[RFC pve-storage 06/27] diskmanage: link multipath member disks to their map device

[Dietmar Maurer <dietmar@proxmox.com>]

Multipath member disks only reported the generic 'Device Mapper'
usage, with no way to tell which map a member belongs to, or that
the device mapper holder is a multipath map at all. Report the
mapped device path in the new multipath property, so clients can
group paths by map or hide members in favor of the mapped device.

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>
---
 src/PVE/API2/Disks.pm                         |  6 ++++
 src/PVE/Diskmanage.pm                         | 33 +++++++++++++++++++
 .../multipath/disklist_expected.json          | 12 ++++---
 3 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/src/PVE/API2/Disks.pm b/src/PVE/API2/Disks.pm
index ee287f7..2417340 100644
--- a/src/PVE/API2/Disks.pm
+++ b/src/PVE/API2/Disks.pm
@@ -149,6 +149,12 @@ __PACKAGE__->register_method({
                         . 'example sata, sas, usb, fc, iscsi, nvme, nvme-fc, nvme-tcp).',
                     optional => 1,
                 },
+                multipath => {
+                    type => 'string',
+                    description => 'For multipath member devices only. The mapped '
+                        . 'device path of the multipath map the device belongs to.',
+                    optional => 1,
+                },
                 parent => {
                     type => 'string',
                     description => 'For partitions only. The device path of '
diff --git a/src/PVE/Diskmanage.pm b/src/PVE/Diskmanage.pm
index ed270e9..5ac04dd 100644
--- a/src/PVE/Diskmanage.pm
+++ b/src/PVE/Diskmanage.pm
@@ -535,12 +535,42 @@ sub mounted_paths {
     return $mounted;
 }
 
+# Maps multipath member devices (e.g. 'sda') to the mapped device path of
+# their multipath map (e.g. '/dev/mapper/mpatha').
+my sub get_multipath_slave_map {
+    my $slave_map = {};
+
+    dir_glob_foreach(
+        '/sys/block',
+        'dm-\d+',
+        sub {
+            my ($dev) = @_;
+            my $sysdir = "/sys/block/$dev";
+
+            my $uuid = file_read_firstline("$sysdir/dm/uuid") // return;
+            return if $uuid !~ m/^mpath-/;
+
+            my $name = file_read_firstline("$sysdir/dm/name") // return;
+
+            dir_glob_foreach(
+                "$sysdir/slaves",
+                '[^.].*',
+                sub { $slave_map->{ $_[0] } = "/dev/mapper/$name"; },
+            );
+        },
+    );
+
+    return $slave_map;
+}
+
 sub get_disks {
     my ($disks, $nosmart, $include_partitions) = @_;
     my $disklist = {};
 
     my $mounted = mounted_blockdevs();
 
+    my $mpath_slave_map = get_multipath_slave_map();
+
     my $lsblk_info = get_lsblk_info();
 
     my $journalhash = get_ceph_journals($lsblk_info);
@@ -655,6 +685,9 @@ sub get_disks {
             $disklist->{$dev}->{transport} = $transport if defined($transport);
             $disklist->{$dev}->{mounted} = 1 if exists $mounted->{$devpath};
 
+            my $mpath = $mpath_slave_map->{$dev};
+            $disklist->{$dev}->{multipath} = $mpath if defined($mpath);
+
             my $by_id_link = $data->{by_id_link};
             $disklist->{$dev}->{by_id_link} = $by_id_link if defined($by_id_link);
 
diff --git a/src/test/disk_tests/multipath/disklist_expected.json b/src/test/disk_tests/multipath/disklist_expected.json
index ec44296..001193d 100644
--- a/src/test/disk_tests/multipath/disklist_expected.json
+++ b/src/test/disk_tests/multipath/disklist_expected.json
@@ -15,7 +15,8 @@
         "osdid-list": null,
         "by_id_link": "/dev/disk/by-id/scsi-36001405000000000000000000000000a",
         "transport": "fc",
-        "used": "Device Mapper"
+        "used": "Device Mapper",
+        "multipath": "/dev/mapper/mpatha"
     },
     "sdb": {
         "devpath": "/dev/sdb",
@@ -33,7 +34,8 @@
         "osdid-list": null,
         "by_id_link": "/dev/disk/by-id/scsi-36001405000000000000000000000000b",
         "transport": "fc",
-        "used": "Device Mapper"
+        "used": "Device Mapper",
+        "multipath": "/dev/mapper/mpatha"
     },
     "sdc": {
         "devpath": "/dev/sdc",
@@ -51,7 +53,8 @@
         "osdid-list": null,
         "by_id_link": "/dev/disk/by-id/scsi-36001405000000000000000000000000c",
         "transport": "fc",
-        "used": "Device Mapper"
+        "used": "Device Mapper",
+        "multipath": "/dev/mapper/mpathb"
     },
     "sdd": {
         "devpath": "/dev/sdd",
@@ -69,7 +72,8 @@
         "osdid-list": null,
         "by_id_link": "/dev/disk/by-id/scsi-36001405000000000000000000000000d",
         "transport": "fc",
-        "used": "Device Mapper"
+        "used": "Device Mapper",
+        "multipath": "/dev/mapper/mpathb"
     },
     "nvme8n1": {
         "devpath": "/dev/nvme8n1",
-- 
2.47.3