Hi, thanks for your reply On Fri, Oct 24, 2025 at 9:53 AM Jason Wang <[email protected]> wrote: > > On Thu, Oct 23, 2025 at 10:34 AM Zhang Tianci > <[email protected]> wrote: > > > > Hi, thank you for your reply, but I still have a few questions: > > > > On Wed, Oct 22, 2025 at 7:31 PM Michael S. Tsirkin <[email protected]> wrote: > > > > > > On Wed, Oct 22, 2025 at 07:21:45PM +0800, Zhang Tianci wrote: > > > > Hi, > > > > I noticed that the reference count of the virtio_pci kernel module > > > > in the VM is always 0, even though there are at least two > > > > virtio block devices and one virtiofs device in the VM. > > > > > > > > Using rmmod virtio_pci can unload the virtio_pci module, > > > > but this renders the virtio block devices unusable. > > > > > > it removes them. you can put it back in and you will > > > get devices again. > > > > But I can't do it anymore because the rootfs is no longer available, > > or rather, the OS is no longer available. > > > > > > > > > I wonder if this result is expected? Why don't the virtio block devices > > > > and virtiofs device hold a reference count to the virtio_pci kernel > > > > module? > > > > > > because they don't have to. > > > > Is it due to design reasons or implementation reasons? > > Is it because the semantics of kernel module refcnt does not include such > > logical dependency? > > Note that virito has a bus so it follows the device/driver model so if > I was not wrong the refcnt was handled by the driver core.
Let's look at an example: $ lsmod | grep virtio virtio_balloon 20480 0 virtio_console 40960 1 virtiofs 32768 1 <- one virtiofs fuse 172032 2 virtiofs virtio_net 73728 0 net_failover 20480 1 virtio_net virtio_blk 32768 2 <- two block devices virtio_pci 24576 0 virtio_pci_legacy_dev 16384 1 virtio_pci virtio_pci_modern_dev 16384 1 virtio_pci virtio 16384 6 virtio_console,virtio_balloon,virtiofs,virtio_pci,virtio_blk,virtio_net virtio_ring 49152 6 virtio_console,virtio_balloon,virtiofs,virtio_pci,virtio_blk,virtio_net There are two virtio_blk devices which are vda and vdb, and one virtiofs device. We can find the block device and fs instance are holding virtio_blk and virtiofs' refcnts. But they don't hold virtio_pci(pci bus) or virtio(virtio bus) refcnts even though they logically depend on them. So I might need to consult the driver core maintainers?(I have cc'd them in this email.) Thanks, Tianci
