[FFmpeg-devel,v3,1/2] lavf: Add general API for IO buffer synchronization.

This commit adds a new set of functions to avio and url subsystems, which
allow users to invoke IO buffer synchronization with the underlying media.
The most obvious target for this extension if the filesystem streams. Invoking
IO synchronization allows user applications to ensure that all written content
has reached the filesystem on the media and can be observed by other processes.

The public API for this is avio_sync() function, which can be called on
AVIOContext. The internal, lower layer API is ffurl_sync(), which works
directly on the underlying URLContext. URLContext backends can add support for
this new API by setting the sync handler to the new url_sync member of
URLProtocol. When no handler is set then the sync operation is a no-op,
the result code is AVERROR(ENOSYS).
---
 libavformat/avio.c    |  7 +++++++
 libavformat/avio.h    | 20 ++++++++++++++++++++
 libavformat/aviobuf.c | 17 +++++++++++++++++
 libavformat/url.h     | 12 ++++++++++++
 4 files changed, 56 insertions(+)

Ping?

On December 10, 2018 3:05:54 PM Andrey Semashev <andrey.semashev@gmail.com> 
wrote:

> This commit adds a new set of functions to avio and url subsystems, which
> allow users to invoke IO buffer synchronization with the underlying media.
> The most obvious target for this extension if the filesystem streams. Invoking
> IO synchronization allows user applications to ensure that all written content
> has reached the filesystem on the media and can be observed by other processes.
>
> The public API for this is avio_sync() function, which can be called on
> AVIOContext. The internal, lower layer API is ffurl_sync(), which works
> directly on the underlying URLContext. URLContext backends can add support for
> this new API by setting the sync handler to the new url_sync member of
> URLProtocol. When no handler is set then the sync operation is a no-op,
> the result code is AVERROR(ENOSYS).
> ---
> libavformat/avio.c    |  7 +++++++
> libavformat/avio.h    | 20 ++++++++++++++++++++
> libavformat/aviobuf.c | 17 +++++++++++++++++
> libavformat/url.h     | 12 ++++++++++++
> 4 files changed, 56 insertions(+)
>
> diff --git a/libavformat/avio.c b/libavformat/avio.c
> index 663789ec02..5754a7c20d 100644
> --- a/libavformat/avio.c
> +++ b/libavformat/avio.c
> @@ -623,6 +623,13 @@ int64_t ffurl_size(URLContext *h)
>     return size;
> }
>
> +int ffurl_sync(URLContext *h)
> +{
> +    if (h->prot->url_sync)
> +        return h->prot->url_sync(h);
> +    return AVERROR(ENOSYS);
> +}
> +
> int ffurl_get_file_handle(URLContext *h)
> {
>     if (!h || !h->prot || !h->prot->url_get_file_handle)
> diff --git a/libavformat/avio.h b/libavformat/avio.h
> index 75912ce6be..9e2ef14e60 100644
> --- a/libavformat/avio.h
> +++ b/libavformat/avio.h
> @@ -349,6 +349,14 @@ typedef struct AVIOContext {
>      * Try to buffer at least this amount of data before flushing it
>      */
>     int min_packet_size;
> +
> +    /**
> +     * A callback for synchronizing buffers with the media state.
> +     *
> +     * @return 0 on success, AVERROR(ENOSYS) if the operation is not supported
> +     *         and ignored, or other AVERROR < 0 on error.
> +     */
> +    int (*sync)(void *opaque);
> } AVIOContext;
>
> /**
> @@ -586,6 +594,18 @@ int avio_printf(AVIOContext *s, const char *fmt, ...) 
> av_printf_format(2, 3);
>  */
> void avio_flush(AVIOContext *s);
>
> +/**
> + * Flush internal buffers and ensure the synchronized state of the
> + * resource associated with the context s. This call may be expensive.
> + * Not all resources support syncing, this operation is a no-op
> + * if sync is not supported or needed.
> + * This function can only be used if s was opened by avio_open().
> + *
> + * @return 0 on success, AVERROR(ENOSYS) if the operation is not supported
> + *         and ignored, or other AVERROR < 0 on error.
> + */
> +int avio_sync(AVIOContext *s);
> +
> /**
>  * Read size bytes from AVIOContext into buf.
>  * @return number of bytes read or AVERROR
> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
> index 5a33f82950..c1c9334719 100644
> --- a/libavformat/aviobuf.c
> +++ b/libavformat/aviobuf.c
> @@ -243,6 +243,14 @@ void avio_flush(AVIOContext *s)
>         avio_seek(s, seekback, SEEK_CUR);
> }
>
> +int avio_sync(AVIOContext *s)
> +{
> +    avio_flush(s);
> +    if (s->sync)
> +        return s->sync(s->opaque);
> +    return AVERROR(ENOSYS);
> +}
> +
> int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
> {
>     int64_t offset1;
> @@ -978,6 +986,12 @@ static int64_t io_read_seek(void *opaque, int 
> stream_index, int64_t timestamp, i
>     return internal->h->prot->url_read_seek(internal->h, stream_index, 
>     timestamp, flags);
> }
>
> +static int io_sync(void *opaque)
> +{
> +    AVIOInternal *internal = opaque;
> +    return ffurl_sync(internal->h);
> +}
> +
> int ffio_fdopen(AVIOContext **s, URLContext *h)
> {
>     AVIOInternal *internal = NULL;
> @@ -1026,6 +1040,9 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
>
>         if (h->prot->url_read_seek)
>             (*s)->seekable |= AVIO_SEEKABLE_TIME;
> +
> +        if (h->prot->url_sync)
> +            (*s)->sync = io_sync;
>     }
>     (*s)->short_seek_get = io_short_seek;
>     (*s)->av_class = &ff_avio_class;
> diff --git a/libavformat/url.h b/libavformat/url.h
> index 4750bfff82..5b8cd22e5a 100644
> --- a/libavformat/url.h
> +++ b/libavformat/url.h
> @@ -97,6 +97,7 @@ typedef struct URLProtocol {
>     int (*url_delete)(URLContext *h);
>     int (*url_move)(URLContext *h_src, URLContext *h_dst);
>     const char *default_whitelist;
> +    int (*url_sync)(URLContext *h);
> } URLProtocol;
>
> /**
> @@ -228,6 +229,17 @@ int64_t ffurl_seek(URLContext *h, int64_t pos, int 
> whence);
> int ffurl_closep(URLContext **h);
> int ffurl_close(URLContext *h);
>
> +/**
> + * Flush any buffered data and synchronize the resource accessed
> + * by the URLContext h. This call may be expensive.
> + * Not all types of resources support syncing, the call is a no-op
> + * if sync is not supported or needed.
> + *
> + * @return 0 on success, AVERROR(ENOSYS) if the operation is not supported
> + *         and ignored, or other AVERROR < 0 on error.
> + */
> +int ffurl_sync(URLContext *h);
> +
> /**
>  * Return the filesize of the resource accessed by h, AVERROR(ENOSYS)
>  * if the operation is not supported by h, or another negative value
> --
> 2.19.1

