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

sd_device_ref(), sd_device_unref(), and sd_device_unrefp() were added in version 251.

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

1. Clean-up Variable Attribute https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html systemd 257.7 SD_DEVICE_REF(3)

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

#include<systemd/sd-device.h>sd_device*sd_device_ref(sd_device*device);sd_device*sd_device_unref(sd_device*device);voidsd_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-upVariableAttribute[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.