[libcamera-devel] [PATCH 2/5] libcamera: media_device: Add function to get a MediaLink

[Laurent Pinchart]

Hello,

On Monday, 7 January 2019 10:57:30 EET Jacopo Mondi wrote:
> On Fri, Jan 04, 2019 at 05:33:16PM +0100, Niklas Söderlund wrote:
> > On 2019-01-03 18:38:56 +0100, Jacopo Mondi wrote:
> > > Add three overloaded functions 'link()' to retrieve a link between two
> > > pads. Each overloaded implementation exposes a different method to
> > > identify the source and sink entities.
> > > 
> > > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > > ---
> > > 
> > >  src/libcamera/include/media_device.h |   6 ++
> > >  src/libcamera/media_device.cpp       | 119 +++++++++++++++++++++++++++
> > >  2 files changed, 125 insertions(+)

[snip]

> > > diff --git a/src/libcamera/media_device.cpp
> > > b/src/libcamera/media_device.cpp index 2f9490c..6892300 100644
> > > --- a/src/libcamera/media_device.cpp
> > > +++ b/src/libcamera/media_device.cpp
> > > @@ -306,6 +306,125 @@ MediaEntity *MediaDevice::getEntityByName(const
> > > std::string &name) const
> > >  	return nullptr;
> > >  }
> > > 
> > > +/**
> > > + * \brief Return the MediaLink that connects two entities identified by
> > > name

s/Return/Retrieve/

The link doesn't actually connect the two entities directly, it connects two 
pads. I'd write this as

"Retrieve the MediaLink connecting two pads, identified by entity name and pad 
index."

> > > + * \param sourceName The source entity name
> > > + * \param sourceIdx The index of the source pad
> > > + * \param sinkName The sink entity name
> > > + * \param sinkIdx The index of the sink pad
> > > + *
> > > + * Find link that connects the pads at index \a sourceIdx of the source

s/Find/Find the/

> > > + * entity with name \a sourceName, to the pad at index \a sinkIdx of
> > > the
> > > + * sink entity with name \a sinkName, if any.
> > > + *
> > > + * \sa MediaDevice::link(const MediaEntity *source, unsigned int
> > > sourceIdx, const MediaEntity *sink, unsigned int sinkIdx) const + * \sa
> > > MediaDevice::link(const MediaPad *source, const MediaPad *sink) const +
> > > *
> > > + * \return The link that connects the two entities, nullptr otherwise

", or nullptr if no such link exists"

> > > + */
> > > +MediaLink *MediaDevice::link(const std::string sourceName, unsigned int
> > > sourceIdx,
> > > +			     const std::string sinkName, unsigned int sinkIdx)
> > > const

Isn't it dangerous to create a function that allows modifying a link from a 
const MediaDevice ? Should you provide both

	MediaLink *MediaDevice::link(...)
	const MediaLink *MediaDevice::link(...) const

? If you don't want to provide both I think you could go for the former only, 
as I don't think we'll have to deal with const MediaDevice pointers.

> > > +{
> > > +	const MediaEntity *source = getEntityByName(sourceName);
> > > +	if (!source) {
> > > +		LOG(Error) << "Failed to find entity with name: "
> > > +			   << sourceName << "\n";

I'd go for LOG(Debug) at most. I think it's a valid use case for a user to 
call this function to get a link without knowing whether it is present in the 
graph. This can be used to test for the availability of a link in a media 
device that supports multiple configurations. Even as a debug message I'm not 
sure how valuable this is. Same for the messages below.

All these comments apply to the other two functions below.

