[SPDK] vhost is destroyed many times when starting vhost device

Hi,

In rte_vhost_compat.c, spdk_extern_vhost_pre_msg_handler will call
destroy_device when some conditions meet.

I tested and found when a vhost-blk setup, the vhost device will be
destroyed 9 times.
And the bdev(no matter which type) will be affected. I'm using the aio
bdev, and the io_setup/io_destroy will be called 9 times when a disk
is inserted to a VM.

My concern is:
Is there any solution to reduce the call times(at least: disks nums * 9)?
The call will slow down the VM boot time if VM has multiple disks.
There are some  related logs:

Starting SPDK v20.01-pre git sha1 93eecf627 / DPDK 19.11.0 initialization...
[ DPDK EAL parameters: spdk_tgt --no-shconf -c 1 -m 1
--log-level=lib.eal:6 --log-level=lib.cryptodev:5 --log-level=user1:6
--iova-mode=pa --base-virtaddr=0x200000000000 --match-allocations
--file-prefix=spdk_pid2004865 ]
EAL: No available hugepages reported in hugepages-1048576kB
app.c: 645:spdk_app_start: *NOTICE*: Total cores available: 1
reactor.c: 346:_spdk_reactor_run: *NOTICE*: Reactor started on core 0
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 174:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 193:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup
rte_vhost_compat.c: 225:spdk_extern_vhost_pre_msg_handler: *ERROR*:
destroy device
rte_vhost_compat.c: 130:stop_device: *ERROR*: call stop_device
bdev_aio.c: 581:bdev_aio_group_destroy_cb: *ERROR*:  call io_destroy
bdev_aio.c: 563:bdev_aio_group_create_cb: *ERROR*:  call io_setup

Thanks,

Feng Li

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