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.

           Added in version 246.

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

           Added in version 246.

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

           Added in version 246.

NOTES

       Functions described here are available as a shared library, which can be compiled against
       and linked to with the libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be not multi-thread-safe.
       This means that the code calling the functions described here must not call setenv(3) from
       a parallel thread. It is recommended to only do calls to setenv() from an early phase of
       the program when no other threads have been started.

EXAMPLES

       Example 1. Look up hwdb entries for a USB device

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

           #define _GNU_SOURCE 1
           #include <stdio.h>
           #include <stdint.h>
           #include <systemd/sd-hwdb.h>

           int print_usb_properties(uint16_t vid, uint16_t pid) {
             char match[128];
             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.

HISTORY

       sd_hwdb_get(), sd_hwdb_seek(), sd_hwdb_enumerate(), and SD_HWDB_FOREACH_PROPERTY() were
       added in version 246.

SEE ALSO

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