Re: [Qemu-devel] [PATCH for-2.7 v5 0/2] vhost-user: Extend protocol to receive replies on any command.

[Prerna]

Pl ignore the above series, sending a new revision.

On Thu, Jul 28, 2016 at 11:52 AM, Prerna Saxena <address@hidden>
wrote:

> From: Prerna Saxena <address@hidden>
>
>
> vhost-user: Extend protocol to receive replies on any command.
>
> The current vhost-user protocol requires the client to send reply to only a
> few commands. For the remaining commands, it is impossible for QEMU to
> know the
> status of the requested operation -- ie, did it succeed? If so, by what
> time?
>
> This is inconvenient, and can also lead to races. As an example:
>
> (1) Qemu sends a SET_MEM_TABLE to the backend (eg, a vhost-user net
> application).Note that SET_MEM_TABLE does not require a reply according to
> the spec.
> (2) Qemu commits the memory to the guest.
> (3) Guest issues an I/O operation over a new memory region which was
> configured on (1).
> (4) The application hasn't yet remapped the memory, but it sees the I/O
> request.
> (5) The application cannot satisfy the request because it does not know
> about those GPAs.
>
> Note that the kernel implementation does not suffer from this limitation
> since messages are sent via an ioctl(). The ioctl() blocks until the
> backend (eg. vhost-net) completes the command and returns (with an error
> code).
>
> Changing the behaviour of current vhost-user commands would break existing
> applications.
> Patch 1 introduces a protocol extension, VHOST_USER_PROTOCOL_F_REPLY_ACK.
> This
> feature, if negotiated, allows QEMU to request a reply to any message by
> setting
> the newly introduced "need_reply" flag. The application must then respond
> to qemu
> by providing a status about the requested operation.
>
> Patch 2 adds a workaround for the race described above for clients that do
> not support REPLY_ACK
> feature. It introduces  a get_features command to be sent before returning
> from set_mem_table. While this is not a complete fix, it will help client
> applications that strictly process messagesin order.
>
> Changelog:
> ----------
> Changes v4->v5:
> 1) Patch 1 :
> * Reword 'response' to 'reply' on public demand.
> * Documentation is more concise.
> Patch 2 : unchanged
>
> Changes v3->v4:
> 1) Rearranged code in PATCH 1 to offset compiler warnings about missing
> declaration of vhost_user_read(). Fixed by moving process_message_reply()
> after definition of vhost_user_read()
> 2) Fixed minor suggestions in writeup for this protocol extension.
>
> Changes v2->v3:
> 1) Swapped the patch numbers 1 & 2 from the previous series.
> 2) Patch 1 (previously patch 2 in v2): addresses MarcAndre's review
> comments and renames function 'process_message_response' to
> 'process_message_reply'
> 3) Patch 2 (ie patch 1 in v2) : Unchanged from v2.
>
> Changes v1->v2:
> 1) Patch 1 : Ask for get_features before returning from set_mem_table(new).
> 2) Patch 2 : * Improve documentation.
>           * Abstract out commonly used operations in the form of a
> function, process_message_response(). Also implement this only for
> SET_MEM_TABLE.
>
> References:
> v1 : https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg07152.html
> v2 : https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg00048.html
> v3 : https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg01598.html
> v4 : https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg06173.html
>
> Prerna Saxena (2):
>   vhost-user: Introduce a new protocol feature REPLY_ACK.
>   vhost-user: Attempt to fix a race with set_mem_table.
>
>  docs/specs/vhost-user.txt |  44 +++++++++++++++
>  hw/virtio/vhost-user.c    | 133
> ++++++++++++++++++++++++++++++----------------
>  2 files changed, 130 insertions(+), 47 deletions(-)
>
> --
> 1.8.1.2
>
>
> Prerna Saxena (2):
>   vhost-user: Introduce a new protocol feature REPLY_ACK.
>   vhost-user: Attempt to fix a race with set_mem_table.
>
>  docs/specs/vhost-user.txt |  26 +++++++++
>  hw/virtio/vhost-user.c    | 132
> +++++++++++++++++++++++++++++-----------------
>  2 files changed, 111 insertions(+), 47 deletions(-)
>
> --
> 1.8.1.2
>
> Prerna Saxena (2):
>   vhost-user: Introduce a new protocol feature REPLY_ACK.
>   vhost-user: Attempt to fix a race with set_mem_table.
>
>  docs/specs/vhost-user.txt |  26 +++++++++
>  hw/virtio/vhost-user.c    | 132
> +++++++++++++++++++++++++++++-----------------
>  2 files changed, 111 insertions(+), 47 deletions(-)
>
> --
> 1.8.1.2
>
>