[libcamera-devel] [PATCH 1/2] libcamera: Don't ignore the return value of read() and write()

[Kieran Bingham]

Hi Laurent,

On 29/04/2019 00:12, Laurent Pinchart wrote:
> The glibc read() and write() functions are defined with the
> __warn_unused_result__ attribute when using FORTIFY_SOURCE. Don't ignore
> their return value.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/libcamera/event_dispatcher_poll.cpp |  8 ++++++--
>  test/event.cpp                          | 13 +++++++++++--
>  2 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/src/libcamera/event_dispatcher_poll.cpp b/src/libcamera/event_dispatcher_poll.cpp
> index 1f0f352a8e0a..2621b7d96b1e 100644
> --- a/src/libcamera/event_dispatcher_poll.cpp
> +++ b/src/libcamera/event_dispatcher_poll.cpp
> @@ -162,7 +162,9 @@ void EventDispatcherPoll::processEvents()
>  void EventDispatcherPoll::interrupt()
>  {
>  	uint64_t value = 1;
> -	write(eventfd_, &value, sizeof(value));
> +	ssize_t ret = write(eventfd_, &value, sizeof(value));> +	if (ret < 0)

Do we care if ret != sizeof(value)? (I think it must be highly unlikely
that the read/write call doesn't at least read the 64 bit value...)

> +		LOG(Event, Error) << "Failed to interrupt event dispatcher";

What about printing the strerror(errno), as if this ever actually
happens (even if unlikely) it would be useful...

>  }
>  
>  short EventDispatcherPoll::EventNotifierSetPoll::events() const
> @@ -214,7 +216,9 @@ void EventDispatcherPoll::processInterrupt(const struct pollfd &pfd)
>  		return;
>  
>  	uint64_t value;
> -	read(eventfd_, &value, sizeof(value));
> +	ssize_t ret = read(eventfd_, &value, sizeof(value));
> +	if (ret < 0)
> +		LOG(Event, Error) << "Failed to process interrupt";


Same comments as above...

Could we ever expect ret == 0 on the read call (EOF?)? I presume as
we're checking with poll() in advance this should always have at least
one event to read.


I think the return values are probably fine, and the errno is optional
so with or without updates:


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>


>  }
>  
>  void EventDispatcherPoll::processNotifiers(const std::vector<struct pollfd> &pollfds)
> diff --git a/test/event.cpp b/test/event.cpp
> index 52bc0c7e77f5..9bd876153a18 100644
> --- a/test/event.cpp
> +++ b/test/event.cpp
> @@ -38,6 +38,7 @@ protected:
>  		EventDispatcher *dispatcher = CameraManager::instance()->eventDispatcher();
>  		std::string data("H2G2");
>  		Timer timeout;
> +		ssize_t ret;
>  
>  		EventNotifier readNotifier(pipefd_[0], EventNotifier::Read);
>  		readNotifier.activated.connect(this, &EventTest::readReady);
> @@ -46,7 +47,11 @@ protected:
>  		memset(data_, 0, sizeof(data_));
>  		size_ = 0;
>  
> -		write(pipefd_[1], data.data(), data.size());
> +		ret = write(pipefd_[1], data.data(), data.size());
> +		if (ret < 0) {
> +			cout << "Pipe write failed" << endl;
> +			return TestFail;
> +		}
>  
>  		timeout.start(100);
>  		dispatcher->processEvents();
> @@ -73,7 +78,11 @@ protected:
>  		notified_ = false;
>  		readNotifier.setEnabled(false);
>  
> -		write(pipefd_[1], data.data(), data.size());
> +		ret = write(pipefd_[1], data.data(), data.size());
> +		if (ret < 0) {
> +			cout << "Pipe write failed" << endl;
> +			return TestFail;
> +		}
>  
>  		timeout.start(100);
>  		dispatcher->processEvents();
> 

-- 
Regards
--
Kieran