[pve-devel] [PATCH qemu-server v2 1/1] add ivshmem device to config

[Dominik Csapak]

with such a shared memory device, a vm can share data with other
vms or with the host via memory

one of the use cases is looking-glass[1] with pci-passthrough, which copies
the guest fb to the host and you get a high-speed, low-latency
display client for the vm

on vm stop we delete the file again

1: https://looking-glass.hostfission.com/

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
 PVE/QemuServer.pm     | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 PVE/QemuServer/PCI.pm |  2 ++
 2 files changed, 48 insertions(+)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 6dc68a4..95d22ca 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -256,6 +256,21 @@ my $vga_fmt = {
     },
 };
 
+my $ivshmem_fmt = {
+    size => {
+	type => 'integer',
+	minimum => 1,
+	description => "The size of the file in MB.",
+    },
+    name => {
+	type => 'string',
+	pattern => '[a-zA-Z0-9\-]+',
+	optional => 1,
+	format_description => 'string',
+	description => "The name of the file. Will be prefixed with 'pve-shm-'. Default is the VMID. Will be deleted when the VM is stopped.",
+    },
+};
+
 my $confdesc = {
     onboot => {
 	optional => 1,
@@ -621,6 +636,12 @@ EODESCR
 	optional => 1,
 	description => "Script that will be executed during various steps in the vms lifetime.",
     },
+    ivshmem => {
+	type => 'string',
+	format => $ivshmem_fmt,
+	description => "Inter-VM shared memory. Useful for direct communication between VMs, or to the host.",
+	optional => 1,
+    }
 };
 
 my $confdesc_cloudinit = {
@@ -2792,6 +2813,8 @@ sub check_local_resources {
     $loc_res = 1 if $conf->{hostusb}; # old syntax
     $loc_res = 1 if $conf->{hostpci}; # old syntax
 
+    $loc_res = 1 if $conf->{ivshmem};
+
     foreach my $k (keys %$conf) {
 	next if $k =~ m/^usb/ && ($conf->{$k} eq 'spice');
 	# sockets are safe: they will recreated be on the target side post-migrate
@@ -3892,6 +3915,24 @@ sub config_to_command {
          push @$devices, '-device', $netdevicefull;
     }
 
+    if ($conf->{ivshmem}) {
+	my $ivshmem = PVE::JSONSchema::parse_property_string($ivshmem_fmt, $conf->{ivshmem});
+	my $bus;
+	if ($q35) {
+	    $bus = print_pcie_addr("ivshmem");
+	} else {
+	    $bus = print_pci_addr("ivshmem", $bridges, $arch, $machine_type);
+	}
+	my $path = '/dev/shm/pve-shm-';
+	if ($ivshmem->{name}) {
+	    $path .= $ivshmem->{name};
+	} else {
+	    $path .= $vmid;
+	}
+	push @$devices, '-device', "ivshmem-plain,memdev=ivshmem$bus,";
+	push @$devices, '-object', "memory-backend-file,id=ivshmem,share=on,mem-path=$path,size=$ivshmem->{size}M";
+    }
+
     if (!$q35) {
 	# add pci bridges
         if (qemu_machine_feature_enabled ($machine_type, $kvmver, 2, 3)) {
@@ -5448,6 +5489,11 @@ sub vm_stop_cleanup {
 	    unlink "/var/run/qemu-server/${vmid}.$ext";
 	}
 
+	if ($conf->{ivshmem}) {
+	    my $ivshmem = PVE::JSONSchema::parse_property_string($ivshmem_fmt, $conf->{ivshmem});
+	    unlink '/dev/shm/pve-shm-' . ($ivshmem->{name} // $vmid);
+	}
+
 	foreach my $key (keys %$conf) {
 	    next if $key !~ m/^hostpci(\d+)$/;
 	    my $hostpciindex = $1;
diff --git a/PVE/QemuServer/PCI.pm b/PVE/QemuServer/PCI.pm
index f22f5ad..d847146 100644
--- a/PVE/QemuServer/PCI.pm
+++ b/PVE/QemuServer/PCI.pm
@@ -78,6 +78,7 @@ my $devices = {
     'virtio13' => { bus => 2, addr => 8 },
     'virtio14' => { bus => 2, addr => 9 },
     'virtio15' => { bus => 2, addr => 10 },
+    'ivshmem' => { bus => 2, addr => 11 },
     'virtioscsi0' => { bus => 3, addr => 1 },
     'virtioscsi1' => { bus => 3, addr => 2 },
     'virtioscsi2' => { bus => 3, addr => 3 },
@@ -150,6 +151,7 @@ sub print_pcie_addr {
 	hostpci1bus0 => { bus => "pcie.0", addr => 17 },
 	hostpci2bus0 => { bus => "pcie.0", addr => 18 },
 	hostpci3bus0 => { bus => "pcie.0", addr => 19 },
+	ivshmem => { bus => 'pcie.0', addr => 20 },
     };
 
     if (defined($devices->{$id}->{bus}) && defined($devices->{$id}->{addr})) {
-- 
2.11.0