[pve-devel] [PATCH qemu-server v2 3/5] fix #6675: template backup: fix regression with IDE/SATA and blockdev

[Fiona Ebner]

With ide-hd, the inserted block node needs to be marked as writable
too, but -blockdev will complain if it's marked as writable but the
actual backing device is read-only (e.g. read-only base LV).

IDE/SATA do not support being configured as read-only, the most
similar is using ide-cd instead of ide-hd, with most of the code and
configuration shared in QEMU.

Since a template is never actually started, the front-end device is
never accessed. The backup only accesses the inserted block node, so
it does not matter for the backup if the type is 'ide-cd' instead.

The same issue did not manifest for '-drive', because the '-snapshot'
option is used for template backups. The '-snapshot' option does not
affect '-blockdev', from 'man kvm':

> snapshot is incompatible with -blockdev

Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---
 src/PVE/QemuServer.pm                      | 13 ++++++++++---
 src/test/cfg2cmd/simple1-template.conf.cmd |  4 ++--
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index 67db9bc3..d3f0c589 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -1272,6 +1272,15 @@ sub print_drivedevice_full {
 
         my $device_type = ($drive->{media} && $drive->{media} eq 'cdrom') ? "cd" : "hd";
 
+        # With ide-hd, the inserted block node needs to be marked as writable too, but -blockdev
+        # will complain if it's marked as writable but the actual backing device is read-only (e.g.
+        # read-only base LV). IDE/SATA do not support being configured as read-only, the most
+        # similar is using ide-cd instead of ide-hd, with most of the code and configuration shared
+        # in QEMU. Since a template is never actually started, the front-end device is never
+        # accessed. The backup only accesses the inserted block node, so it does not matter for the
+        # backup if the type is 'ide-cd' instead.
+        $device_type = 'cd' if $conf->{template};
+
         $device = "ide-$device_type";
         if ($drive->{interface} eq 'ide') {
             $device .= ",bus=ide.$controller,unit=$unit";
@@ -3752,9 +3761,7 @@ sub config_to_command {
 
                     my $extra_blockdev_options = {};
                     $extra_blockdev_options->{'live-restore'} = $live_restore if $live_restore;
-                    # extra protection for templates, but SATA and IDE don't support it..
-                    $extra_blockdev_options->{'read-only'} = 1
-                        if drive_is_read_only($conf, $drive);
+                    $extra_blockdev_options->{'read-only'} = 1 if $is_template;
 
                     my $blockdev = PVE::QemuServer::Blockdev::generate_drive_blockdev(
                         $storecfg, $drive, $machine_version, $extra_blockdev_options,
diff --git a/src/test/cfg2cmd/simple1-template.conf.cmd b/src/test/cfg2cmd/simple1-template.conf.cmd
index df51a4a5..369b4de9 100644
--- a/src/test/cfg2cmd/simple1-template.conf.cmd
+++ b/src/test/cfg2cmd/simple1-template.conf.cmd
@@ -30,7 +30,7 @@
   -blockdev '{"detect-zeroes":"unmap","discard":"unmap","driver":"throttle","file":{"cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"file","filename":"/var/lib/vz/images/8006/base-8006-disk-1.qcow2","node-name":"e1085774206ae4a6b6bf8426ff08f16","read-only":true},"node-name":"f1085774206ae4a6b6bf8426ff08f16","read-only":true},"node-name":"drive-scsi0","read-only":true,"throttle-group":"throttle-drive-scsi0"}' \
   -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,device_id=drive-scsi0,write-cache=on' \
   -device 'ahci,id=ahci0,multifunction=on,bus=pci.0,addr=0x7' \
-  -blockdev '{"detect-zeroes":"unmap","discard":"unmap","driver":"throttle","file":{"cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"file","filename":"/var/lib/vz/images/8006/base-8006-disk-0.qcow2","node-name":"eab334c2e07734480f33dd80d89871b","read-only":false},"node-name":"fab334c2e07734480f33dd80d89871b","read-only":false},"node-name":"drive-sata0","read-only":false,"throttle-group":"throttle-drive-sata0"}' \
-  -device 'ide-hd,bus=ahci0.0,drive=drive-sata0,id=sata0,write-cache=on' \
+  -blockdev '{"detect-zeroes":"unmap","discard":"unmap","driver":"throttle","file":{"cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"unmap","discard":"unmap","driver":"file","filename":"/var/lib/vz/images/8006/base-8006-disk-0.qcow2","node-name":"eab334c2e07734480f33dd80d89871b","read-only":true},"node-name":"fab334c2e07734480f33dd80d89871b","read-only":true},"node-name":"drive-sata0","read-only":true,"throttle-group":"throttle-drive-sata0"}' \
+  -device 'ide-cd,bus=ahci0.0,drive=drive-sata0,id=sata0,write-cache=on' \
   -machine 'accel=tcg,smm=off,type=pc+pve0' \
   -snapshot
-- 
2.47.2