system/systemd
system/systemd
1
0
Fork 0
mirror of https://github.com/systemd/systemd synced 2024-10-07 00:30:59 +00:00
Code Issues Packages Projects Releases Wiki Activity

man: split the description of sd_bus_error_set()

Browse source 
It was one giant all of text in pseudo-random order. Let's split it into
paragraphs talk about one subject each.

And unfortunately, the description of what happens when the error is not
set was not correct. In general, various functions treat 0/NULL as
not-an-error, and return 0.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2021-03-31 11:46:31 +02:00
parent b9c19bc384
commit af46237ea1
2 changed files with 93 additions and 106 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

197
man/sd_bus_error.xml
View file

@ -147,55 +147,54 @@
<refsect1>
<title>Description</title>
<para>The <structname>sd_bus_error</structname> 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
<structfield>name</structfield> field contains a short identifier
of an error. It should follow the rules for error names described
in the D-Bus specification, subsection <ulink
url="http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names">Valid
Names</ulink>. A number of common, standardized error names are
described in
<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
but additional domain-specific errors may be defined by
applications. The <structfield>message</structfield> field usually
contains a human-readable string describing the details, but might
be <constant>NULL</constant>. An unset <structname>sd_bus_error</structname> structure
should have both fields initialized to <constant>NULL</constant>. Set an error
structure to <constant>SD_BUS_ERROR_NULL</constant> in order to
reset both fields to <constant>NULL</constant>. When no longer necessary, resources
held by the <structname>sd_bus_error</structname> structure should
be destroyed with <function>sd_bus_error_free()</function>.</para>
<para>The <structname>sd_bus_error</structname> 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.
<itemizedlist>
<listitem><para>The <structfield>name</structfield> field contains a short identifier of an error. It
should follow the rules for error names described in the D-Bus specification, subsection <ulink
url="http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names">Valid
Names</ulink>. A number of common, standardized error names are described in
<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>, but
additional domain-specific errors may be defined by applications.</para></listitem>
<para><function>sd_bus_error_set()</function> 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
<varname>errno</varname>-like negative value (see <citerefentry
<listitem><para>The <structfield>message</structfield> field usually contains a human-readable string
describing the details, but might be <constant>NULL</constant>.</para></listitem>
</itemizedlist>
An unset <structname>sd_bus_error</structname> structure should have both fields initialized to
<constant>NULL</constant>, and signifies lack of an error, i.e. success. Assign
<constant>SD_BUS_ERROR_NULL</constant> to the structure in order to initialize both fields to
<constant>NULL</constant>. When no longer necessary, resources held by the
<structname>sd_bus_error</structname> structure should be destroyed with
<function>sd_bus_error_free()</function>.</para>
<para><function>sd_bus_error_set()</function> 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 <function>sd_bus_error_free()</function> first.</para>
<para><function>sd_bus_error_set()</function> will return an <varname>errno</varname>-like value (see
<citerefentry
project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
determined from the specified error name. Various well-known
D-Bus errors are converted to well-known <varname>errno</varname>
counterparts, and the other ones to <constant>-EIO</constant>. See
<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for a list of well-known error names. Additional error mappings
may be defined with
<citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
<parameter>e</parameter> is <constant>NULL</constant>, no error structure is initialized,
but the error is still converted into an
<varname>errno</varname>-style error. If
<parameter>name</parameter> is <constant>NULL</constant>, it is
assumed that no error occurred, and 0 is returned. This means that
this function may be conveniently used in a
<function>return</function> statement. If
<parameter>message</parameter> is <constant>NULL</constant>, no message is set. This
call can fail if no memory may be allocated for the name and
message strings, in which case an
<constant>SD_BUS_ERROR_NO_MEMORY</constant> 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
<function>sd_bus_error_free()</function> first.</para>
determined from the specified error name <parameter>name</parameter>. If <parameter>name</parameter> is
<constant>NULL</constant>, it is assumed that no error occurred, and <constant>0</constant> is returned.
