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    SubjectRe: [PATCH v2 0/4] Implement vdpasim stop operation
    On Wed, May 25, 2022 at 4:49 AM Jason Wang <jasowang@redhat.com> wrote:
    >
    > On Wed, May 25, 2022 at 1:06 AM Eugenio Pérez <eperezma@redhat.com> wrote:
    > >
    > > Implement stop operation for vdpa_sim devices, so vhost-vdpa will offer
    > > that backend feature and userspace can effectively stop the device.
    > >
    > > This is a must before get virtqueue indexes (base) for live migration,
    > > since the device could modify them after userland gets them. There are
    > > individual ways to perform that action for some devices
    > > (VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...) but there was no
    > > way to perform it for any vhost device (and, in particular, vhost-vdpa).
    > >
    > > After the return of ioctl with stop != 0, the device MUST finish any
    > > pending operations like in flight requests. It must also preserve all
    > > the necessary state (the virtqueue vring base plus the possible device
    > > specific states) that is required for restoring in the future. The
    > > device must not change its configuration after that point.
    >
    > I'd suggest documenting this in the code maybe around ops->stop()?
    >

    I agree it'd be better to put in the source code, but both
    vdpa_config_ops and ops->stop don't have a lot of space for docs.

    Would it work to document at drivers/vdpa/vdpa.c:vhost_vdpa_stop() and
    redirect config ops like "for more info, see vhost_vdpa_stop"?

    Thanks!

    > Thanks
    >
    > >
    > > After the return of ioctl with stop == 0, the device can continue
    > > processing buffers as long as typical conditions are met (vq is enabled,
    > > DRIVER_OK status bit is enabled, etc).
    > >
    > > In the future, we will provide features similar to VHOST_USER_GET_INFLIGHT_FD
    > > so the device can save pending operations.
    > >
    > > Comments are welcome.
    > >
    > > v2:
    > > * Replace raw _F_STOP with BIT_ULL(_F_STOP).
    > > * Fix obtaining of stop ioctl arg (it was not obtained but written).
    > > * Add stop to vdpa_sim_blk.
    > >
    > > Eugenio Pérez (4):
    > > vdpa: Add stop operation
    > > vhost-vdpa: introduce STOP backend feature bit
    > > vhost-vdpa: uAPI to stop the device
    > > vdpa_sim: Implement stop vdpa op
    > >
    > > drivers/vdpa/vdpa_sim/vdpa_sim.c | 21 +++++++++++++++++
    > > drivers/vdpa/vdpa_sim/vdpa_sim.h | 1 +
    > > drivers/vdpa/vdpa_sim/vdpa_sim_blk.c | 3 +++
    > > drivers/vdpa/vdpa_sim/vdpa_sim_net.c | 3 +++
    > > drivers/vhost/vdpa.c | 34 +++++++++++++++++++++++++++-
    > > include/linux/vdpa.h | 6 +++++
    > > include/uapi/linux/vhost.h | 3 +++
    > > include/uapi/linux/vhost_types.h | 2 ++
    > > 8 files changed, 72 insertions(+), 1 deletion(-)
    > >
    > > --
    > > 2.27.0
    > >
    > >
    >

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