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NAME | SYNOPSIS | DESCRIPTION | REFERENCE OWNERSHIP | RETURN VALUE | EXAMPLES | NOTES | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SD_BUS_ERROR(3) sd_bus_error 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_setfv, 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_setfv(sd_bus_error *e, const char *name,
const char *format, va_list ap);
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 D-Bus Names[1]. 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() and sd_bus_error_setfv() are similar to
sd_bus_error_set(), but take a printf(3) format string and
corresponding arguments to generate the message field.
sd_bus_error_setf() uses variadic arguments, and
sd_bus_error_setfv() accepts the arguments as a va_arg(3)
parameter list.
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() and sd_bus_error_set_errnof() are
similar to sd_bus_error_set_errno(), but in addition to error,
take a printf(3) format string and corresponding arguments. The
message field will be generated from format and the arguments.
sd_bus_error_set_errnof() uses variadic arguments, and
sd_bus_error_set_errnofv() accepts the arguments as a 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.
Errors
Return value may indicate the following problems in the invocation
of the function itself:
-EINVAL
Error was already set in the sd_bus_error structure when one
the error-setting functions was called.
-ENOMEM
Memory allocation failed.
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: MIT-0 */
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <systemd/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: %s", fd, strerror(errno));
}
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
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(), and sd_bus_error_has_name() were added in
version 221.
sd_bus_error_move() was added in version 240.
sd_bus_error_has_names_sentinel() was added in version 247.
sd_bus_error_setfv() was added in version 252.
systemd(1), sd-bus(3), sd-bus-errors(3), sd_bus_error_add_map(3),
errno(3), strerror_r(3)
1. Valid D-Bus Names
https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_BUS_ERROR(3)
Pages that refer to this page: sd-bus(3), sd_bus_add_object(3), sd_bus_call(3), sd_bus_error_add_map(3), sd-bus-errors(3), sd_bus_message_new_method_error(3), sd_bus_reply_method_error(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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