NAME

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

SYNOPSIS

       #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);

DESCRIPTION

       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.

RETURN VALUE

       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.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           A parameter is NULL.

       -ENOENT
           An entry for the specified modalias was not found.

       -EAGAIN
           sd_hwdb_seek() was not called before sd_hwdb_enumerate().

NOTES

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

EXAMPLES

       Example 1. Look up hwdb entries for a USB device

           /* SPDX-License-Identifier: CC0-1.0 */

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

           int print_usb_properties(uint16_t vid, uint16_t pid) {
             char match[STRLEN("usb:vp") + DECIMAL_STR_MAX(uint16_t) * 2];
             sd_hwdb *hwdb;
             const char *key, *value;
             int r;

             /* Match this USB vendor and product ID combination */
             xsprintf(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.

SEE ALSO

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