> > > +		return nullptr;
> > > +	}
> > > +
> > > +	const MediaPad *sourcePad = source->getPadByIndex(sourceIdx);
> > > +	if (!sourcePad) {
> > > +		LOG(Error) << "Entity \"" << sourceName << "\" "
> > > +			   << "has no pad at index " << sourceIdx << "\n";
> > > +		return nullptr;
> > > +	}
> > > +
> > > +	const MediaEntity *sink = getEntityByName(sinkName);
> > > +	if (!sink) {
> > > +		LOG(Error) << "Failed to find entity with name: "
> > > +			   << sinkName << "\n";
> > > +		return nullptr;
> > > +	}
> > > +
> > > +	const MediaPad *sinkPad = sink->getPadByIndex(sinkIdx);
> > > +	if (!sinkPad) {
> > > +		LOG(Error) << "Entity \"" << sinkName << "\" "
> > > +			   << "has no pad at index " << sinkIdx << "\n";
> > > +		return nullptr;
> > > +	}
> > > +
> > > +	return link(sourcePad, sinkPad);
> > 
> > How about just resolving the source and sink MediaEntity's here and then
> > 
> >     return link(source, sourceIdx, sink, sinkIdx);
> > 
> > This would reduce the code duplication.
> 
> Ah, right, no need to search for the source and sink pads here.
> I'll fix.
> 
> > > +}
> > > +
> > > +/**
> > > + * \brief Return the MediaLink that connects two entities
> > > + * \param source The source entity
> > > + * \param sourceIdx The index of the source pad
> > > + * \param sink The sink entity
> > > + * \param sinkIdx The index of the sink pad
> > > + *
> > > + * Find link that connects the pads at index \a sourceIdx of the source
> > > + * entity \a source, to the pad at index \a sinkIdx of the sink entity
> > > \a
> > > + * sink, if any.
> > > + *
> > > + * \sa MediaDevice::link(const std::string sourceName, unsigned int
> > > sourceIdx, const std::string sinkName, unsigned int sinkIdx) const + *
> > > \sa MediaDevice::link(const MediaPad *source, const MediaPad *sink)
> > > const + *
> > > + * \return The link that connects the two entities, nullptr otherwise
> > > + */
> > > +MediaLink *MediaDevice::link(const MediaEntity *source, unsigned int
> > > sourceIdx,
> > > +			     const MediaEntity *sink, unsigned int sinkIdx)
> > > const
> > > +{
> > > +
> > > +	const MediaPad *sourcePad = source->getPadByIndex(sourceIdx);
> > > +	if (!sourcePad) {
> > > +		LOG(Error) << "Entity \"" << source->name() << "\" "
> > > +			   << "has no pad at index " << sourceIdx << "\n";
> > > +		return nullptr;
> > > +	}
> > > +
> > > +	const MediaPad *sinkPad = sink->getPadByIndex(sinkIdx);
> > > +	if (!sinkPad) {
> > > +		LOG(Error) << "Entity \"" << sink->name() << "\" "
> > > +			   << "has no pad at index " << sinkIdx << "\n";
> > > +		return nullptr;
> > > +	}
> > > +
> > > +	return link(sourcePad, sinkPad);
> > > +}
> > > +
> > > +/**
> > > + * \brief Return the MediaLink that connects two pads
> > > + * \param source The source pad
> > > + * \param sink The sink pad
> > > + *
> > > + * \sa MediaDevice::link(const std::string sourceName, unsigned int
> > > sourceIdx, const std::string sinkName, unsigned int sinkIdx) const + *
> > > \sa MediaDevice::link(const MediaEntity *source, unsigned int
> > > sourceIdx, const MediaEntity *sink, unsigned int sinkIdx) const
> > > + *
> > > + * \return The link that connects the two pads, nullptr otherwise
> > > + */
> > > +MediaLink *MediaDevice::link(const MediaPad *source, const MediaPad
> > > *sink) const
> > > +{
> > > +	if (!source || !sink)
> > > +		return nullptr;

Can this happen ?

> > > +	/*
> > > +	 * Now that we have made sure all instances are valid, compare
> > > +	 * their ids to find a matching link.
> > > +	 */
> > 
> > I like comments in the code it self. I don't like (but I still write
> > them my self) comments that are written in this tens, how about.
> > 
> >     Compare pad ids to find the link which connects the source and sink
> >     pads.
> 
> Ack for this and for the comments style in general.
> 
> > > +	for (MediaLink *link : source->links()) {
> > > +		if (link->sink()->id() != sink->id())
> > > +			continue;
> > > +
> > > +		if (link->sink()->entity()->id() != sink->entity()->id())
> > > +			continue;

Do you need this check given that the id is unique ? It seems to be only 
needed if you search based on pad index, not when searching on pad id. You 
could thus write

		if (link->sink()->id() == sink->id())
			return link;

> > > +		return link;
> > > +	}
> > > +
> > > +	return nullptr;
> > > +}
> > > +
> > >  /**
> > >   * \var MediaDevice::objects_
> > >   * \brief Global map of media objects (entities, pads, links) keyed by
> > >   their

-- 
Regards,

Laurent Pinchart