x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_BUS_ERROR(3) sd_bus_error SD_BUS_ERROR(3)
NAME
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
SYNOPSIS
#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)
DESCRIPTION
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.
o 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[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.
o 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.
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().
RETURN VALUE
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.
EXAMPLES
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: %m", fd);
}
NOTES
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.
SEE ALSO
systemd(1), sd-bus(3), sd-bus-errors(3), sd_bus_error_add_map(3),
errno(3), strerror_r(3)
NOTES
1. Valid Names
https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names
systemd 254 SD_BUS_ERROR(3)
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