[pve-devel] [PATCH qemu-server 20/22] blockdev: add helpers to generate blockdev commandline
Fiona Ebner
f.ebner at proxmox.com
Thu Jun 12 16:02:51 CEST 2025
The drive device and node structure is:
front-end device {ide-hd,scsi-hd,virtio-blk-pci} (id=$drive_id)
- throttle node (node-name=$drive_id)
- format node (node-name=f$encoded-info)
- file node (node-name=e$encoded-info)
The node-name can only be 31 characters long and needs to start with a
letter. The throttle node will stay inserted below the front-end
device. The other nodes might change however, because of drive
mirroring and similar. There currently are no good helpers to
query/walk the block graph via QMP, x-debug-query-block-graph is
experimental and for debugging only. Therefore, necessary information
is encoded in the node name to be able to find it again. In
particular, this is the volume ID, the drive ID and optionally a
snapshot name. As long as the configuration file matches with the
running instance, this is enough to find the correct node for
block operations like mirror and resize.
The 'snapshot' option, for QEMU's snapshot mode, i.e. writes are only
temporary, is not yet supported.
Originally-by: Alexandre Derumier <alexandre.derumier at groupe-cyllene.com>
[FE: split up patch
expand commit message
explicitly test for drivers with aio setting
improve readonly handling
improve CD-ROM handling
fix failure for storage named 'nbd' by always using full regex
improve node name generation
fail when drive->{snapshot} is set]
Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---
If we do not get around to implement the 'snapshot' option in time for
PVE 9, we can still fall back to the legacy drive for that (and warn
users that not all operations might work with such drives).
PVE/QemuServer/Blockdev.pm | 172 ++++++++++++++++++++++++++++++++++++-
PVE/QemuServer/Makefile | 1 +
2 files changed, 172 insertions(+), 1 deletion(-)
diff --git a/PVE/QemuServer/Blockdev.pm b/PVE/QemuServer/Blockdev.pm
index b1150141..2d3760f0 100644
--- a/PVE/QemuServer/Blockdev.pm
+++ b/PVE/QemuServer/Blockdev.pm
@@ -3,7 +3,42 @@ package PVE::QemuServer::Blockdev;
use strict;
use warnings;
-use PVE::QemuServer::Drive;
+use Digest::SHA;
+use Fcntl qw(S_ISBLK S_ISCHR);
+use File::stat;
+use JSON;
+
+use PVE::Storage;
+
+use PVE::QemuServer::Drive qw(drive_is_cdrom);
+
+my sub get_node_name {
+ my ($type, $drive_id, $volid, $snap) = @_;
+
+ my $info = "drive=$drive_id,";
+ $info .= "snap=$snap," if defined($snap);
+ $info .= "volid=$volid";
+
+ my $hash = substr(Digest::SHA::sha256_hex($info), 0, 30);
+
+ my $prefix = "";
+ if ($type eq 'fmt') {
+ $prefix = 'f';
+ } elsif ($type eq 'file') {
+ $prefix = 'e';
+ } else {
+ die "unknown node type '$type'";
+ }
+ # node-name must start with an alphabetical character
+ return "${prefix}${hash}";
+}
+
+my sub read_only_json_option {
+ my ($drive, $options) = @_;
+
+ return JSON::true if $drive->{ro} || drive_is_cdrom($drive) || $options->{'read-only'};
+ return JSON::false;
+}
sub generate_throttle_group {
my ($drive) = @_;
@@ -41,4 +76,139 @@ sub generate_throttle_group {
};
}
+sub generate_blockdev_drive_cache {
+ my ($drive, $scfg) = @_;
+
+ my $cache_direct = PVE::QemuServer::Drive::drive_uses_cache_direct($drive, $scfg);
+ my $cache = {};
+ $cache->{direct} = $cache_direct ? JSON::true : JSON::false;
+ $cache->{'no-flush'} = $drive->{cache} && $drive->{cache} eq 'unsafe' ? JSON::true : JSON::false;
+ return $cache;
+}
+
+sub generate_file_blockdev {
+ my ($storecfg, $drive, $options) = @_;
+
+ my $blockdev = {};
+ my $scfg = undef;
+
+ die "generate_file_blockdev called without volid/path\n" if !$drive->{file};
+ die "generate_file_blockdev called with 'none'\n" if $drive->{file} eq 'none';
+ # FIXME use overlay and new config option to define storage for temp write device
+ die "'snapshot' option is not yet supported for '-blockdev'\n" if $drive->{snapshot};
+
+ my $drive_id = PVE::QemuServer::Drive::get_drive_id($drive);
+
+ if ($drive->{file} eq 'cdrom') {
+ my $path = PVE::QemuServer::Drive::get_iso_path($storecfg, $drive->{file});
+ $blockdev = { driver => 'host_cdrom', filename => $path };
+ } elsif ($drive->{file} =~ m|^/|) {
+ my $path = $drive->{file};
+ # The 'file' driver only works for regular files. The check below is taken from
+ # block/file-posix.c:hdev_probe_device() in QEMU. To detect CD-ROM host devices, QEMU issues
+ # an ioctl, while the code here relies on the media=cdrom flag instead.
