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Bug 1897708

Summary: [RFE] Implement support for live attach of virtiofs device
Product: Red Hat Enterprise Linux 9 Reporter: Tom Barron <tbarron>
Component: libvirtAssignee: Ján Tomko <jtomko>
libvirt sub component: General QA Contact: Lili Zhu <lizhu>
Status: CLOSED ERRATA Docs Contact:
Severity: medium    
Priority: high CC: dgilbert, dzheng, gouthamr, jdenemar, jsuchane, jtomko, kkiwi, lmen, pkrempa, stefanha, vgoyal, virt-maint, xuzhang
Version: 9.0Keywords: FutureFeature, Triaged
Target Milestone: rcFlags: pm-rhel: mirror+
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: libvirt-7.9.0-1.el9 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2022-05-17 12:45:05 UTC Type: Feature Request
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version: 7.9.0
Embargoed:
Bug Depends On: 1897710    
Bug Blocks: 1887471    

Description Tom Barron 2020-11-13 20:40:00 UTC 
Description of problem:

  # virsh attach-device --live <domain> filesystem.xml

yields:

  error: Failed to attach device from filesystem.xml
  error: Operation not supported: live attach of device 'filesystem' is not supported

whereas:

  # virsh attach-device --persistent <domain> filesystem.xml

works and with subsequent 'virsh start' of the domain and an accompanying virtiofsd process sharing between host and guest works fine.

Version-Release number of selected component (if applicable):

[test@osp-storage-04 ~]$ virsh --version
6.0.0


How reproducible:

100%

Steps to Reproduce:
1.  Define a domain with shared memory backing and numa topology as at https://libvirt.org/kbase/virtiofs.html
2.  virsh start the guest VM
3.  attempt 'virsh attach-device --live <domain> filesystem.xml' with appropriate XML device configuration as described at the just-mentioned Kbase.

Actual results:

Error message as reported.

Expected results:  Successful hot-plug attach of the virtiofs files sytem to the running guest.

Would expect corresponding 'virsh detatch-device --live ...' commands to work as well.

Additional info:

We need this to work for OpenStack Nova to support virtiofs devices.
Comment 1 Tom Barron 2020-11-13 22:02:56 UTC 
Please note that I reported libvirt 6.0.0 above testing on Red Hat Enterprise Linux release 8.4 Beta (Ootpa) but I get the same result attempting --live device-attach on 6.6.0 running on Fedora release 33 (Thirty Three)
Comment 3 Ademar Reis 2020-11-17 21:34:45 UTC 
*** Bug 1897710 has been marked as a duplicate of this bug. ***
Comment 4 Vivek Goyal 2021-01-21 19:01:36 UTC 
I tried a device hot add of virtiofs device with qemu and it worked. So it looks like that lower layer pieces are in place and support will need to be added to virsh/libvirt.

To keep it simple, I booted a VM with qemu directly. First I hot removed a virtiofs device.

$(monitor) device_del myvirtiofs

And then re-added it back. 

$(monitor) device_add vhost-user-fs-pci,bus=root1,id=myvirtiofs,chardev=char0,tag=myfs,queue-size=1024,cache-size=16G

And it works. All this while virtiofs daemon is already running.
Comment 5 Vivek Goyal 2021-05-03 13:28:19 UTC 
Supporting vhost-user-fs-pci device hot add/remove is also important from live migration point of view. We don't have full support for live migration, so current workaround is that hot remove virtiofs device on source and then hot add it back on destination. So from that perspective also it will be nice to have this support added to libvirt.

https://listman.redhat.com/archives/virtio-fs/2021-May/msg00002.html
Comment 8 Ján Tomko 2021-10-06 07:20:04 UTC 
v1 proposed upstream:
https://listman.redhat.com/archives/libvir-list/2021-October/msg00097.html
Comment 9 Ján Tomko 2021-10-12 12:44:08 UTC 
commit b98787303498cfb8426ab27ee62247b164101242
Author:     Ján Tomko <jtomko>
CommitDate: 2021-10-12 14:41:13 +0200

    qemu: implement virtiofs hotplug
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1897708
    
    Signed-off-by: Ján Tomko <jtomko>
    Reviewed-by: Peter Krempa <pkrempa>

git describe: v7.8.0-182-gb987873034
Comment 10 Lili Zhu 2021-11-08 09:56:21 UTC 
Tested with libvirt-7.9.0-1.fc36.x86_64:

1 start a guest with shared memory
 <memoryBacking>
    <access mode='shared'/>
  </memoryBacking>

2. create dir
# mkdir /path2

3. prepare xml snippet
# cat filesystem.xml 
<filesystem type='mount' accessmode='passthrough'>
      <driver type='virtiofs'/>
      <binary path='/usr/libexec/virtiofsd' xattr='on'>
        <cache mode='always'/>
        <lock posix='on' flock='on'/>
      </binary>
      <source dir='/path2'/>
      <target dir='mount_tag2'/>
      <address type='pci' domain='0x0000' bus='0x08' slot='0x00' function='0x0'/>
    </filesystem>

4. attach device
# virsh attach-device avocado-vt-vm1 filesystem.xml 
Device attached successfully

5. mount virtiofs in guest
[In guest]#mkdir /mount2; mount -t virtiofs mount_tag2 /mount2
6. try to write something
[In guest]# dd if=/dev/random of=testfile bs=1M count=1024

7. umount fs, then detach virtiofs device
# virsh detach-device avocado-vt-vm1 filesystem.xml 
Device detached successfully

8. check guest xml
# virsh dumpxml avocado-vt-vm1 |grep filesystem
(no output)
Comment 14 Lili Zhu 2021-11-18 05:52:14 UTC 
Verify this bug with:
libvirt-7.9.0-1.el9.x86_64
qemu-kvm-6.1.0-6.el9.x86_64

Please refer to Comment #10 for verification steps. As the testing results match with the expected reuslts, mark the bug as verified.
Comment 16 errata-xmlrpc 2022-05-17 12:45:05 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (new packages: libvirt), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2022:2390