If <parameter>name</parameter> is nonnull, a negative value is always returned. If
<parameter>e</parameter> is <constant>NULL</constant>, no error structure is initialized, but
<parameter>name</parameter> is still converted into an <varname>errno</varname>-style value.</para>
<para>Various well-known D-Bus errors are converted to well-known <varname>errno</varname> counterparts,
and the other ones to <constant>-EIO</constant>. See
<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry> for a
list of well-known error names. Additional error mappings may be defined with
<citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
<para><function>sd_bus_error_set()</function> is designed to be conveniently used in a
<function>return</function> statement. If <parameter>message</parameter> is <constant>NULL</constant>, no
message is set. This call can fail if no memory may be allocated for the name and message strings, in
which case an <constant>SD_BUS_ERROR_NO_MEMORY</constant> error will be set instead and
<constant>-ENOMEM</constant> returned. </para>
<para><function>sd_bus_error_setf()</function> is similar to
<function>sd_bus_error_set()</function>, but takes a <citerefentry
@ -204,33 +203,25 @@
<structfield>message</structfield> field.</para>
<para><function>sd_bus_error_set_const()</function> is similar to
<function>sd_bus_error_set()</function>, but the string parameters
are not copied internally, and must hence remain constant and
valid for the lifetime of <parameter>e</parameter>. 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
<function>sd_bus_error_set()</function> can, as described
above. Alternatively, the
<constant>SD_BUS_ERROR_MAKE_CONST()</constant> macro may be used
to generate a literal, constant bus error structure
on-the-fly.</para>
<function>sd_bus_error_set()</function>, but the string parameters are not copied internally, and must
hence remain constant and valid for the lifetime of <parameter>e</parameter>. 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 <function>sd_bus_error_set()</function> may, as described
above. Alternatively, the <constant>SD_BUS_ERROR_MAKE_CONST()</constant> macro may be used to generate a
literal, constant bus error structure on-the-fly.</para>
<para><function>sd_bus_error_set_errno()</function> will set
<structfield>name</structfield> from an
<varname>errno</varname>-like value that is converted to a D-Bus
<para><function>sd_bus_error_set_errno()</function> will immediately return <constant>0</constant> if the
specified error parameter <parameter>error</parameter> is <constant>0</constant>. Otherwise, it will set
<structfield>name</structfield> from an <varname>errno</varname>-like value that is converted to a D-Bus
error. <citerefentry
project='die-net'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry>
will be used to set <structfield>message</structfield>. Well-known
D-Bus error names will be used for <structfield>name</structfield>
if applicable, otherwise a name in the
<literal>System.Error.</literal> 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 <function>return</function> statements. This
call might fail due to lack of memory, in which case an
<constant>SD_BUS_ERROR_NO_MEMORY</constant> error is set instead,
and -ENOMEM is returned.</para>
project='die-net'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry> will
be used to set <structfield>message</structfield>. Well-known D-Bus error names will be used for
<structfield>name</structfield> if applicable, otherwise a name in the <literal>System.Error.</literal>
namespace will be generated. The sign of the specified error number is ignored and the absolute value is
used implicitly. If the specified error <parameter>error</parameter> is non-zero, the call always returns
a negative value, for convenient usage in <function>return</function> statements. This call might fail
due to lack of memory, in which case an <constant>SD_BUS_ERROR_NO_MEMORY</constant> error is set instead,
and <constant>-ENOMEM</constant> is returned.</para>
<para><function>sd_bus_error_set_errnof()</function> is similar to
<function>sd_bus_error_set_errno()</function>, but in addition to
@ -246,28 +237,26 @@
project='man-pages'><refentrytitle>va_arg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
parameter list.</para>
<para><function>sd_bus_error_get_errno()</function> converts the
<structfield>name</structfield> field of an error structure to an
<varname>errno</varname>-like (positive) value using the same
rules as <function>sd_bus_error_set()</function>. If
<parameter>e</parameter> is <constant>NULL</constant>, 0 will be
returned.</para>
<para><function>sd_bus_error_get_errno()</function> converts the <structfield>name</structfield> field of
an error structure to an <varname>errno</varname>-like (positive) value using the same rules as
<function>sd_bus_error_set()</function>. If <parameter>e</parameter> is <constant>NULL</constant>,
<constant>0</constant> will be returned.</para>
