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_move, sd_bus_error_is_set, sd_bus_error_has_name, sd_bus_error_has_names_sentinel, sd_bus_error_has_names — 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_move( | sd_bus_error *dst, |
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); |
int sd_bus_error_has_names_sentinel( | const sd_bus_error *e, |
...); |
#define sd_bus_error_has_names(e, ...) sd_bus_error_has_names_sentinel(e, ..., NULL)
The sd_bus_error structure carries information about a D-Bus error condition, or lack thereof. 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, and signifies lack of an error, i.e. success. Assign
SD_BUS_ERROR_NULL to the structure in order to initialize 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
contents again when they are not required anymore (see above). Do not use this call on error structures
that have already been set. If you intend to reuse an error structure, free the old data stored in it
with sd_bus_error_free() first.
sd_bus_error_set() will return an errno-like value (see
errno(3))
determined from the specified error name name. If name is
NULL, it is assumed that no error occurred, and 0 is returned.
If name is nonnull, a negative value is always returned. If
e is NULL, no error structure is initialized, but
name is still converted into an errno-style value.
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).
sd_bus_error_set() is designed to 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 will be set instead and
-ENOMEM returned.
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() may, 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 immediately return 0 if the
specified error parameter error is 0. Otherwise, it 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 and the absolute value is
used implicitly. If the specified error error is non-zero, 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 e has been set with an error value before.
Otherwise, it will return immediately. If the strings in e were set using
sd_bus_error_set_const(), they will be shared. Otherwise, they will be
copied. Before this call, dst must be unset, i.e. either freshly initialized with
NULL or reset using sd_bus_error_free().
sd_bus_error_copy() generally returns 0 or a negative
errno-like value based on the input parameter e:
0 if it was unset and a negative integer if it was set to some error, similarly to
sd_bus_error_set(). It may however also return an error generated internally, for
example -ENOMEM if a memory allocation fails.
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, dst is initialized to
SD_BUS_ERROR_NULL. Moreover, if dst is
NULL no operation is executed on it and resources held by e
are freed and reset. Returns a converted errno-like, non-positive error value.
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.
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().
The functions sd_bus_error_set(), sd_bus_error_setf(),
and sd_bus_error_set_const() always return 0 when the specified
error value is NULL, and a negative errno-like value corresponding to the
name parameter otherwise. The functions
sd_bus_error_set_errno(), sd_bus_error_set_errnof() and
sd_bus_error_set_errnofv(), return 0 when the specified error
value is 0, and a negative errno-like value corresponding to the
error parameter otherwise. If an error occurs internally, one of the negative
error values listed below will be returned. This allows those functions to be conveniently used in a
return statement, see the example below.
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 a
negative error value converted from the source error, and zero if the error has not been set. This
allows those functions to be conveniently used in a return statement, see the
example below.
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.
Return value may indicate the following problems in the invocation of the function itself:
On success, 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_copy(), and sd_bus_error_move() will return a
negative converted errno-style value, or 0 if the error
parameter is NULL or unset. D-Bus errors are converted to the integral
errno-style value, and the mapping mechanism is extensible, see the discussion
above. This effectively means that almost any negative errno-style value can be
returned.
Example 1. Using the negative return value to propagate an error
/* SPDX-License-Identifier: CC0-1.0 */
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sd-bus.h>
int writer_with_negative_errno_return(int fd, sd_bus_error *error) {
const char *message = "Hello, World!\n";
ssize_t n = write(fd, message, strlen(message));
if (n >= 0)
return n; /* On success, return the number of bytes written, possibly 0. */
/* On error, initialize the error structure, and also propagate the errno
* value that write(2) set for us. */
return sd_bus_error_set_errnof(error, errno, "Failed to write to fd %i: %m", fd);
}
These APIs are implemented as a shared
library, which can be compiled and linked to with the
libsystemd pkg-config(1)
file.