sd_hwdb_get(3) — Linux manual page


SD_HWDB_GET(3)                 sd_hwdb_get                SD_HWDB_GET(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       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

       Returned errors may indicate the following problems:

           A parameter is NULL.

           Added in version 246.

           An entry for the specified modalias was not found.

           Added in version 246.

           sd_hwdb_seek() was not called before sd_hwdb_enumerate().

           Added in version 246.

NOTES         top

       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

EXAMPLES         top

       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);

             return 0;

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

       The effect is similar to calling systemd-hwdb query

HISTORY         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
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       (which is not part of the original manual page), send a mail to

systemd 257~devel                                         SD_HWDB_GET(3)

Pages that refer to this page: sd-hwdb(3)sd_hwdb_new(3)systemd.directives(7)systemd.index(7)