Manpages - sd_hwdb_get.3

sd_hwdb_get, sd_hwdb_seek, sd_hwdb_enumerate, SD_HWDB_FOREACH_PROPERTY - Seek to a location in hwdb or access entries

  #include <systemd/sd-hwdb.h>

int sd_hwdb_get(sd_hwdb **/hwdb/, const char */modalias/, const char */key/, const char **/value/);*

int sd_hwdb_seek(sd_hwdb **/hwdb/, const char */modalias/);*

int sd_hwdb_enumerate(sd_hwdb **/hwdb/, const char **/key/, const char **/value/);*

SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value);

sd_hwdb_get() queries the hwdb object created earlier with sd_hwdb_new*(3) for entries matching the specified string modalias, and returns the value corresponding to the key key. The value is returned as a *NUL-terminated string in value. It must not be modified by the caller and is valid as long as a reference to hwdb is kept. When multiple patterns in the database match modalias, the one with the highest priority is used. See *hwdb*(7) for details.

sd_hwdb_seek() selects entries matching the specified string modalias. Subsequent queries with sd_hwdb_enumerate() will access the key-value pairs for that string.

sd_hwdb_enumerate() returns (in turn) all the key-value pairs defined for the string used with sd_hwdb_seek(). Each pair is returned as NUL-terminated strings in key and value. The strings must not be modified by the caller and are valid as long as a reference to hwdb is kept. When multiple patterns in the database match modalias, the combination of all matching key-value pairs is used. See *hwdb*(7) for details.

The SD_HWDB_FOREACH_PROPERTY() macro combines sd_hwdb_seek() and sd_hwdb_enumerate(). No error handling is performed and iteration simply stops on error. See the example below.

On success, sd_hwdb_get() and sd_hwdb_seek() return a non-negative integer. On failure, they return a negative errno-style error code.

sd_hwdb_enumerate() returns a positive integer if another key-value pair was found or zero if all entries have already been enumerated. On failure, it returns a negative errno-style error code.

These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd *pkg-config*(1) file.

Example 1. Look up hwdb entries for a USB device

    #include <stdio.h>
    #include <stdint.h>
    #include <sd-hwdb.h>

    int print_usb_properties(uint16_t vid, uint16_t pid) {
      char match[15];
      sd_hwdb *hwdb;
      const char *key, *value;
      int r;

      /* Match this USB vendor and product ID combination */
      snprintf(match, sizeof match, "usb:v%04Xp%04X", vid, pid);

      r = sd_hwdb_new(&hwdb);
      if (r < 0)
        return r;

      SD_HWDB_FOREACH_PROPERTY(hwdb, match, key, value)
        printf("%s: \"%s\" → \"%s\"\n", match, key, value);

      sd_hwdb_unref(hwdb);
      return 0;
    }

    int main(int argc, char **argv) {
      print_usb_properties(0x046D, 0xC534);
      return 0;
    }

The effect is similar to calling systemd-hwdb query usb:v046DpC534.

*systemd*(1), *systemd-udevd.service*(8), *sd-hwdb*(3), *systemd-hwdb*(8)