[libcamera-devel] [PATCH 1/4] libcamera: file: Add read/write support

[Laurent Pinchart]

Hi Niklas, Kieran,

On Mon, Jul 13, 2020 at 09:31:42AM +0100, Kieran Bingham wrote:
> Hi Niklas / Laurent,
> 
> On 13/07/2020 07:53, Niklas Söderlund wrote:
> > Hi Laurent,
> > 
> > Thanks for your work.
> > 
> > On 2020-07-12 17:44:16 +0300, Laurent Pinchart wrote:
> >> Add basic support to read and write data from/to a file, along with
> >> retrieving and setting the current read/write position.
> >>
> >> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> >> ---
> >>  include/libcamera/internal/file.h |   7 ++
> >>  src/libcamera/file.cpp            | 111 +++++++++++++++++++++++++++++-
> >>  2 files changed, 116 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/include/libcamera/internal/file.h b/include/libcamera/internal/file.h
> >> index e3e72132e336..ead94cdf29c9 100644
> >> --- a/include/libcamera/internal/file.h
> >> +++ b/include/libcamera/internal/file.h
> >> @@ -49,6 +49,12 @@ public:
> >>  	int error() const { return error_; }
> >>  	ssize_t size() const;
> >>  
> >> +	off_t pos() const { return pos_; }
> > 
> > Would it not be nicer to return lseek(fd_, 0, SEEK_CUR) here? That way 
> > we could avoid keeping pos_ in sync in potential corner cases.
> 
> Aha ... this would of course address my concerns about pos_ becoming
> invalid on error cases ...

Wouldn't it be more efficient to update pos_ in case of a read or write
error ? Efficiency may not be our primary concern here though. I don't
mind much either way, does anyone have a preference ?

> >> +	off_t seek(off_t pos);
> >> +
> >> +	ssize_t read(const Span<uint8_t> &data);
> >> +	ssize_t write(const Span<const uint8_t> &data);
> >> +
> >>  	Span<uint8_t> map(off_t offset = 0, ssize_t size = -1,
> >>  			  MapFlag flags = MapNoOption);
> >>  	bool unmap(uint8_t *addr);
> >> @@ -61,6 +67,7 @@ private:
> >>  	std::string name_;
> >>  	int fd_;
> >>  	OpenMode mode_;
> >> +	off_t pos_;
> >>  
> >>  	int error_;
> >>  	std::map<void *, size_t> maps_;
> >> diff --git a/src/libcamera/file.cpp b/src/libcamera/file.cpp
> >> index c471bde3fc68..8bd109090919 100644
> >> --- a/src/libcamera/file.cpp
> >> +++ b/src/libcamera/file.cpp
> >> @@ -73,7 +73,7 @@ LOG_DEFINE_CATEGORY(File);
> >>   * before performing I/O operations.
> >>   */
> >>  File::File(const std::string &name)
> >> -	: name_(name), fd_(-1), mode_(NotOpen), error_(0)
> >> +	: name_(name), fd_(-1), mode_(NotOpen), pos_(0), error_(0)
> >>  {
> >>  }
> >>  
> >> @@ -84,7 +84,7 @@ File::File(const std::string &name)
> >>   * setFileName().
> >>   */
> >>  File::File()
> >> -	: fd_(-1), mode_(NotOpen), error_(0)
> >> +	: fd_(-1), mode_(NotOpen), pos_(0), error_(0)
> >>  {
> >>  }
> >>  
> >> @@ -202,6 +202,7 @@ void File::close()
> >>  	::close(fd_);
> >>  	fd_ = -1;
> >>  	mode_ = NotOpen;
> >> +	pos_ = 0;
> >>  }
> >>  
> >>  /**
> >> @@ -237,6 +238,112 @@ ssize_t File::size() const
> >>  	return st.st_size;
> >>  }
> >>  
> >> +/**
> >> + * \fn off_t File::pos() const
> >> + * \brief Return current read or write position
> >> + *
> >> + * If the file is closed, this function returns 0.
> >> + *
> >> + * \return The current read or write position
> >> + */
> >> +
> >> +/**
> >> + * \brief Set the read or write position
> >> + * \param[in] pos The desired position
> >> + * \return The resulting offset from the beginning of the file on success, or a
> >> + * negative error code otherwise
> >> + */
> >> +off_t File::seek(off_t pos)
> >> +{
> >> +	if (!isOpen())
> >> +		return -EINVAL;
> >> +
> >> +	off_t ret = lseek(fd_, pos, SEEK_SET);
> >> +	if (ret < 0)
> >> +		return -errno;
> >> +
> >> +	pos_ = ret;
> >> +	return ret;
> >> +}
> >> +
> >> +/**
> >> + * \brief Read data from the file
> >> + * \param[in] data Memory to read data into
> >> + *
> >> + * Read at most \a data.size() bytes from the file into \a data.data(), and
> >> + * return the number of bytes read. If less data than requested is available,
> >> + * the returned byte count may be smaller than the requested size. If no more
> >> + * data is available, 0 is returned.
> >> + *
> >> + * The position of the file as returned by pos() is advanced by the number of
> >> + * bytes read. If an error occurs, the position isn't modified.
> >> + *
> >> + * \return The number of bytes read on success, or a negative error code
> >> + * otherwise
> >> + */
> >> +ssize_t File::read(const Span<uint8_t> &data)
> >> +{
> >> +	if (!isOpen())
> >> +		return -EINVAL;
> >> +
> >> +	size_t readBytes = 0;
> >> +	ssize_t ret = 0;
> >> +
> >> +	/* Retry in case of interrupted system calls. */
> >> +	while (readBytes < data.size()) {
> >> +		ret = ::read(fd_, data.data() + readBytes,
> >> +			     data.size() - readBytes);
> >> +		if (ret <= 0)
> >> +			break;
> >> +
> >> +		readBytes += ret;
> >> +	}
> >> +
> >> +	if (ret < 0 && !readBytes)
> >> +		return -errno;
> >> +
> >> +	pos_ += readBytes;
> >> +	return readBytes;
> >> +}
> >> +
> >> +/**
> >> + * \brief Write data to the file
> >> + * \param[in] data Memory containing data to be written
> >> + *
> >> + * Write at most \a data.size() bytes from \a data.data() to the file, and
> >> + * return the number of bytes written. If the file system doesn't have enough
> >> + * space for the data, the returned byte count may be less than requested.
> >> + *
> >> + * The position of the file as returned by pos() is advanced by the number of
> >> + * bytes written. If an error occurs, the position isn't modified.
> >> + *
> >> + * \return The number of bytes written on success, or a negative error code
> >> + * otherwise
> >> + */
> >> +ssize_t File::write(const Span<const uint8_t> &data)
> >> +{
> >> +	if (!isOpen())
> >> +		return -EINVAL;
> >> +
> >> +	size_t writtenBytes = 0;
> >> +
> >> +	/* Retry in case of interrupted system calls. */
> >> +	while (writtenBytes < data.size()) {
> >> +		ssize_t ret = ::write(fd_, data.data() + writtenBytes,
> >> +				      data.size() - writtenBytes);
> >> +		if (ret <= 0)
> >> +			break;
> >> +
> >> +		writtenBytes += ret;
> >> +	}
> >> +
> >> +	if (data.size() && !writtenBytes)
> >> +		return -errno;
> >> +
> >> +	pos_ += writtenBytes;
> >> +	return writtenBytes;
> >> +}
> >> +
> >>  /**
> >>   * \brief Map a region of the file in the process memory
> >>   * \param[in] offset The region offset within the file

-- 
Regards,

Laurent Pinchart