x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_DEVICE_REF(3) sd_device_ref SD_DEVICE_REF(3)
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
systemd 254 SD_DEVICE_REF(3)
Want to link to this manual page? Use this URL:
<http://star2.abcm.com/cgi-bin/bsdi-man?query=sd_device_ref&sektion=3&manpath=>