Am 14.07.2021 um 11:29 hat Stefan Hajnoczi geschrieben:
> v3:
> * Rebased
> v2:
> * Clarify that object-memory-memfd enables share=on by default [Marc-André]
> * Rebased
>
> vhost-user requires -object memory-backend-*,share=on option so that QEMU uses
> mmap(MAP_SHARED) on guest RAM that is shared with the vhost-user device
> backend
> process. This is needed so the QEMU process sees changes made by the
> vhost-user
> device backend process, and vice versa.
>
> Today QEMU and the vhost-user device process will start up and then fail with
> a
> confusing error message if the user forgot to specify share=on.
>
> This patch series adds a warning letting the user know that share=on is
> required.
Hmm... This seems to work when I use shared=off for the memory backend,
even though the error message is easy to miss because more error
messages follow:
$ LANG=C build/qemu-system-x86_64 -object
memory-backend-memfd,id=mem,size=1G,share=off -m 1G -M memory-backend=mem
-chardev socket,path=/tmp/vhost.sock,id=vhost1 -device
vhost-user-blk-pci,chardev=vhost1
qemu-system-x86_64: -device vhost-user-blk-pci,chardev=vhost1: warning:
Found vhost-user memory region without MAP_SHARED (did you forget -object
memory-*,share=on?)
qemu-system-x86_64: Unexpected end-of-file before all data were read
qemu-system-x86_64: Failed to set msg fds.
qemu-system-x86_64: vhost VQ 0 ring restore failed: -1: Resource
temporarily unavailable (11)
However, if I don't create the memory backend at all (which is probably
the most common error users will make), then the new message isn't
printed:
$ LANG=C build/qemu-system-x86_64 -m 1G -chardev
socket,path=/tmp/vhost.sock,id=vhost1 -device vhost-user-blk-pci,chardev=vhost1
qemu-system-x86_64: Unexpected end-of-file before all data were read
qemu-system-x86_64: Failed to set msg fds.
qemu-system-x86_64: vhost VQ 0 ring restore failed: -1: Resource
temporarily unavailable (11)
Wouldn't we want a warning for the second case, too?
Kevin
