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From: Juergen Gross <jgross@suse.com>
To: Julien Grall <julien@xen.org>, xen-devel@lists.xenproject.org
Cc: raphning@amazon.co.uk, doebel@amazon.de,
	Julien Grall <jgrall@amazon.com>,
	Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH 08/10] tools/xenstored: Extend restore code to handle multiple input buffer
Date: Thu, 24 Jun 2021 11:20:34 +0200	[thread overview]
Message-ID: <5d641d86-53ce-27d6-6a54-c58d85164204@suse.com> (raw)
In-Reply-To: <c6ad91cd-f531-5c19-e246-bb8c4ce304f2@xen.org>


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On 24.06.21 10:42, Julien Grall wrote:
> Hi Juergen,
> 
> On 24/06/2021 10:30, Juergen Gross wrote:
>> On 16.06.21 16:43, Julien Grall wrote:
>>> From: Julien Grall <jgrall@amazon.com>
>>>
>>> Currently, the restore code is considering the stream will contain at
>>> most one in-flight request per connection. In a follow-up changes, we
>>> will want to transfer multiple in-flight requests.
>>>
>>> The function read_state_buffered() is now extended to restore multiple
>>> in-flight request. Complete requests will be queued as delayed
>>> requests, if there a partial request (only the last one can) then it
>>> will used as the current in-flight request.
>>>
>>> Note that we want to bypass the quota check for delayed requests as
>>> the new Xenstore may have a lower limit.
>>>
>>> Lastly, there is no need to change the specification as there was
>>> no restriction on the number of in-flight requests preserved.
>>>
>>> Signed-off-by: Julien Grall <jgrall@amazon.com>
>>> ---
>>>   tools/xenstore/xenstored_core.c | 56 ++++++++++++++++++++++++++++-----
>>>   1 file changed, 48 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/tools/xenstore/xenstored_core.c 
>>> b/tools/xenstore/xenstored_core.c
>>> index a5084a5b173d..5b7ab7f74013 100644
>>> --- a/tools/xenstore/xenstored_core.c
>>> +++ b/tools/xenstore/xenstored_core.c
>>> @@ -1486,6 +1486,10 @@ static void process_message(struct connection 
>>> *conn, struct buffered_data *in)
>>>       enum xsd_sockmsg_type type = in->hdr.msg.type;
>>>       int ret;
>>> +    /* At least send_error() and send_reply() expects 
conn->in == in */
>>> +    assert(conn->in == in);
>>> +    trace_io(conn, in, 0);
>>> +
>>>       if ((unsigned int)type >= XS_TYPE_COUNT|| !wire_funcs[type].func) 
>> {
>>>           eprintf("Client unknown operation %i", type);
>>>           send_error(conn, ENOSYS);
>>> @@ -1515,6 +1519,23 @@ static void process_message(struct connection 
>>> *conn, struct buffered_data *in)
>>>       conn->transaction = NULL;
>>>   }
>>> +static bool process_delayed_message(struct delayed_request *req)
>>> +{
>>> +    struct connection *conn = req->data;
>>> +    struct buffered_data *saved_in = conn->in;
>>> +
>>> +    /*
>>> +     * Part of process_message() expects conn->in to contains the
>>> +     * processed response. So save the current conn->in and restore it
>>> +     * afterwards.
>>> +     */
>>> +    conn->in = req->in;
>>> +    process_message(req->data, req->in);
>>> +    conn->in = saved_in;
>>
>> This pattern was added to do_lu_start() already, and it will be needed
>> for each other function being called via call_delayed().
>>
>> Maybe it would be better to add conn explicitly to struct
>> delayed_request (or even better: replace data with conn) and to do the
>> conn->in saving/setting/restoring in call_delayed() instead?
> 
> This was my original approach, but I abandoned it because in the case of 
> do_lu_start() we need to save the original conn->in in the stream (see 
> patch #3 for more details).
> 
> If we overwrite conn->in in call_delayed(), then we need a different way 
> to find the original conn->in. I couldn't find a nice way and decided to 
> settle with the duplication.

Ah, okay, understood. Even in case we'd be able to restore conn->in it
would be the same amount of code again, but harder to follow.


Juergen

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  reply	other threads:[~2021-06-24  9:20 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16 14:43 [PATCH 00/10] tools/xenstored: Bug fixes + Improve Live-Update Julien Grall
2021-06-16 14:43 ` [PATCH 01/10] MAINTAINERS: Add myself as reviewers for tools/xenstore Julien Grall
2021-06-16 15:15   ` Juergen Gross
2021-06-16 14:43 ` [PATCH 02/10] tools/xenstored: Introduce lu_get_connection() and use it Julien Grall
2021-06-21  8:21   ` Luca Fancellu
2021-06-24  7:21   ` Juergen Gross
2021-06-16 14:43 ` [PATCH 03/10] tools/xenstore: Don't assume conn->in points to the LU request Julien Grall
2021-06-21  8:55   ` Luca Fancellu
2021-06-24  8:06     ` Julien Grall
2021-06-24  7:32   ` Juergen Gross
2021-06-24  7:34     ` Juergen Gross
2021-06-24  7:56       ` Luca Fancellu
2021-06-24  8:05         ` Juergen Gross
2021-06-16 14:43 ` [PATCH 04/10] tools/xenstored: Limit the number of requests a connection can delay Julien Grall
2021-06-21  9:02   ` Luca Fancellu
2021-06-24  7:35   ` Juergen Gross
2021-06-16 14:43 ` [PATCH 05/10] tools/xenstored: xenstored_core.h should include fcntl.h Julien Grall
2021-06-21  9:03   ` Luca Fancellu
2021-06-24  7:36   ` Juergen Gross
2021-06-16 14:43 ` [PATCH 06/10] tools/xenstored: Introduce a wrapper for conn->funcs->can_{read, write} Julien Grall
2021-06-21  9:10   ` Luca Fancellu
2021-06-24  7:39   ` Juergen Gross
2021-06-16 14:43 ` [PATCH 07/10] tools/xenstored: delay_request: don't assume conn->in == in Julien Grall
2021-06-21  9:12   ` Luca Fancellu
2021-06-24  7:44   ` Juergen Gross
2021-06-24  7:58     ` Julien Grall
2021-06-16 14:43 ` [PATCH 08/10] tools/xenstored: Extend restore code to handle multiple input buffer Julien Grall
2021-06-21  9:21   ` Luca Fancellu
2021-06-24  8:30   ` Juergen Gross
2021-06-24  8:42     ` Julien Grall
2021-06-24  9:20       ` Juergen Gross [this message]
2021-06-16 14:43 ` [PATCH 09/10] tools/xenstored: Dump delayed requests Julien Grall
2021-06-21  9:27   ` Luca Fancellu
2021-06-24  8:41   ` Juergen Gross
2021-06-24 10:28     ` Julien Grall
2021-06-24 10:45       ` Juergen Gross
2021-06-24 10:46         ` Julien Grall
2021-06-24 11:02           ` Juergen Gross
2021-06-24 11:17             ` Julien Grall
2021-06-16 14:43 ` [PATCH 10/10] tools/xenstored: Delay new transaction while Live-Update is pending Julien Grall
2021-06-21  9:30   ` Luca Fancellu
2021-06-24  9:23   ` Juergen Gross
2021-06-24 10:43 ` [PATCH 00/10] tools/xenstored: Bug fixes + Improve Live-Update Julien Grall

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