sd_bus_error(3) — Linux manual page


SD_BUS_ERROR(3)               sd_bus_error               SD_BUS_ERROR(3)

NAME         top

       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

SYNOPSIS         top

       #include <systemd/sd-bus.h>

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

       SD_BUS_ERROR_MAKE_CONST(name, message)


       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)

DESCRIPTION         top

       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

       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

       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

       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

RETURN VALUE         top

       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:

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

           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.

EXAMPLES         top

       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));

NOTES         top

       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

HISTORY         top

       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.

SEE ALSO         top

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

NOTES         top

        1. Valid D-Bus Names

COLOPHON         top

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       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
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       (which is not part of the original manual page), send a mail to

systemd 257~devel                                        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)