Hi Greg,
Yeah, I used a wrong term when was asking about "callback". Actually I need
asynchronous notification, so I can pend a task on some primitive like a
semaphore.
Thank you for replying with an example. I will examine it.
Best regards,
Petro
On Wed, Dec 1, 2021, 8:43 PM Gregory Nutt <spudan...@gmail.com> wrote:
>
> > I have a question regarding FS automount functionality. Is there a way
> > to get a callback when file system is mounted and ready to be
> > accessed? Or the only way is to implement a polling loop like:
> >
> > while ( access( "/mnt/sdcard0", F_OK ) != 0 )
> > {
> > sleep(1);
> > }
>
> No, there will never never be callbacks from the OS into application
> code. That is not the POSIX way. The POSIX way would use signals for
> things like this.
>
> Look in drivers/, there are many drivers that notify applications of
> events via signals. Try searching for "notify".
>
> Here is one of many examples that provides a signal when a button is
> pressed: drivers/input/button_upper.c. That notification interface is
> described in include/nuttx/buttons.h:
>
> 66 /* Command: BTNIOC_REGISTER
> 67 * Description: Register to receive a signal whenever there is
> a change in
> 68 * the state of button inputs. This feature, of
> course, depends
> 69 * upon interrupt GPIO support from the platform.
> 70 * Argument: A read-only pointer to an instance of struct
> btn_notify_s
> 71 * Return: Zero (OK) on success. Minus one will be
> returned on failure
> 72 * with the errno value set appropriately.
> 73 */
> 74
> 75 #define BTNIOC_REGISTER _BTNIOC(0x0003)
>
> A similar notification interface could be added to the
> fs/mount/fs_automounter logic to notify an application when a monitored
> volume is mounted or unmounted.
>
>
