Re: [RFC PATCH 1/2] Add libv4l2rds library (with changes proposed in RFC)

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 08/09/2012 02:14 PM, Hans Verkuil wrote:
> On Thu August 9 2012 13:58:07 Hans de Goede wrote:
>> Hi Konke,
>>
>> As Gregor already mentioned there is no need to define libv4l2rdssubdir in configure.ac ,
>> so please drop that.
>>
>> Other then that I've some minor remarks (comments inline), with all those
>> fixed, this one is could to go. So hopefully the next version can be added
>> to git master!
>>
>> On 08/07/2012 05:11 PM, Konke Radlow wrote:
>>> ---
>>>    Makefile.am                     |    3 +-
>>>    configure.ac                    |    7 +-
>>>    lib/include/libv4l2rds.h        |  228 ++++++++++
>>>    lib/libv4l2rds/Makefile.am      |   11 +
>>>    lib/libv4l2rds/libv4l2rds.c     |  953 +++++++++++++++++++++++++++++++++++++++
>>>    lib/libv4l2rds/libv4l2rds.pc.in |   11 +
>>>    6 files changed, 1211 insertions(+), 2 deletions(-)
>>>    create mode 100644 lib/include/libv4l2rds.h
>>>    create mode 100644 lib/libv4l2rds/Makefile.am
>>>    create mode 100644 lib/libv4l2rds/libv4l2rds.c
>>>    create mode 100644 lib/libv4l2rds/libv4l2rds.pc.in
>>>
>>
>> <snip>
>>
>>> diff --git a/lib/include/libv4l2rds.h b/lib/include/libv4l2rds.h
>>> new file mode 100644
>>> index 0000000..4aa8593
>>> --- /dev/null
>>> +++ b/lib/include/libv4l2rds.h
>>> @@ -0,0 +1,228 @@
>>> +/*
>>> + * Copyright 2012 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
>>> + * Author: Konke Radlow <koradlow@gmail.com>
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU Lesser General Public License as published by
>>> + * the Free Software Foundation; either version 2.1 of the License, or
>>> + * (at your option) any later version.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * You should have received a copy of the GNU General Public License
>>> + * along with this program; if not, write to the Free Software
>>> + * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335  USA
>>> + */
>>> +
>>> +#ifndef __LIBV4L2RDS
>>> +#define __LIBV4L2RDS
>>> +
>>> +#include <errno.h>
>>> +#include <stdio.h>
>>> +#include <stdlib.h>
>>> +#include <string.h>
>>> +#include <stdbool.h>
>>> +#include <unistd.h>
>>> +#include <stdint.h>
>>> +#include <time.h>
>>> +#include <sys/types.h>
>>> +#include <sys/mman.h>
>>> +#include <config.h>
>>
>> You should never include config.h in a public header, also
>> are all the headers really needed for the prototypes in this header?
>>
>> I don't think so! Please move all the unneeded ones to the libv4l2rds.c
>> file!
>>
>>> +
>>> +#include <linux/videodev2.h>
>>> +
>>> +#ifdef __cplusplus
>>> +extern "C" {
>>> +#endif /* __cplusplus */
>>> +
>>> +#if HAVE_VISIBILITY
>>> +#define LIBV4L_PUBLIC __attribute__ ((visibility("default")))
>>> +#else
>>> +#define LIBV4L_PUBLIC
>>> +#endif
>>> +
>>> +/* used to define the current version (version field) of the v4l2_rds struct */
>>> +#define V4L2_RDS_VERSION (1)
>>> +
>>
>> What is the purpose of this field? Once we've released a v4l-utils with this
>> library we are stuck to the API we've defined, having a version field & changing it,
>> won't stop us from breaking existing apps, so once we've an official release we
>> simply cannot make ABI breaking changes, which is why most of my review sofar
>> has concentrated on the API side :)
>>
>> I suggest dropping this define and the version field from the struct.
>
> I think it is useful, actually. The v4l2_rds struct is allocated by the v4l2_rds_create
> so at least in theory it is possible to extend the struct in the future without breaking
> existing apps, provided you have a version number to check.

I disagree, if it gets extended only, then existing apps will just work, if an apps gets
compiled against a newer version with the extension then it is safe to assume it will run
against that newer version. The only reason I can see a version define being useful is
to make a newer app compile with an older version of the librarry, but that only requires
a version define, not a version field in the struct.

Regards,

Hans