Description¶

The sd_device_enumerator family of functions provides a way to iterate over devices recognized by systemd-udevd(8). The enumerator allows filtering and matching devices by subsystem, properties and other attributes.

sd_device_enumerator_new() creates a new device enumerator object and stores the result in the pointer referenced by ret. Returns 0 on success, or a negative errno-style error code on failure.

sd_device_enumerator_ref() increases the reference count of the specified enumerator by one.

sd_device_enumerator_unref() decreases the reference count of the enumerator by one. When the reference count reaches zero, the enumerator object is destroyed and cannot be used anymore, so further calls to sd_device_enumerator_unref() or sd_device_enumerator_unrefp() are illegal.

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

{
  __attribute__((cleanup(sd_device_enumerator_unrefp))) sd_device_enumerator *enumerator = NULL;
  int r;
  …
  r = sd_device_enumerator_new(&enumerator);
  if (r < 0)
    fprintf(stderr, "Failed to allocate sd_device_enumerator: %s\n", strerror(-r));
  …
}

sd_device_enumerator_ref() and sd_device_enumerator_unref() execute no operation if the enumerator is NULL. sd_device_enumerator_unrefp() will first dereference its argument, which must not be NULL, and will execute no operation if that is NULL.

Return Value¶

sd_device_enumerator_new() returns 0 on success or a negative errno-style error code on failure.

sd_device_enumerator_ref() always returns the enumerator pointer.

sd_device_enumerator_unref() always returns NULL.

Example¶

/* SPDX-License-Identifier: MIT-0 */

#include <stdio.h>
#include <systemd/sd-device.h>

int main(void) {
    sd_device_enumerator *enumerator;
    int r;

    r = sd_device_enumerator_new(&enumerator);
    if (r < 0) {
        fprintf(stderr, "Failed to create enumerator: %s\n", strerror(-r));
        return 1;
    }

    sd_device_enumerator_ref(enumerator);
    sd_device_enumerator_unref(enumerator);

    sd_device_enumerator_unref(enumerator);

    return 0;
}

History¶

sd_device_enumerator_new(), sd_device_enumerator_ref(), sd_device_enumerator_unref(), and sd_device_enumerator_unrefp() were added in version 240.

See Also¶

sd_device_ref(3), sd_device_enumerator_add_match_parent(3)