Pl ignore the above series, sending a new revision. On Thu, Jul 28, 2016 at 11:52 AM, Prerna Saxena <saxenap....@gmail.com> wrote:
> From: Prerna Saxena <prerna.sax...@nutanix.com> > > > 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 > >
