sd_hwdb_get

systemd
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

## 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()`.

## Examples

Look up hwdb entries for a USB device

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