[pbs-devel] [PATCH proxmox-backup 4/9] file-restore: support more drives

[Stefan Reiter <s.reiter@proxmox.com>]

A PCI bus can only support up to 32 devices, so excluding built-in
devices that left us with a maximum of about 25 drives. By adding a new
PCI bridge every 32 devices (starting at bridge ID 2 to avoid conflicts
with automatic bridges), we can theoretically support up to 8096 drives.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---

Tested with a 41 disk VM, the most I could force into a PVE config.

 src/bin/proxmox_file_restore/qemu_helper.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/bin/proxmox_file_restore/qemu_helper.rs b/src/bin/proxmox_file_restore/qemu_helper.rs
index 9b44b55d..c9d816ca 100644
--- a/src/bin/proxmox_file_restore/qemu_helper.rs
+++ b/src/bin/proxmox_file_restore/qemu_helper.rs
@@ -217,10 +217,21 @@ pub async fn start_vm(
             "file=pbs:repository={},,snapshot={},,archive={}{},read-only=on,if=none,id=drive{}",
             details.repo, details.snapshot, file, keyfile, id
         ));
+
+        // a PCI bus can only support 32 devices, so add a new one every 32
+        let bus = (id / 32) + 2;
+        if id % 32 == 0 {
+            drives.push("-device".to_owned());
+            drives.push(format!("pci-bridge,id=bridge{},chassis_nr={}", bus, bus));
+        }
+
         drives.push("-device".to_owned());
         // drive serial is used by VM to map .fidx files to /dev paths
         let serial = file.strip_suffix(".img.fidx").unwrap_or(&file);
-        drives.push(format!("virtio-blk-pci,drive=drive{},serial={}", id, serial));
+        drives.push(format!(
+            "virtio-blk-pci,drive=drive{},serial={},bus=bridge{}",
+            id, serial, bus
+        ));
         id += 1;
     }
 
-- 
2.20.1