sd_bus_error

systemd
A monkey with a typewriter Zbigniew Jędrzejewski-Szmek zbyszek@in.waw.pl
sd_bus_error 3
sd_bus_error SD_BUS_ERROR_MAKE_CONST SD_BUS_ERROR_NULL sd_bus_error_free sd_bus_error_set sd_bus_error_setf sd_bus_error_set_const sd_bus_error_set_errno sd_bus_error_set_errnof sd_bus_error_set_errnofv sd_bus_error_get_errno sd_bus_error_copy sd_bus_error_is_set sd_bus_error_has_name sd-bus error handling

    #include <systemd/sd-bus.h>

    typedef struct {
            const char *name;
            const char *message;
            …
    } sd_bus_error;

`SD_BUS_ERROR_MAKE_CONST(name, message)`

`SD_BUS_ERROR_NULL`

void `sd_bus_error_free` sd_bus_error *e int `sd_bus_error_set` sd_bus_error *e const char *name const char *message int `sd_bus_error_setf` sd_bus_error *e const char *name const char *format … int `sd_bus_error_set_const` sd_bus_error *e const char *name const char *message int `sd_bus_error_set_errno` sd_bus_error *e int error int `sd_bus_error_set_errnof` sd_bus_error *e int error const char *format … int `sd_bus_error_set_errnofv` sd_bus_error *e int error const char *format va_list ap int `sd_bus_error_get_errno` const sd_bus_error *e int `sd_bus_error_copy` sd_bus_error *dst const sd_bus_error *e int `sd_bus_error_is_set` const sd_bus_error *e int `sd_bus_error_has_name` const sd_bus_error *e const char *name

## Description

The sd_bus_error structure carries information about a D-Bus error condition. The functions described below may be used to set and query fields in this structure. The name field contains a short identifier of an error. It should follow the rules for error names described in the D-Bus specification, subsection Valid Names. A number of common, standardized error names are described in sd-bus-errors 3, but additional domain-specific errors may be defined by applications. The message field usually contains a human-readable string describing the details, but might be NULL. An unset sd_bus_error structure should have both fields initialized to NULL. Set an error structure to `SD_BUS_ERROR_NULL` in order to reset both fields to NULL. When no longer necessary, resources held by the sd_bus_errorstructure should be destroyed with `sd_bus_error_free()`.

`sd_bus_error_set()` sets an error structure to the specified name and message strings. The strings will be copied into internal, newly allocated memory. It is essential to free the error structure again when it is not required anymore (see above). The function will return an `errno`-like negative value (see errno 3) determined from the specified error name. Various well-known D-Bus errors are converted to well-known `errno` counterparts, and the other ones to `-EIO`. See sd-bus-errors 3 for a list of well-known error names. Additional error mappings may be defined with sd_bus_error_add_map 3. If e is NULL, no error structure is initialized, but the error is still converted into an `errno`-style error. If name is `NULL`, it is assumed that no error occurred, and 0 is returned. This means that this function may be conveniently used in a `return` statement. If message is NULL, no message is set. This call can fail if no memory may be allocated for the name and message strings, in which case an `SD_BUS_ERROR_NO_MEMORY` error might be set instead and -ENOMEM be returned. Do not use this call on error structures that are already initialized. If you intend to reuse an error structure, free the old data stored in it with `sd_bus_error_free()` first.

`sd_bus_error_setf()` is similar to `sd_bus_error_set()`, but takes a printf 3 format string and corresponding arguments to generate the message field.

`sd_bus_error_set_const()` is similar to `sd_bus_error_set()`, but the string parameters are not copied internally, and must hence remain constant and valid for the lifetime of e. Use this call to avoid memory allocations when setting error structures. Since this call does not allocate memory, it will not fail with an out-of-memory condition as `sd_bus_error_set()` can, as described above. Alternatively, the `SD_BUS_ERROR_MAKE_CONST()` macro may be used to generate a literal, constant bus error structure on-the-fly.

`sd_bus_error_set_errno()` will set name from an `errno`-like value that is converted to a D-Bus error. strerror_r 3 will be used to set message. Well-known D-Bus error names will be used for name if applicable, otherwise a name in the `System.Error.` namespace will be generated. The sign of the specified error number is ignored. The absolute value is used implicitly. The call always returns a negative value, for convenient usage in `return` statements. This call might fail due to lack of memory, in which case an `SD_BUS_ERROR_NO_MEMORY` error is set instead, and -ENOMEM is returned.

`sd_bus_error_set_errnof()` is similar to `sd_bus_error_set_errno()`, but in addition to error, takes a printf 3 format string and corresponding arguments. The message field will be generated from format and the arguments.

`sd_bus_error_set_errnofv()` is similar to `sd_bus_error_set_errnof()`, but takes the format string parameters as va_arg 3 parameter list.

`sd_bus_error_get_errno()` converts the name field of an error structure to an `errno`-like (positive) value using the same rules as `sd_bus_error_set()`. If e is `NULL`, 0 will be returned.

`sd_bus_error_copy()` will initialize dst using the values in e. If the strings in e were set using `sd_bus_error_set_const()`, they will be shared. Otherwise, they will be copied. Returns a converted `errno`-like, negative error code.

`sd_bus_error_is_set()` will return a non-zero value if e is non-`NULL` and an error has been set, `false` otherwise.

`sd_bus_error_has_name()` will return a non-zero value if e is non-`NULL` and an error with the same name has been set, `false` otherwise.

`sd_bus_error_free()` will destroy resources held by e. The parameter itself will not be deallocated, and must be free 3d by the caller if necessary. The function may also be called safely on unset errors (error structures with both fields set to NULL), in which case it performs no operation. This call will reset the error structure after freeing the data, so that all fields are set to NULL. The structure may be reused afterwards.

## Return Value

The functions `sd_bus_error_set()`, `sd_bus_error_setf()`, and `sd_bus_error_set_const()`, when successful, return the negative errno value corresponding to the name parameter. The functions `sd_bus_error_set_errno()`, `sd_bus_error_set_errnof()` and `sd_bus_error_set_errnofv()`, when successful, return the negative value of the error parameter. If an error occurs, one of the negative error values listed below will be returned.

`sd_bus_error_get_errno()` returns `false` when e is `NULL`, and a positive errno value mapped from e->name otherwise.

`sd_bus_error_copy()` returns 0 or a positive integer on success, and a negative error value converted from the error name otherwise.

`sd_bus_error_is_set()` returns a non-zero value when e and the name field are non-`NULL`, zero otherwise.

`sd_bus_error_has_name()` returns a non-zero value when e is non-`NULL` and the name field is equal to name, zero otherwise.

## Reference ownership

sd_bus_error is not reference counted. Users should destroy resources held by it by calling `sd_bus_error_free()`. Usually, error structures are allocated on the stack or passed in as function parameters, but they may also be allocated dynamically, in which case it is the duty of the caller to free 3 the memory held by the structure itself after freeing its contents with `sd_bus_error_free()`.

## Errors

Returned errors may indicate the following problems:

`-EINVAL`

  Error was already set in sd_bus_error structure when one the error-setting functions was called.

`-ENOMEM`

  Memory allocation failed.

## Notes

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

## See Also

systemd 1, sd-bus 3, sd-bus-errors 3, sd_bus_error_add_map 3, errno 3, strerror_r 3