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_error structure 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_move() is similar to sd_bus_error_copy(), but will move any error information from e into dst, resetting the former. This function cannot fail, as no new memory is allocated. Note that if e is not set (or NULL) dst is initializated to SD_BUS_ERROR_NULL. Moreover, if dst is NULL no operation is executed on it and and resources held by e are freed and reset. 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_has_names_sentinel() is similar to sd_bus_error_has_name(), but takes multiple names to check against. The list must be terminated with NULL. sd_bus_error_has_names() is a macro wrapper around sd_bus_error_has_names_sentinel() that adds the NULL sentinel automatically.

sd_bus_error_free() will destroy resources held by e. The parameter itself will not be deallocated, and must be free(3)d 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() and sd_bus_error_move() return 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(), sd_bus_error_has_names(), and sd_bus_error_has_names_sentinel() return a non-zero value when e is non-NULL and the name field is equal to one of the given names, 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().

Notes¶

These APIs are implemented 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)