<para><function>sd_bus_error_copy()</function> will initialize
<parameter>dst</parameter> using the values in
<parameter>e</parameter>. If the strings in
<parameter>e</parameter> were set using
<function>sd_bus_error_set_const()</function>, they will be shared.
Otherwise, they will be copied. Returns a converted
<varname>errno</varname>-like, negative error code.</para>
<para><function>sd_bus_error_copy()</function> will initialize <parameter>dst</parameter> using the
values in <parameter>e</parameter>, if <parameter>e</parameter> has been set with an error value before.
Otherwise, it will return immediately. If the strings in <parameter>e</parameter> were set using
<function>sd_bus_error_set_const()</function>, they will be shared. Otherwise, they will be
copied. Returns a converted <varname>errno</varname>-like, negative error code or <constant>0</constant>.
Before this call, <parameter>dst</parameter> must be unset, i.e. either freshly initialized with
<constant>NULL</constant> or reset using <function>sd_bus_error_free()</function>.</para>
<para><function>sd_bus_error_move()</function> is similar to <function>sd_bus_error_copy()</function>, but will
move any error information from <parameter>e</parameter> into <parameter>dst</parameter>, resetting the
former. This function cannot fail, as no new memory is allocated. Note that if <parameter>e</parameter> is not set
(or <constant>NULL</constant>) <parameter>dst</parameter> is initializated to
<constant>SD_BUS_ERROR_NULL</constant>. Moreover, if <parameter>dst</parameter> is <constant>NULL</constant> no
operation is executed on it and resources held by <parameter>e</parameter> are freed and reset. Returns a
converted <varname>errno</varname>-like, negative error code.</para>
<para><function>sd_bus_error_move()</function> is similar to <function>sd_bus_error_copy()</function>,
but will move any error information from <parameter>e</parameter> into <parameter>dst</parameter>,
resetting the former. This function cannot fail, as no new memory is allocated. Note that if
<parameter>e</parameter> is not set, <parameter>dst</parameter> is initializated to
<constant>SD_BUS_ERROR_NULL</constant>. Moreover, if <parameter>dst</parameter> is
<constant>NULL</constant> no operation is executed on it and resources held by <parameter>e</parameter>
are freed and reset. Returns a converted <varname>errno</varname>-like, non-positive error value.</para>
<para><function>sd_bus_error_is_set()</function> will return a
non-zero value if <parameter>e</parameter> is
@ -300,25 +289,23 @@
<refsect1>
<title>Return Value</title>
<para>The functions <function>sd_bus_error_set()</function>,
<function>sd_bus_error_setf()</function>, and
<function>sd_bus_error_set_const()</function>, when successful,
return the negative errno value corresponding to the
<parameter>name</parameter> parameter. The functions
<function>sd_bus_error_set_errno()</function>,
<function>sd_bus_error_set_errnof()</function> and
<function>sd_bus_error_set_errnofv()</function>, when successful,
return the negative value of the <parameter>error</parameter>
parameter. If an error occurs, one of the negative error values
listed below will be returned.</para>
<para>The functions <function>sd_bus_error_set()</function>, <function>sd_bus_error_setf()</function>,
and <function>sd_bus_error_set_const()</function> always return <constant>0</constant> when the specified
error value is <constant>NULL</constant>, and a negative errno-like value corresponding to the
<parameter>name</parameter> parameter otherwise. The functions
<function>sd_bus_error_set_errno()</function>, <function>sd_bus_error_set_errnof()</function> and
<function>sd_bus_error_set_errnofv()</function>, return <constant>0</constant> when the specified error
value is <constant>0</constant>, and a a negative errno-like value corresponding to the
<parameter>error</parameter> parameter otherwise. If an error occurs internally, one of the negative
error values listed below will be returned.</para>
<para><function>sd_bus_error_get_errno()</function> returns
<constant>false</constant> when <parameter>e</parameter> is
<constant>NULL</constant>, and a positive errno value mapped from
<parameter>e-&gt;name</parameter> otherwise.</para>
<para><function>sd_bus_error_copy()</function> and <function>sd_bus_error_move()</function> return 0 or a positive
integer on success, and a negative error value converted from the error name otherwise.</para>
<para><function>sd_bus_error_copy()</function> and <function>sd_bus_error_move()</function> return a
negative error value converted from the source error, and zero if the error has not been set.</para>
<para><function>sd_bus_error_is_set()</function> returns a
non-zero value when <parameter>e</parameter> and the

2
src/libsystemd/sd-bus/bus-error.c
View file

@ -465,7 +465,7 @@ _public_ int sd_bus_error_set_errno(sd_bus_error *e, int error) {
if (!e)
return -error;
if (error == 0)
return -error;
return 0;
assert_return(!bus_error_is_dirty(e), -EINVAL);