Il mar 17 giu 2025, 18:02 Annie Li <annie.li@oracle.com> ha scritto:
Hello Paolo, On 6/16/2025 5:11 PM, Paolo Bonzini wrote:
Il lun 16 giu 2025, 21:00 Annie Li <annie.li@oracle.com> ha scritto:
My understanding of the qemu document is that it's OK to run one helper per QEMU or even per host, but multiple disks shouldn't share the same socket since it is possible that multiple commands may be sent concurrently.
Maybe QEMU has some internal lock that does the right thing and serializes requests?
Multiple disks can share the socket, the serialization of requests is handled with a mutex in scsi/pr-manager-helper.c.
Thanks a lot for the clarification.
I was only focusing on the qemu-pr-helper source code, haven't checked pr-manager-helper yet, will definitely take a look.
Hi Annie that's the part of QEMU that talks to the helper process.
Looks the following document is misleading, https://www.qemu.org/docs/master/interop/pr-helper.html Since there is a mutex handling the requests from multiple disk over one socket, I suppose the statement "It is invalid to send multiple commands concurrently on the same socket." can be removed
No, I don't think it should be removed: the mutex is exactly what makes QEMU obey that statement. Remember that the documentation is written for everyone that needs to implement a qemu-pr-helper replacement (say one that does persistent reservations using a shared database), or a client that may not be QEMU (ok in practice it will be). Paolo