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[Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received

Jens Freimann posted 5 patches 8 years, 6 months ago
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[Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received
Posted by Jens Freimann 8 years, 6 months ago 
From: Jens Freimann <jfreiman@redhat.com>

End processing of messages when VHOST_USER_NONE
is received.

Without this we run into a vubr_panic() call and get
"PANIC: Unhandled request: 0"

Signed-off-by: Jens Freimann <jfreiman@redhat.com>
---
 contrib/libvhost-user/libvhost-user.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 9efb9dac0e..35fa0c5e56 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -161,7 +161,7 @@ vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
         rc = recvmsg(conn_fd, &msg, 0);
     } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
 
-    if (rc <= 0) {
+    if (rc < 0) {
         vu_panic(dev, "Error while recvmsg: %s", strerror(errno));
         return false;
     }
@@ -806,6 +806,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         return vu_get_queue_num_exec(dev, vmsg);
     case VHOST_USER_SET_VRING_ENABLE:
         return vu_set_vring_enable_exec(dev, vmsg);
+    case VHOST_USER_NONE:
+        break;
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);
-- 
2.13.3
Re: [Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received
Posted by Marc-André Lureau 8 years, 4 months ago 
Hi

On Tue, Aug 8, 2017 at 10:52 PM Jens Freimann <jfreimann@redhat.com> wrote:
>
> From: Jens Freimann <jfreiman@redhat.com>
>
> End processing of messages when VHOST_USER_NONE
> is received.
>
> Without this we run into a vubr_panic() call and get
> "PANIC: Unhandled request: 0"
>
> Signed-off-by: Jens Freimann <jfreiman@redhat.com>
> ---
>  contrib/libvhost-user/libvhost-user.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
> index 9efb9dac0e..35fa0c5e56 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -161,7 +161,7 @@ vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
>          rc = recvmsg(conn_fd, &msg, 0);
>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>
> -    if (rc <= 0) {
> +    if (rc < 0) {
>          vu_panic(dev, "Error while recvmsg: %s", strerror(errno));
>          return false;
>      }
> @@ -806,6 +806,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
>          return vu_get_queue_num_exec(dev, vmsg);
>      case VHOST_USER_SET_VRING_ENABLE:
>          return vu_set_vring_enable_exec(dev, vmsg);
> +    case VHOST_USER_NONE:
> +        break;


I am afraid this isn't working. vu_message_read() returns
true/success, vu_process_message() returns false/no-reply, so
vu_dispatch() will return success, and the caller has no clear way to
know that the socket got disconnected. For me the vu_panic() was quite
more appropriate here.

What problem did this patch exactly solve?

>
>      default:
>          vmsg_close_fds(vmsg);
>          vu_panic(dev, "Unhandled request: %d", vmsg->request);
> --
> 2.13.3
>
>
Re: [Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received
Posted by Jens Freimann 8 years, 4 months ago 
On Tue, Sep 19, 2017 at 04:46:24PM +0000, Marc-Andr?? Lureau wrote:
>Hi
>
>On Tue, Aug 8, 2017 at 10:52 PM Jens Freimann <jfreimann@redhat.com> wrote:
>>
>> From: Jens Freimann <jfreiman@redhat.com>
>>
>> End processing of messages when VHOST_USER_NONE
>> is received.
>>
>> Without this we run into a vubr_panic() call and get
>> "PANIC: Unhandled request: 0"
>>
>> Signed-off-by: Jens Freimann <jfreiman@redhat.com>
>> ---
>>  contrib/libvhost-user/libvhost-user.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
>> index 9efb9dac0e..35fa0c5e56 100644
>> --- a/contrib/libvhost-user/libvhost-user.c
>> +++ b/contrib/libvhost-user/libvhost-user.c
>> @@ -161,7 +161,7 @@ vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
>>          rc = recvmsg(conn_fd, &msg, 0);
>>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>>
>> -    if (rc <= 0) {
>> +    if (rc < 0) {
>>          vu_panic(dev, "Error while recvmsg: %s", strerror(errno));
>>          return false;
>>      }
>> @@ -806,6 +806,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
>>          return vu_get_queue_num_exec(dev, vmsg);
>>      case VHOST_USER_SET_VRING_ENABLE:
>>          return vu_set_vring_enable_exec(dev, vmsg);
>> +    case VHOST_USER_NONE:
>> +        break;
>
>
>I am afraid this isn't working. vu_message_read() returns
>true/success, vu_process_message() returns false/no-reply, so
>vu_dispatch() will return success, and the caller has no clear way to
>know that the socket got disconnected. For me the vu_panic() was quite
>more appropriate here.
>
>What problem did this patch exactly solve?