Andrey Semashev (2018-12-10):
> This commit adds a new set of functions to avio and url subsystems, which
> allow users to invoke IO buffer synchronization with the underlying media.
> The most obvious target for this extension if the filesystem streams. Invoking
> IO synchronization allows user applications to ensure that all written content
> has reached the filesystem on the media and can be observed by other processes.
> 
> The public API for this is avio_sync() function, which can be called on
> AVIOContext. The internal, lower layer API is ffurl_sync(), which works
> directly on the underlying URLContext. URLContext backends can add support for
> this new API by setting the sync handler to the new url_sync member of
> URLProtocol. When no handler is set then the sync operation is a no-op,
> the result code is AVERROR(ENOSYS).
> ---
>  libavformat/avio.c    |  7 +++++++
>  libavformat/avio.h    | 20 ++++++++++++++++++++
>  libavformat/aviobuf.c | 17 +++++++++++++++++
>  libavformat/url.h     | 12 ++++++++++++
>  4 files changed, 56 insertions(+)

I have no more objections to the patch as it is, thanks. But I have no
opinion in favor of it either; it is useful in principle, but I do not
know if it is worth the extra maintenance for a use case like this
project. I will leave the judgement to others.

Regards,

On Thu, Dec 20, 2018 at 11:00:32AM +0100, Nicolas George wrote:
> Andrey Semashev (2018-12-10):
> > This commit adds a new set of functions to avio and url subsystems, which
> > allow users to invoke IO buffer synchronization with the underlying media.
> > The most obvious target for this extension if the filesystem streams. Invoking
> > IO synchronization allows user applications to ensure that all written content
> > has reached the filesystem on the media and can be observed by other processes.
> > 
> > The public API for this is avio_sync() function, which can be called on
> > AVIOContext. The internal, lower layer API is ffurl_sync(), which works
> > directly on the underlying URLContext. URLContext backends can add support for
> > this new API by setting the sync handler to the new url_sync member of
> > URLProtocol. When no handler is set then the sync operation is a no-op,
> > the result code is AVERROR(ENOSYS).
> > ---
> >  libavformat/avio.c    |  7 +++++++
> >  libavformat/avio.h    | 20 ++++++++++++++++++++
> >  libavformat/aviobuf.c | 17 +++++++++++++++++
> >  libavformat/url.h     | 12 ++++++++++++
> >  4 files changed, 56 insertions(+)
> 
> I have no more objections to the patch as it is, thanks. But I have no
> opinion in favor of it either; it is useful in principle, but I do not
> know if it is worth the extra maintenance for a use case like this
> project. I will leave the judgement to others.

IMHO, it looks useful and extra maintaince needed seems not major

thx

[...]

On 12/21/18 2:48 AM, Michael Niedermayer wrote:
> On Thu, Dec 20, 2018 at 11:00:32AM +0100, Nicolas George wrote:
>> Andrey Semashev (2018-12-10):
>>> This commit adds a new set of functions to avio and url subsystems, which
>>> allow users to invoke IO buffer synchronization with the underlying media.
>>> The most obvious target for this extension if the filesystem streams. Invoking
>>> IO synchronization allows user applications to ensure that all written content
>>> has reached the filesystem on the media and can be observed by other processes.
>>>
>>> The public API for this is avio_sync() function, which can be called on
>>> AVIOContext. The internal, lower layer API is ffurl_sync(), which works
>>> directly on the underlying URLContext. URLContext backends can add support for
>>> this new API by setting the sync handler to the new url_sync member of
>>> URLProtocol. When no handler is set then the sync operation is a no-op,
>>> the result code is AVERROR(ENOSYS).
>>> ---
>>>   libavformat/avio.c    |  7 +++++++
>>>   libavformat/avio.h    | 20 ++++++++++++++++++++
>>>   libavformat/aviobuf.c | 17 +++++++++++++++++
>>>   libavformat/url.h     | 12 ++++++++++++
>>>   4 files changed, 56 insertions(+)
>>
>> I have no more objections to the patch as it is, thanks. But I have no
>> opinion in favor of it either; it is useful in principle, but I do not
>> know if it is worth the extra maintenance for a use case like this
>> project. I will leave the judgement to others.
> 
> IMHO, it looks useful and extra maintaince needed seems not major

So, will this patchset be merged then?