {
+	    $volumes->{$device}->{'nbd-path'} = $nbd_path;
+	    $volumes->{$device}->{'bitmap-name'} = $bitmap_name;
+	} else {
+	    die "internal error - unkown mechanism '$mechanism'";
+	}
+    }
+
+    return ($volumes, $child_pids);
+}
+
+sub archive_external {
+    my ($self, $task, $vmid) = @_;
+
+    my $guest_config = PVE::Tools::file_get_contents("$task->{tmpdir}/qemu-server.conf");
+    my $firewall_file = "$task->{tmpdir}/qemu-server.fw";
+
+    my $opts = $self->{vzdump}->{opts};
+
+    my $backup_provider = $self->{vzdump}->{'backup-provider'};
+
+    $self->loginfo("starting external backup via " . $backup_provider->provider_name());
+
+    my $starttime = time();
+
+    # get list early so we die on unkown drive types before doing anything
+    my $devlist = _get_task_devlist($task);
+
+    $self->enforce_vm_running_for_backup($vmid);
+    $self->{qmeventd_fh} = PVE::QemuServer::register_qmeventd_handle($vmid);
+
+    eval {
+	$SIG{INT} = $SIG{TERM} = $SIG{QUIT} = $SIG{HUP} = $SIG{PIPE} = sub {
+	    die "interrupted by signal\n";
+	};
+
+	my $qemu_support = mon_cmd($vmid, "query-proxmox-support");
+
+	$attach_tpmstate_drive->($self, $task, $vmid);
+
+	my $is_template = PVE::QemuConfig->is_template($self->{vmlist}->{$vmid});
+
+	my $fleecing = check_and_prepare_fleecing(
+	    $self, $task, $vmid, $opts->{fleecing}, $task->{disks}, $is_template, $qemu_support, 1);
+	die "cannot setup backup access without fleecing\n" if !$fleecing;
+
+	$task->{'use-fleecing'} = 1;
+
+	my $fs_frozen = $self->qga_fs_freeze($task, $vmid);
+
+	my $target_id = $opts->{storage};
+
+	my $params = {
+	    'target-id' => $target_id,
+	    devlist => $devlist,
+	    timeout => 60,
+	};
+
+	my ($mechanism, $bitmap_name) = $backup_provider->backup_get_mechanism($vmid, 'qemu');
+	die "mechanism '$mechanism' requested by backup provider is not supported for VMs\n"
+	    if $mechanism ne 'block-device' && $mechanism ne 'nbd';
+
+	if ($mechanism eq 'block-device') {
+	    # For mechanism 'block-device' the bitmap needs to be passed to the provider. The bitmap
+	    # cannot be dumped via QMP and doing it via qemu-img is experimental, so use nbdinfo.
+	    die "need 'nbdinfo' binary from package libnbd-bin\n" if !-e "/usr/bin/nbdinfo";
+
+	    # NOTE nbds_max won't change if module is already loaded
+	    run_command(["modprobe", "nbd", "nbds_max=128"]);
+	}
+
+	if ($bitmap_name) {
+	    # prepend storage ID so different providers can never cause clashes
+	    $bitmap_name = "$opts->{storage}-" . $bitmap_name;
+	    $params->{'bitmap-name'} = $bitmap_name;
+	}
+
+	$self->loginfo("setting up snapshot-access for backup");
+
+	my $backup_access_info = eval { mon_cmd($vmid, "backup-access-setup", $params->%*) };
+	my $qmperr = $@;
+
+	$task->{cleanup}->{'backup-access-teardown'} = { 'target-id' => $target_id, success => 0 };
+
+	if ($fs_frozen) {
+	    $self->qga_fs_thaw($vmid);
+	}
+
+	die $qmperr if $qmperr;
+
+	$self->resume_vm_after_job_start($task, $vmid);
+
+	my $bitmap_info = mon_cmd($vmid, 'query-pbs-bitmap-info');
+	for my $info (sort { $a->{drive} cmp $b->{drive} } $bitmap_info->@*) {
+	    my $text = $bitmap_action_to_human->($self, $info);
+	    my $drive = $info->{drive};
+	    $drive =~ s/^drive-//; # for consistency
+	    $self->loginfo("$drive: dirty-bitmap status: $text");
+	}
+
+	$self->loginfo("starting NBD server");
+
+	my $nbd_path = "/run/qemu-server/$vmid\_nbd.backup_access";
+	mon_cmd(
+	    $vmid, "nbd-server-start", addr => { type => 'unix', data => { path => $nbd_path } } );
+	$task->{cleanup}->{'nbd-stop'} = 1;
+
+	for my $info ($backup_access_info->@*) {
+	    $self->loginfo("adding NBD export for $info->{device}");
+
+	    my $export_params = {
+		id => $info->{device},
+		'node-name' => $info->{'node-name'},
+		writable => JSON::true, # for discard
+		type => "nbd",
+		name => $info->{device}, # NBD export name
+	    };
+
+	    if ($info->{'bitmap-name'}) {
+		$export_params->{bitmaps} = [{
+		    node => $info->{'bitmap-node-name'},
+		    name => $info->{'bitmap-name'},
+		}],
+	    }
+
+	    mon_cmd($vmid, "block-export-add", $export_params->%*);
+	}
+
+	my $child_pids = {}; # used for nbdinfo calls
+	my $volumes = {};
+
+	eval {
+	    ($volumes, $child_pids) =
+		backup_access_to_volume_info($self, $backup_access_info, $mechanism, $nbd_path);
+
+	    my $param = {};
+	    $param->{'bandwidth-limit'} = $opts->{bwlimit} * 1024 if $opts->{bwlimit};
+	    $param->{'firewall-config'} = PVE::Tools::file_get_contents($firewall_file)
+		if -e $firewall_file;
+
+	    $backup_provider->backup_vm($vmid, $guest_config, $volumes, $param);
+	};
+	my $err = $@;
+
+	if ($mechanism eq 'block-device') {
+	    my $cleanup_paths = [map { $volumes->{$_}->{path} } keys $volumes->%*];
+	    block_device_backup_cleanup($self, $cleanup_paths, $child_pids)
+	}
+
+	die $err if $err;
+    };
+    my $err = $@;
+
+    if ($err) {
+	$self->logerr($err);
+	$self->resume_vm_after_job_start($task, $vmid);
+    } else {
+	$task->{size} = $backup_provider->backup_get_task_size($vmid);
+	$task->{cleanup}->{'backup-access-teardown'}->{success} = 1;
+    }
+    $self->restore_vm_power_state($vmid);
+
+    die $err if $err;
+}
+
 1;
-- 
2.39.5



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