Re: [Qemu-devel] Re: [RFC][PATCH v5 01/21] Move code related to fd handlers into utility functions

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On 12/07/2010 07:31 AM, Jes Sorensen wrote:
> On 12/03/10 19:03, Michael Roth wrote:
>> This allows us to implement an i/o loop outside of vl.c that can
>> interact with objects that use qemu_set_fd_handler()
>>
>> Signed-off-by: Michael Roth<mdroth@linux.vnet.ibm.com>
>
> This commit message really tells us nothing. Please be more specific
> about what is in the commit.
>

Currently, in qemu, the virtagent client/server functionality is driven 
by vl.c:main_loop_wait(), which implements a select() loop that kicks 
off handlers registered for various FDs/events via qemu_set_fd_handler().

To share the code with the agent, qemu-va.c, I re-implemented this i/o 
loop to do same thing, along with vl.c:qemu_set_fd_handler*() and 
friends. It was big nasty copy/paste job and I think most of the 
reviewers agreed that the i/o loop code should be shared.

This commit moves the shared code into back-end utility functions that 
get called by vl.c:qemu_set_fd_handler()/qemu_process_fd_handlers() and 
friends for qemu, and by 
qemu-tools.c:qemu_set_fd_handler()/qemu_process_fd_handlers() for tools.

So now to interact with code that uses qemu_set_fd_handler() you can 
built a select() loop around these utility functions.

>> diff --git a/qemu-ioh.c b/qemu-ioh.c
>> new file mode 100644
>> index 0000000..cc71470
>> --- /dev/null
>> +++ b/qemu-ioh.c
>> @@ -0,0 +1,115 @@
>> +/*
>> + * QEMU System Emulator
>> + *
>> + * Copyright (c) 2003-2008 Fabrice Bellard
>> + *
>> + * Permission is hereby granted, free of charge, to any person obtaining a copy
>> + * of this software and associated documentation files (the "Software"), to deal
>> + * in the Software without restriction, including without limitation the rights
>> + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
>> + * copies of the Software, and to permit persons to whom the Software is
>> + * furnished to do so, subject to the following conditions:
>
> Is this moved or new code? If the former, fine, but if it is new code,
> you might want to leave your own name on the (c). I presume at least
> some of the changes are (c) 2010?
>

It's moved out from vl.c, nearly verbatim...

>> +/* XXX: fd_read_poll should be suppressed, but an API change is
>> +   necessary in the character devices to suppress fd_can_read(). */
>
> XXX in the comment isn't really of much use. Please make it more
> explicit, or put your name in if it is a statement you wish to make.
>

Even down to the comments :)

>> +int qemu_set_fd_handler3(void *ioh_record_list,
>> +                         int fd,
>> +                         IOCanReadHandler *fd_read_poll,
>> +                         IOHandler *fd_read,
>> +                         IOHandler *fd_write,
>> +                         void *opaque)
>
> I am not happy with this addition of numbers to these functions, it
> doesn't tell us why we have a 3 and how it differs from 2. If 3 is
> really the backend for implementing 2, maybe it would be better to name
> it __qemu_set_fd_handler2() and then have macros/wrappers calling into it.
>

That was the initial plan, but qemu_set_fd_handler2() is a back-end of 
sorts for qemu_set_fd_handler(), so I was just trying to be consistent 
with the naming. Personally I don't have any objections one way or the 
other.

> Cheers,
> Jes
>