Re: [Virtio-fs] vhost_set_vring_kick failed

From: Sergio Lopez <slp@redhat.com>
To: "Pra.. Dew.." <linux_learner@outlook.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	"virtio-fs@redhat.com" <virtio-fs@redhat.com>,
	"gmaglione@redhat.com" <gmaglione@redhat.com>,
	Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [Virtio-fs] vhost_set_vring_kick failed
Date: Tue, 31 May 2022 12:50:50 +0200	[thread overview]
Message-ID: <20220531104953.3lpjjpuxepc7wwdg@mhamilton> (raw)
In-Reply-To: <BY5PR14MB3893C17AAED9ECD7280AE7FD86D99@BY5PR14MB3893.namprd14.prod.outlook.com>

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On Thu, May 26, 2022 at 04:07:36PM +0000, Pra.. Dew.. wrote:
> Thanks for the response.  The  version of the qemu is 5.1.0 and  here is the comandline..
> 
> 
> [/usr/bin/qemu-system-test-machine test --enable-kvm -display none -mon mon-console,mode=readline -chardev socket,host=,port=5001,server,nowait,id=mon-console -device virtio-serial-device,max_ports=2 -device virtconsole,chardev=console,name=console -chardev socket,host=,port=5000,server,nowait,id=console -netdev tap,id=tap0,ifname=tap0,vhost=on,script=no,downscript=no -device virtio-net-device,netdev=tap0 -device vhost-vsock-device,guest-cid=4 -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-device,rng=rng0 -chardev socket,id=char0,path=/run/vm001-vhost-fs.sock -device vhost-user-fs-device,queue-size=2,chardev=char0,tag=myfs -object memory-backend-memfd,id=mem,size=4G,share=on -kernel /var/lib/are/images/active/kernel.bin -dtb /var/lib/are/images/active/device-tree.dtb -device virtio-blk-device,drive=writable,serial=writable -drive file=/var/lib/are/volumes/writable.bin,if=none,id=writable,format=raw -device virtio-blk-device,drive=rootfs,serial=rootfs -drive file=/var/lib/are/images/active/rootfs/rootfs.bin,if=none,id=rootfs,format=raw,readonly]

Thanks for the details. I knew that we didn't support older versions,
but didn't want to reply that without explaining why.

I've just took a look, and the origin of this incompatibility is this
change in "hw/virtio/vhost-user.c":

qemu-5.1.0:

typedef struct VhostUserMemRegMsg {
    uint32_t padding;
    VhostUserMemoryRegion region;
} VhostUserMemRegMsg;

qemu-upstream (since 3009edff8192991293fe9e2b50b0d90db83c4a89):

typedef struct VhostUserMemRegMsg {
    uint64_t padding;
    VhostUserMemoryRegion region;
} VhostUserMemRegMsg;

Note how "padding" has changed from uint32_t to uint64_t.

This means we only support QEMU versions starting 5.2.0.

Regards,
Sergio.

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