On 2/11/23 22:08, Laurent Pinchart wrote:
> The ftruncate() function is declared with the warn_unused_result
> attribute, which generates a warning when compiling libv4lconvert:
>
> [60/340] Compiling C object lib/libv4lconvert/libv4lconvert.so.0.0.0.p/control_libv4lcontrol.c.o
> ../lib/libv4lconvert/control/libv4lcontrol.c: In function ‘v4lcontrol_create’:
> ../lib/libv4lconvert/control/libv4lcontrol.c:728:17: warning: ignoring return value of ‘ftruncate’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
> 728 | ftruncate(shm_fd, V4LCONTROL_SHM_SIZE);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Fix it by checking the return value and falling back to malloc-ed memory
> for controls, as done when mmap() fails.
>
> While at it, fix a typo in a comment, and drop an unneeded "error" word
> from an error message.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Regards,
Hans
> ---
> lib/libv4lconvert/control/libv4lcontrol.c | 23 ++++++++++++++---------
> 1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/lib/libv4lconvert/control/libv4lcontrol.c b/lib/libv4lconvert/control/libv4lcontrol.c
> index 7296de1d0fcb..676719372bb7 100644
> --- a/lib/libv4lconvert/control/libv4lcontrol.c
> +++ b/lib/libv4lconvert/control/libv4lcontrol.c
> @@ -725,16 +725,21 @@ struct v4lcontrol_data *v4lcontrol_create(int fd, void *dev_ops_priv,
>
> if (shm_fd >= 0) {
> /* Set the shared memory size */
> - ftruncate(shm_fd, V4LCONTROL_SHM_SIZE);
> + int ret = ftruncate(shm_fd, V4LCONTROL_SHM_SIZE);
> + if (ret) {
> + perror("libv4lcontrol: shm ftruncate failed");
> + close(shm_fd);
> + } else {
> + /* Retrieve a pointer to the shm object */
> + data->shm_values = mmap(NULL, V4LCONTROL_SHM_SIZE,
> + PROT_READ | PROT_WRITE,
> + MAP_SHARED, shm_fd, 0);
> + close(shm_fd);
>
> - /* Retreive a pointer to the shm object */
> - data->shm_values = mmap(NULL, V4LCONTROL_SHM_SIZE, (PROT_READ | PROT_WRITE),
> - MAP_SHARED, shm_fd, 0);
> - close(shm_fd);
> -
> - if (data->shm_values == MAP_FAILED) {
> - perror("libv4lcontrol: error shm mmap failed");
> - data->shm_values = NULL;
> + if (data->shm_values == MAP_FAILED) {
> + perror("libv4lcontrol: shm mmap failed");
> + data->shm_values = NULL;
> + }
> }
> } else
> perror("libv4lcontrol: error creating shm segment failed");