The problem was that a VhostUserMsg of size 0 is considered an
error. But recvmsg() can return 0. When I ran my pxe
testcase using vhost-user-bridge I ran into vu_panic() because of this. 

This worked because VHOST_USER_NONE is defined as 0. Instead of
doing this we could just allow a vmsg size of zero and not tread it
as an error?


regards,
Jens
Re: [Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received
Posted by Marc-André Lureau 8 years, 4 months ago 
On Wed, Sep 20, 2017 at 5:09 PM, Jens Freimann <jfreimann@redhat.com> wrote:
> On Tue, Sep 19, 2017 at 04:46:24PM +0000, Marc-Andr?? Lureau wrote:
>>
>> Hi
>>
>> On Tue, Aug 8, 2017 at 10:52 PM Jens Freimann <jfreimann@redhat.com>
>> wrote:
>>>
>>>
>>> From: Jens Freimann <jfreiman@redhat.com>
>>>
>>> End processing of messages when VHOST_USER_NONE
>>> is received.
>>>
>>> Without this we run into a vubr_panic() call and get
>>> "PANIC: Unhandled request: 0"
>>>
>>> Signed-off-by: Jens Freimann <jfreiman@redhat.com>
>>> ---
>>>  contrib/libvhost-user/libvhost-user.c | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/contrib/libvhost-user/libvhost-user.c
>>> b/contrib/libvhost-user/libvhost-user.c
>>> index 9efb9dac0e..35fa0c5e56 100644
>>> --- a/contrib/libvhost-user/libvhost-user.c
>>> +++ b/contrib/libvhost-user/libvhost-user.c
>>> @@ -161,7 +161,7 @@ vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg
>>> *vmsg)
>>>          rc = recvmsg(conn_fd, &msg, 0);
>>>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>>>
>>> -    if (rc <= 0) {
>>> +    if (rc < 0) {
>>>          vu_panic(dev, "Error while recvmsg: %s", strerror(errno));
>>>          return false;
>>>      }
>>> @@ -806,6 +806,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
>>>          return vu_get_queue_num_exec(dev, vmsg);
>>>      case VHOST_USER_SET_VRING_ENABLE:
>>>          return vu_set_vring_enable_exec(dev, vmsg);
>>> +    case VHOST_USER_NONE:
>>> +        break;
>>
>>
>>
>> I am afraid this isn't working. vu_message_read() returns
>> true/success, vu_process_message() returns false/no-reply, so
>> vu_dispatch() will return success, and the caller has no clear way to
>> know that the socket got disconnected. For me the vu_panic() was quite
>> more appropriate here.
>>
>> What problem did this patch exactly solve?
>
>
> The problem was that a VhostUserMsg of size 0 is considered an
> error. But recvmsg() can return 0. When I ran my pxe

When did recvmsg() return 0? It should only be called after a poll
IN/ERR, in case of data it should always return != 0, and if
disconnected, it returns 0.

> testcase using vhost-user-bridge I ran into vu_panic() because of this.
> This worked because VHOST_USER_NONE is defined as 0. Instead of
> doing this we could just allow a vmsg size of zero and not tread it
> as an error?

We want to treat disconnect as a panic condition imho, that the
library user is free to implement in different way (abort() clean
exit, reconnect etc).

Please explain your use case and how you ran into recvmsg() = 0 and
what you expect to happen at this point.