+ my $st = File::stat::stat($path) or die "stat for '$path' failed - $!\n";
+ my $driver = 'file';
+ if (S_ISCHR($st->mode) || S_ISBLK($st->mode)) {
+ $driver = drive_is_cdrom($drive) ? 'host_cdrom' : 'host_device';
+ }
+ $blockdev = { driver => $driver, filename => $path };
+ } else {
+ my $volid = $drive->{file};
+ my ($storeid) = PVE::Storage::parse_volume_id($volid);
+
+ my $vtype = (PVE::Storage::parse_volname($storecfg, $drive->{file}))[0];
+ die "$drive_id: explicit media parameter is required for iso images\n"
+ if !defined($drive->{media}) && defined($vtype) && $vtype eq 'iso';
+
+ my $storage_opts = { hints => {} };
+ $storage_opts->{hints}->{'efi-disk'} = 1 if $drive->{interface} eq 'efidisk';
+ $storage_opts->{'snapshot-name'} = $options->{'snapshot-name'}
+ if defined($options->{'snapshot-name'});
+ $blockdev = PVE::Storage::qemu_blockdev_options($storecfg, $volid, $storage_opts);
+ $scfg = PVE::Storage::storage_config($storecfg, $storeid);
+ }
+
+ $blockdev->{cache} = generate_blockdev_drive_cache($drive, $scfg);
+
+ my $driver = $blockdev->{driver};
+ # only certain drivers have the aio setting
+ if ($driver eq 'file' || $driver eq 'host_cdrom' || $driver eq 'host_device') {
+ $blockdev->{aio} = PVE::QemuServer::Drive::aio_cmdline_option(
+ $scfg, $drive, $blockdev->{cache}->{direct});
+ }
+
+ if (!drive_is_cdrom($drive)) {
+ $blockdev->{discard} = $drive->{discard} && $drive->{discard} eq 'on' ? 'unmap' : 'ignore';
+ $blockdev->{'detect-zeroes'} = PVE::QemuServer::Drive::detect_zeroes_cmdline_option($drive);
+ }
+
+ $blockdev->{'node-name'} = get_node_name(
+ 'file', $drive_id, $drive->{file}, $options->{'snapshot-name'});
+
+ $blockdev->{'read-only'} = read_only_json_option($drive, $options);
+
+ return $blockdev;
+}
+
+sub generate_format_blockdev {
+ my ($storecfg, $drive, $child, $options) = @_;
+
+ die "generate_format_blockdev called without volid/path\n" if !$drive->{file};
+ die "generate_format_blockdev called with 'none'\n" if $drive->{file} eq 'none';
+
+ my $scfg;
+ my $format;
+ my $volid = $drive->{file};
+ my $drive_id = PVE::QemuServer::Drive::get_drive_id($drive);
+ my ($storeid) = PVE::Storage::parse_volume_id($volid, 1);
+
+ # For PVE-managed volumes, use the format from the storage layer and prevent overrides via the
+ # drive's 'format' option. For unmanaged volumes, fallback to 'raw' to avoid auto-detection by
+ # QEMU.
+ if ($storeid) {
+ $scfg = PVE::Storage::storage_config($storecfg, $storeid);
+ $format = PVE::QemuServer::Drive::checked_volume_format($storecfg, $volid);
+ if ($drive->{format} && $drive->{format} ne $format) {
+ die "drive '$drive->{interface}$drive->{index}' - volume '$volid'"
+ ." - 'format=$drive->{format}' option different from storage format '$format'\n";
+ }
+ } else {
+ $format = $drive->{format} // 'raw';
+ }
+
+ # define cache option on both format && file node like libvirt does
+ my $cache = generate_blockdev_drive_cache($drive, $scfg);
+
+ my $node_name = get_node_name('fmt', $drive_id, $drive->{file}, $options->{'snapshot-name'});
+
+ return {
+ 'node-name' => "$node_name",
+ driver => "$format",
+ file => $child,
+ cache => $cache,
+ 'read-only' => read_only_json_option($drive, $options),
+ };
+}
+
+sub generate_drive_blockdev {
+ my ($storecfg, $drive, $options) = @_;
+
+ my $drive_id = PVE::QemuServer::Drive::get_drive_id($drive);
+
+ die "generate_drive_blockdev called without volid/path\n" if !$drive->{file};
+ die "generate_drive_blockdev called with 'none'\n" if $drive->{file} eq 'none';
+
+ my $child = generate_file_blockdev($storecfg, $drive, $options);
+ $child = generate_format_blockdev($storecfg, $drive, $child, $options);
+
+ # this is the top filter entry point, use $drive-drive_id as nodename
+ return {
+ driver => "throttle",
+ 'node-name' => "drive-$drive_id",
+ 'throttle-group' => "throttle-drive-$drive_id",
+ file => $child,
+ };
+}
+
1;
diff --git a/PVE/QemuServer/Makefile b/PVE/QemuServer/Makefile
index 8054a93b..e3671e5b 100644
--- a/PVE/QemuServer/Makefile
+++ b/PVE/QemuServer/Makefile
@@ -12,6 +12,7 @@ SOURCES=PCI.pm \
MetaInfo.pm \
CPUConfig.pm \
CGroup.pm \
+ Blockdev.pm \
Drive.pm \
QMPHelpers.pm \
StateFile.pm \
--
2.39.5
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