fix #5071: zfs over iscsi: add 'zfs-base-path' configuration option

Use '/dev/zvol' as a base path for new storages for providers 'iet'
and 'LIO', because that is what modern distributions use.

This is a breaking change regarding the addition of new storages on
older distributions, but it's enough to specify the base path '/dev'
explicitly for setups that require it.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Tested-by: Christoph Heiss <c.heiss@proxmox.com>
Link: https://lore.proxmox.com/20250605111109.52712-1-f.ebner@proxmox.com

src/PVE/Storage/LunCmd/Comstar.pm

@@ -32,7 +32,8 @@ my $get_lun_cmd_map = sub {
 };
 
 sub get_base {
-    return '/dev/zvol/rdsk';
+    my ($scfg) = @_;
+    return $scfg->{'zfs-base-path'} || '/dev/zvol/rdsk';
 }
 
 sub run_lun_command {

src/PVE/Storage/LunCmd/Iet.pm

@@ -138,7 +138,7 @@ my $parser = sub {
 
     my $line = 0;
 
-    my $base = get_base;
+    my $base = get_base($scfg);
     my $config = $get_config->($scfg);
     my @cfgfile = split "\n", $config;
 
@@ -482,7 +482,8 @@ sub run_lun_command {
 }
 
 sub get_base {
-    return '/dev';
+    my ($scfg) = @_;
+    return $scfg->{'zfs-base-path'} || '/dev';
 }
 
 1;

src/PVE/Storage/LunCmd/Istgt.pm

@@ -306,7 +306,7 @@ my $parser = sub {
     $CONFIG =~ s/\n$//;
     die "$scfg->{target}: Target not found" unless $SETTINGS->{targets};
     my $max = $SETTINGS->{targets};
-    my $base = get_base;
+    my $base = get_base($scfg);
 
     for (my $i = 1; $i <= $max; $i++) {
         my $target = $SETTINGS->{nodebase} . ':' . $SETTINGS->{"LogicalUnit$i"}->{TargetName};
@@ -612,7 +612,8 @@ sub run_lun_command {
 }
 
 sub get_base {
-    return '/dev/zvol';
+    my ($scfg) = @_;
+    return $scfg->{'zfs-base-path'} || '/dev/zvol';
 }
 
 1;

src/PVE/Storage/LunCmd/LIO.pm

@@ -231,7 +231,7 @@ my $extract_volname = sub {
     my ($scfg, $lunpath) = @_;
     my $volname = undef;
 
-    my $base = get_base;
+    my $base = get_base($scfg);
     if ($lunpath =~ /^$base\/$scfg->{pool}\/([\w\-]+)$/) {
         $volname = $1;
         my $prefix = $get_backstore_prefix->($scfg);
@@ -422,7 +422,8 @@ sub run_lun_command {
 }
 
 sub get_base {
-    return '/dev';
+    my ($scfg) = @_;
+    return $scfg->{'zfs-base-path'} || '/dev';
 }
 
 1;

src/PVE/Storage/ZFSPlugin.pm

@@ -38,13 +38,13 @@ my $zfs_get_base = sub {
     my ($scfg) = @_;
 
     if ($scfg->{iscsiprovider} eq 'comstar') {
-        return PVE::Storage::LunCmd::Comstar::get_base;
+        return PVE::Storage::LunCmd::Comstar::get_base($scfg);
     } elsif ($scfg->{iscsiprovider} eq 'istgt') {
-        return PVE::Storage::LunCmd::Istgt::get_base;
+        return PVE::Storage::LunCmd::Istgt::get_base($scfg);
     } elsif ($scfg->{iscsiprovider} eq 'iet') {
-        return PVE::Storage::LunCmd::Iet::get_base;
+        return PVE::Storage::LunCmd::Iet::get_base($scfg);
     } elsif ($scfg->{iscsiprovider} eq 'LIO') {
-        return PVE::Storage::LunCmd::LIO::get_base;
+        return PVE::Storage::LunCmd::LIO::get_base($scfg);
     } else {
         $zfs_unknown_scsi_provider->($scfg->{iscsiprovider});
     }
@@ -204,6 +204,12 @@ sub properties {
             description => "target portal group for Linux LIO targets",
             type => 'string',
         },
+        'zfs-base-path' => {
+            description => "Base path where to look for the created ZFS block devices. Set"
+                . " automatically during creation if not specified. Usually '/dev/zvol'.",
+            type => 'string',
+            format => 'pve-storage-path',
+        },
     };
 }
 
@@ -223,11 +229,36 @@ sub options {
         lio_tpg => { optional => 1 },
         content => { optional => 1 },
         bwlimit => { optional => 1 },
+        'zfs-base-path' => { optional => 1 },
     };
 }
 
 # Storage implementation
 
+sub on_add_hook {
+    my ($class, $storeid, $scfg, %param) = @_;
+
+    if (!$scfg->{'zfs-base-path'}) {
+        my $base_path;
+        if ($scfg->{iscsiprovider} eq 'comstar') {
+            $base_path = PVE::Storage::LunCmd::Comstar::get_base($scfg);
+        } elsif ($scfg->{iscsiprovider} eq 'istgt') {
+            $base_path = PVE::Storage::LunCmd::Istgt::get_base($scfg);
+        } elsif ($scfg->{iscsiprovider} eq 'iet' || $scfg->{iscsiprovider} eq 'LIO') {
+            # Provider implementations hard-code '/dev/', which does not work for distributions like
+            # Debian 12. Keep that implementation as-is for backwards compatibility, but use
+            # '/dev/zvol' here.
+            $base_path = '/dev/zvol';
+        } else {
+            $zfs_unknown_scsi_provider->($scfg->{iscsiprovider});
+        }
+
+        $scfg->{'zfs-base-path'} = $base_path;
+    }
+
+    return;
+}
+
 sub path {
     my ($class, $scfg, $volname, $storeid, $snapname) = @_;