SD_DEVICE_ENUMERATOR_NEW(3)

NAME
sd_device_enumerator_new, sd_device_enumerator_ref, sd_device_enumerator_unref, sd_device_enumerator_unrefp - Create, reference, and release a device enumerator object

SYNOPSIS

#include <systemd/sd-device.h>

int sd_device_enumerator_new(sd_device_enumerator **ret);

sd_device_enumerator* sd_device_enumerator_ref(sd_device_enumerator *enumerator);

sd_device_enumerator* sd_device_enumerator_unref(sd_device_enumerator *enumerator);

void sd_device_enumerator_unrefp(sd_device_enumerator **enumerator);

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[1]. 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.

  Errors

Returned errors may indicate the following problems:

-ENOMEM
    Memory allocation failed.

-EINVAL
    The argument is invalid.

EXAMPLE

Example 1. Using sd_device_enumerator_new()

    /* 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)

NOTES

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