-- 
Marc-André Lureau
Re: [Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received
Posted by Jens Freimann 8 years, 4 months ago 
On Wed, Sep 20, 2017 at 04:14:33PM +0000, Marc-Andr?? Lureau wrote:
>On Wed, Sep 20, 2017 at 5:09 PM, Jens Freimann <jfreimann@redhat.com> wrote:
>> On Tue, Sep 19, 2017 at 04:46:24PM +0000, Marc-Andr?? Lureau wrote:
>>>
>>> Hi
>>>
>>> On Tue, Aug 8, 2017 at 10:52 PM Jens Freimann <jfreimann@redhat.com>
>>> wrote:
>>>>
>>>>
>>>> From: Jens Freimann <jfreiman@redhat.com>
>>>>
>>>> End processing of messages when VHOST_USER_NONE
>>>> is received.
>>>>
>>>> Without this we run into a vubr_panic() call and get
>>>> "PANIC: Unhandled request: 0"
>>>>
>>>> Signed-off-by: Jens Freimann <jfreiman@redhat.com>
>>>> ---
>>>>  contrib/libvhost-user/libvhost-user.c | 4 +++-
>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/contrib/libvhost-user/libvhost-user.c
>>>> b/contrib/libvhost-user/libvhost-user.c
>>>> index 9efb9dac0e..35fa0c5e56 100644
>>>> --- a/contrib/libvhost-user/libvhost-user.c
>>>> +++ b/contrib/libvhost-user/libvhost-user.c
>>>> @@ -161,7 +161,7 @@ vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg
>>>> *vmsg)
>>>>          rc = recvmsg(conn_fd, &msg, 0);
>>>>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>>>>
>>>> -    if (rc <= 0) {
>>>> +    if (rc < 0) {
>>>>          vu_panic(dev, "Error while recvmsg: %s", strerror(errno));
>>>>          return false;
>>>>      }
>>>> @@ -806,6 +806,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
>>>>          return vu_get_queue_num_exec(dev, vmsg);
>>>>      case VHOST_USER_SET_VRING_ENABLE:
>>>>          return vu_set_vring_enable_exec(dev, vmsg);
>>>> +    case VHOST_USER_NONE:
>>>> +        break;
>>>
>>>
>>>
>>> I am afraid this isn't working. vu_message_read() returns
>>> true/success, vu_process_message() returns false/no-reply, so
>>> vu_dispatch() will return success, and the caller has no clear way to
>>> know that the socket got disconnected. For me the vu_panic() was quite
>>> more appropriate here.
>>>
>>> What problem did this patch exactly solve?
>>
>>
>> The problem was that a VhostUserMsg of size 0 is considered an
>> error. But recvmsg() can return 0. When I ran my pxe
>
>When did recvmsg() return 0? It should only be called after a poll
>IN/ERR, in case of data it should always return != 0, and if
>disconnected, it returns 0.

My usecase is that my testcase starts a pxeboot data transfer that
goes through vhost-user-bridge. When the transfer is done the socket
is disconnected and recvmsg() returns 0. I want vhost-user-bridge to
end gracefully, without spitting out an error message. Is that
reasonable? 
>
>> testcase using vhost-user-bridge I ran into vu_panic() because of this.
>> This worked because VHOST_USER_NONE is defined as 0. Instead of
>> doing this we could just allow a vmsg size of zero and not tread it
>> as an error?
>
>We want to treat disconnect as a panic condition imho, that the
>library user is free to implement in different way (abort() clean
>exit, reconnect etc).

Ok, that wasn't obvious to me. Thanks for clarifying! 
So I was "fixing" the wrong part. On a disconnect vubr_panic() in
vhost-user-bridge.c is called and is supposed to do the right thing. 

Currently it will print an error message "PANIC: Unhandled request:
0" in my use case. I could ignore that or check for exactly this
string and suppress the error message. Both seems a bit ugly to me...

>
>Please explain your use case and how you ran into recvmsg() = 0 and
>what you expect to happen at this point.

Hope this helps! Looks like we can revert this patch. I'll send a
patch to do this.  

regards,
Jens
Re: [Qemu-devel] [PATCH v2 3/5] libvhost-user: quit when no more data received
Posted by Jens Freimann 8 years, 4 months ago 
On Thu, Sep 21, 2017 at 01:31:37PM +0000, Jens Freimann wrote:
>On Wed, Sep 20, 2017 at 04:14:33PM +0000, Marc-Andr?? Lureau wrote:
>>On Wed, Sep 20, 2017 at 5:09 PM, Jens Freimann <jfreimann@redhat.com> wrote:
>>>On Tue, Sep 19, 2017 at 04:46:24PM +0000, Marc-Andr?? Lureau wrote:
>>>>On Tue, Aug 8, 2017 at 10:52 PM Jens Freimann <jfreimann@redhat.com>
>>>>wrote:
>>We want to treat disconnect as a panic condition imho, that the
>>library user is free to implement in different way (abort() clean
>>exit, reconnect etc).
>
>Ok, that wasn't obvious to me. Thanks for clarifying! So I was 
>"fixing" the wrong part. On a disconnect vubr_panic() in
>vhost-user-bridge.c is called and is supposed to do the right thing.
>
>Currently it will print an error message "PANIC: Unhandled request:

Actually it is "Error while recvmsg" because in vu_message_read()
vu_panic is called if rc from recvmsg is <= 0. Followed by "Error
while dispatching" printed by vhost-user-bridge. 

regards,
Jens

Patchew 2.1-devel-b67e4c2

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