SD_DEVICE_REF(3)

🌸 sd_device_ref(3), sd_device_unref(3), sd_device_unrefp(3) — the device ref-counting trio 🌸

okay bestie, this is the SD_DEVICE_REF(3) manual page, and we're talking about creating and destroying references to a device object. It's giving “I hold a tiny handle to a device and I refuse to leak it” energy. 💅✨

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✨ NAME ✨

sd_device_ref, sd_device_unref, sd_device_unrefp — create or destroy references to a device object. That's the whole vibe: ref it, unref it, or unrefp it with the cleanup-attribute magic. 🫶

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🦋 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);

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💅 DESCRIPTION 💅

sd_device_ref() increases the internal reference counter of device by one. One more little grip on the device, bestie. 🎀

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. Not “oopsie” illegal — like, actually illegal, so do not. 💀

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. So yes, the outer pointer has to actually exist; the inner one can be NULL and then it just chills. 🧚

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🔥 RETURN VALUE 🔥

sd_device_ref() always returns the argument, and sd_device_unref() always returns NULL. No surprises, bestie. ✨

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🌈 HISTORY 🌈

sd_device_ref(), sd_device_unref(), and sd_device_unrefp() were added in version 251. So they're not ancient relics; they're version 251 babies. 👑

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🎀 NOTES 🎀

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

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okay that's the whole page, bestie. The footer says source/version systemd 261.3 and the manual name SD_DEVICE_REF(3); there's no date printed on this footer, so I'm not inventing one. bye bestie, go unref responsibly 💖🫶✨