NAME

       sd_device_ref, sd_device_unref, sd_device_unrefp - Create or destroy references to a
       device object

SYNOPSIS

       #include <systemd/sd-device.h>

       sd_device* sd_device_ref(sd_device *device);

       sd_device* sd_device_unref(sd_device *device);

       void sd_device_unrefp(sd_device **device);

       sd_device_ref() increases the internal reference counter of device by one.

       sd_device_unref() decreases the internal reference counter of device by one. Once the
       reference count has dropped to zero, device is destroyed and cannot be used anymore, so
       further calls to sd_device_ref() or sd_device_unref() are illegal.

       sd_device_unrefp() is similar to sd_device_unref() but takes a pointer to a pointer to an
       sd_device object. This call is useful in conjunction with GCC's and LLVM's Clean-up
       Variable Attribute[1]. Note that this function is defined as an inline function. Use a
       declaration like the following, in order to allocate a device object that is freed
       automatically as the code block is left:

       {
         __attribute__((cleanup(sd_device_unrefp))) sd_device *device = NULL;
         int r;
         ...
         r = sd_device_new_from_syspath(&device, "...");
         if (r < 0) {
           errno = -r;
           fprintf(stderr, "Failed to allocate device: %m\n");
         }
         ...
       }

       sd_device_ref() and sd_device_unref() execute no operation if the argument is NULL.
       sd_device_unrefp() will first dereference its argument, which must not be NULL, and will
       execute no operation if that is NULL.

RETURN VALUE

       sd_device_ref() always returns the argument, and sd_device_unref() always returns NULL.

NOTES

        1. Clean-up Variable Attribute
           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html