> [...]
> >> >> +static int get_gpio_pin_state(struct irq_desc *irq_desc)
> >> >> +{
> >> >> + struct gpio_chip *gc = irq_data_get_irq_chip_data(&irq_desc->irq_data);
> >> >> +
> >> >> + return gc->get(gc, irq_desc->irq_data.hwirq);
> >> >> +}
> >> [...]
> >> >> + ssize_t status = get_gpio_pin_state(irq_desc);
> >> >
> >> >`get_gpio_pin_state()` returns an `int`, so I am not sure why `ssize_t` is used here.
> >> >
> >>
> >> I used `ssize_t` because I found gpiolib-sysfs.c uses `ssize_t`
> >>
> >> // drivers/gpio/gpiolib-sysfs.c
> >> static ssize_t value_show(struct device *dev,
> >> struct device_attribute *attr, char *buf)
> >> {
> >> struct gpiod_data *data = dev_get_drvdata(dev);
> >> struct gpio_desc *desc = data->desc;
> >> ssize_t status;
> >>
> >> mutex_lock(&data->mutex);
> >>
> >> status = gpiod_get_value_cansleep(desc);
> >> ...
> >> return status;
> >> }
> >>
> >> According to the book Advanced Programming in the UNIX Environment by
> >> W. Richard Stevens,
> >> With the 1990 POSIX.1 standard, the primitive system data type
> >> ssize_t was introduced to provide the signed return value...
> >>
> >> So ssize_t is fairly common, for example, the read and write syscall
> >> return a value of type ssize_t. But I haven't found out why ssize_t is
> >> better int.
> >> >
> >
> >Sorry if I wasn't clear, what prompted me to ask that question is the following:
> >`gc->get()` returns `int`, `get_gpio_pin_state()` returns `int`, yet you still
> >save the return value of `get_gpio_pin_state()` into a variable with type
> >`ssize_t` for no apparent reason. In the example you cited, `ssize_t` is used
> >because the show() callback of a sysfs attribute must return `ssize_t`, but here,
> >`interrupt_line_active()` returns `bool`, so I don't see any advantage over a
> >plain `int`. Anyways, I believe either one is fine, I just found it odd.
> >
> I don't understand why "the show() callback of a sysfs attribute
> must return `ssize_t`" instead of int. Do you think the rationale
> behind it is the same for this case? If yes, using "ssize_t" for
> status could be justified.
> [...]
Because it was decided that way, `ssize_t` is a better choice for that purpose
than plain `int`. You can see it in include/linux/device.h, that both the
show() and store() methods must return `ssize_t`.
What I'm arguing here, is that there is no reason to use `ssize_t` in this case.
Because `get_gpio_pin_state()` returns `int`. So when you do
```
ssize_t status = get_gpio_pin_state(...);
```
then the return value of `get_gpio_pin_state()` (which is an `int`), will be
converted to an `ssize_t`, and saved into `status`. I'm arguing that that is
unnecessary and a plain `int` would work perfectly well in this case. Anyways,
both work fine, I just found the unnecessary use of `ssize_t` here odd.
Regards,
Barnabás Pőcze
