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
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_set_error_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(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.
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.
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().
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systemd 233 SD_BUS_ERROR(3)