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Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for cl
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands. |
Date: |
Sat, 25 Jun 2016 01:43:33 +0300 |
On Fri, Jun 24, 2016 at 01:17:07AM -0700, Prerna Saxena wrote:
> From: Prerna Saxena <address@hidden>
>
> The current vhost-user protocol requires the client to send responses to only
> few commands. For the remaining commands, it is impossible for QEMU to know
> the status of the requested operation -- ie, did it succeed at all, and if
> so, at 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) and SET_MEM_TABLE doesn't 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 doesn't know about
> those GPAs
OK, but there's a simple way to fix the race: submit
another request e.g. GET_FEATURES and wait for a response.
>
> 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. This patch introduces a protocol extension,
> VHOST_USER_PROTOCOL_F_REPLY_ACK. This feature, if negotiated, allows QEMU to
> annotate messages to the application that it seeks a response for. The
> application must then respond to qemu by providing a status about the
> requested operation.
I would like this structured like this:
1. fix races by sending GET_FEATURES and waiting for it
2. add VHOST_USER_PROTOCOL_F_REPLY_ACK
>
> Prerna Saxena (1):
> vhost-user : Introduce a new feature, VHOST_USER_PROTOCOL_F_REPLY_ACK
> This feature, if negotiated, forces the remote vhost-user
> process to send a u64 reply containin status code for each
> requested operation.
> Status codes are '0' for success, and non-zero for error.
>
> docs/specs/vhost-user.txt | 36 +++++++++++
> hw/virtio/vhost-user.c | 153
> +++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 186 insertions(+), 3 deletions(-)
>
> --
> 1.8.1.2
>
- Re: [Qemu-devel] [PATCH 1/1] vhost-user : Introduce a new feature VHOST_USER_PROTOCOL_F_REPLY_ACK. This feature, if negotiated, forces the remote vhost-user process to send a u64 reply containing a status code for each requested operation. Status codes are '0' for success, and non-zero for error., (continued)
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Prerna, 2016/06/24
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Marc-André Lureau, 2016/06/24
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Felipe Franciosi, 2016/06/24
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Prerna Saxena, 2016/06/24
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Michael S. Tsirkin, 2016/06/24
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Prerna Saxena, 2016/06/24
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Michael S. Tsirkin, 2016/06/25
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Prerna Saxena, 2016/06/26
- Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands., Michael S. Tsirkin, 2016/06/25
Re: [Qemu-devel] [PATCH 0/1] vhost-user: Add a protocol extension for client responses to vhost commands.,
Michael S. Tsirkin <=