Re: [PATCH v2 2/2] tools/xenstore: simplify xenstored main loop

[Julien Grall <julien@xen.org>]

Hi Juergen,

On 17/05/2021 07:10, Juergen Gross wrote:
> On 14.05.21 19:05, Julien Grall wrote:
>> Hi Juergen,
>>
>> On 14/05/2021 12:56, Juergen Gross wrote:
>>> The main loop of xenstored is rather complicated due to different
>>> handling of socket and ring-page interfaces. Unify that handling by
>>> introducing interface type specific functions can_read() and
>>> can_write().
>>>
>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>> ---
>>> V2:
>>> - split off function vector introduction (Julien Grall)
>>> ---
>>>   tools/xenstore/xenstored_core.c   | 77 +++++++++++++++----------------
>>>   tools/xenstore/xenstored_core.h   |  2 +
>>>   tools/xenstore/xenstored_domain.c |  2 +
>>>   3 files changed, 41 insertions(+), 40 deletions(-)
>>>
>>> diff --git a/tools/xenstore/xenstored_core.c 
>>> b/tools/xenstore/xenstored_core.c
>>> index 856f518075..883a1a582a 100644
>>> --- a/tools/xenstore/xenstored_core.c
>>> +++ b/tools/xenstore/xenstored_core.c
>>> @@ -1659,9 +1659,34 @@ static int readfd(struct connection *conn, 
>>> void *data, unsigned int len)
>>>       return rc;
>>>   }
>>> +static bool socket_can_process(struct connection *conn, int mask)
>>> +{
>>> +    if (conn->pollfd_idx == -1)
>>> +        return false;
>>> +
>>> +    if (fds[conn->pollfd_idx].revents & ~(POLLIN | POLLOUT)) {
>>> +        talloc_free(conn);
>>> +        return false;
>>> +    }
>>> +
>>> +    return (fds[conn->pollfd_idx].revents & mask) && !conn->is_ignored;
>>> +}
>>> +
>>> +static bool socket_can_write(struct connection *conn)
>>> +{
>>> +    return socket_can_process(conn, POLLOUT);
>>> +}
>>> +
>>> +static bool socket_can_read(struct connection *conn)
>>> +{
>>> +    return socket_can_process(conn, POLLIN);
>>> +}
>>> +
>>>   const struct interface_funcs socket_funcs = {
>>>       .write = writefd,
>>>       .read = readfd,
>>> +    .can_write = socket_can_write,
>>> +    .can_read = socket_can_read,
>>>   };
>>>   static void accept_connection(int sock)
>>> @@ -2296,47 +2321,19 @@ int main(int argc, char *argv[])
>>>               if (&next->list != &connections)
>>>                   talloc_increase_ref_count(next);
>>> -            if (conn->domain) {
>>> -                if (domain_can_read(conn))
>>> -                    handle_input(conn);
>>> -                if (talloc_free(conn) == 0)
>>> -                    continue;
>>> -
>>> -                talloc_increase_ref_count(conn);
>>> -                if (domain_can_write(conn) &&
>>> -                    !list_empty(&conn->out_list))
>>
>> AFAICT, the check "!list_empty(&conn->out_list)" can be safely removed 
>> because write_messages() will check if the list is empty (list_top() 
>> returns NULL in this case). Is that correct?
> 
> Yes.

Thanks, how about adding in the commit message:

"Take the opportunity to remove the empty list check before calling 
write_messages() because the function is already able to cope with an 
empty list."

I can update the commit message while committing it.

Cheers,

-- 
Julien Grall