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    SubjectRe: [PATCH v4 0/4] Implement vdpasim stop operation
    On Thu, May 26, 2022 at 02:43:34PM +0200, Eugenio Pérez 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.
    >
    > 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.


    So given this is just for simulator and affects UAPI I think it's fine
    to make it wait for the next merge window, until there's a consensus.
    Right?

    > v4:
    > * Replace VHOST_STOP to VHOST_VDPA_STOP in vhost ioctl switch case too.
    >
    > v3:
    > * s/VHOST_STOP/VHOST_VDPA_STOP/
    > * Add documentation and requirements of the ioctl above its definition.
    >
    > 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 | 14 ++++++++++++
    > include/uapi/linux/vhost_types.h | 2 ++
    > 8 files changed, 83 insertions(+), 1 deletion(-)
    >
    > --
    > 2.31.1
    >

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