Re: [PATCH yavta 6/7] Support setting control from values stored in a file

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

On Wed, Feb 20, 2019 at 11:26:52PM +0200, Sakari Ailus wrote:
> On Wed, Feb 20, 2019 at 02:51:22PM +0200, Laurent Pinchart wrote:
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > ---
> >  yavta.c | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> > 
> > diff --git a/yavta.c b/yavta.c
> > index 1490878c6f7e..2d49131a4271 100644
> > --- a/yavta.c
> > +++ b/yavta.c
> > @@ -1334,6 +1334,31 @@ static int video_parse_control_array(const struct v4l2_query_ext_ctrl *query,
> >  	__u32 value;
> >  
> >  	for ( ; isspace(*val); ++val) { };
> > +
> > +	if (*val == '<') {
> > +		/* Read the control value from the given file. */
> > +		ssize_t size;
> > +		int fd;
> > +
> > +		val++;
> > +		fd = open(val, O_RDONLY);
> > +		if (fd < 0) {
> > +			printf("unable to open control file `%s'\n", val);
> > +			return -EINVAL;
> > +		}
> > +
> > +		size = read(fd, ctrl->ptr, ctrl->size);
> 
> Note that a read of count reads *up to* count number of bytes from the file
> descriptor. In other words, it's perfectly correct for it to read less than
> requested.
> 
> How about using fread(3) instead? Or changing this into a loop?

Do you expect this to cause issues in practice ? When does read() return
less data than requested for regular files ?

> > +		if (size != (ssize_t)ctrl->size) {
> > +			printf("error reading control file `%s' (%s)\n", val,
> > +			       strerror(errno));
> > +			close(fd);
> > +			return -EINVAL;
> > +		}
> > +
> > +		close(fd);
> > +		return 0;
> > +	}
> > +
> >  	if (*val++ != '{')
> >  		return -EINVAL;
> >  

-- 
Regards,

Laurent Pinchart