fix #3580: plugins: make preallocation mode selectable for qcow2 and raw images

the plugins for file based storages
 * BTRFS
 * CIFS
 * Dir
 * Glusterfs
 * NFS
now allow the option 'preallocation'.

'preallocation' can have four values:
 * default
 * off
 * metadata
 * falloc
 * full
see man pages for `qemu-img` for what these mean exactly. [0]

the defualt value was chosen to be
 * qcow2: metadata (as previously)
 * raw: off

when using 'metadata' as preallocation mode, for raw images 'off'
is used.

[0] https://qemu.readthedocs.io/en/latest/system/images.html#disk-image-file-formats

Signed-off-by: Lorenz Stechauner <l.stechauner@proxmox.com>
Reviewed-by: Fabian Ebner <f.ebner@proxmox.com>
Tested-by: Fabian Ebner <f.ebner@proxmox.com>

PVE/Storage/BTRFSPlugin.pm

@@ -73,6 +73,7 @@ sub options {
 	is_mountpoint => { optional => 1 },
 	nocow => { optional => 1 },
 	mkdir => { optional => 1 },
+	preallocation => { optional => 1 },
 	# TODO: The new variant of mkdir with  `populate` vs `create`...
     };
 }

PVE/Storage/CIFSPlugin.pm

@@ -142,6 +142,7 @@ sub options {
 	smbversion => { optional => 1},
 	mkdir => { optional => 1 },
 	bwlimit => { optional => 1 },
+	preallocation => { optional => 1 },
     };
 }
 

PVE/Storage/DirPlugin.pm

@@ -59,6 +59,7 @@ sub options {
 	mkdir => { optional => 1 },
 	is_mountpoint => { optional => 1 },
 	bwlimit => { optional => 1 },
+	preallocation => { optional => 1 },
    };
 }
 

PVE/Storage/GlusterfsPlugin.pm

@@ -137,6 +137,7 @@ sub options {
 	format => { optional => 1 },
 	mkdir => { optional => 1 },
 	bwlimit => { optional => 1 },
+	preallocation => { optional => 1 },
     };
 }
 
@@ -260,7 +261,8 @@ sub alloc_image {
 
     my $cmd = ['/usr/bin/qemu-img', 'create'];
 
-    push @$cmd, '-o', 'preallocation=metadata' if $fmt eq 'qcow2';
+    my $prealloc_opt = PVE::Storage::Plugin::preallocation_cmd_option($scfg, $fmt);
+    push @$cmd, '-o', $prealloc_opt if defined($prealloc_opt);
 
     push @$cmd, '-f', $fmt, $volumepath, "${size}K";
 

PVE/Storage/NFSPlugin.pm

@@ -90,6 +90,7 @@ sub options {
 	format => { optional => 1 },
 	mkdir => { optional => 1 },
 	bwlimit => { optional => 1 },
+	preallocation => { optional => 1 },
     };
 }
 

PVE/Storage/Plugin.pm

@@ -41,6 +41,19 @@ our @SHARED_STORAGE = (
     'pbs',
 );
 
+our $QCOW2_PREALLOCATION = {
+    off => 1,
+    metadata => 1,
+    falloc => 1,
+    full => 1,
+};
+
+our $RAW_PREALLOCATION = {
+    off => 1,
+    falloc => 1,
+    full => 1,
+};
+
 our $MAX_VOLUMES_PER_GUEST = 1024;
 
 cfs_register_file ('storage.cfg',
@@ -152,6 +165,13 @@ my $defaultData = {
 	    type => 'string', format => 'pve-storage-format',
 	    optional => 1,
 	},
+	preallocation => {
+	    description => "Preallocation mode for raw and qcow2 images. " .
+		"Using 'metadata' on raw images results in preallocation=off.",
+	    type => 'string', enum => ['off', 'metadata', 'falloc', 'full'],
+	    default => 'metadata',
+	    optional => 1,
+	},
     },
 };
 
@@ -444,6 +464,31 @@ sub parse_config {
     return $cfg;
 }
 
+sub preallocation_cmd_option {
+    my ($scfg, $fmt) = @_;
+
+    my $prealloc = $scfg->{preallocation};
+
+    if ($fmt eq 'qcow2') {
+	$prealloc = $prealloc // 'metadata';
+
+	die "preallocation mode '$prealloc' not supported by format '$fmt'\n"
+	    if !$QCOW2_PREALLOCATION->{$prealloc};
+
+	return "preallocation=$prealloc";
+    } elsif ($fmt eq 'raw') {
+	$prealloc = $prealloc // 'off';
+	$prealloc = 'off' if $prealloc eq 'metadata';
+
+	die "preallocation mode '$prealloc' not supported by format '$fmt'\n"
+	    if !$RAW_PREALLOCATION->{$prealloc};
+
+	return "preallocation=$prealloc";
+    }
+
+    return;
+}
+
 # Storage implementation
 
 # called during addition of storage (before the new storage config got written)
@@ -764,7 +809,8 @@ sub alloc_image {
     } else {
 	my $cmd = ['/usr/bin/qemu-img', 'create'];
 
-	push @$cmd, '-o', 'preallocation=metadata' if $fmt eq 'qcow2';
+	my $prealloc_opt = preallocation_cmd_option($scfg, $fmt);
+	push @$cmd, '-o', $prealloc_opt if defined($prealloc_opt);
 
 	push @$cmd, '-f', $fmt, $path, "${size}K";