<refnamediv>
<refname>sd_journal_get_fd</refname>
+ <refname>sd_journal_get_events</refname>
<refname>sd_journal_reliable_fd</refname>
<refname>sd_journal_process</refname>
<refname>sd_journal_wait</refname>
<paramdef>sd_journal* <parameter>j</parameter></paramdef>
</funcprototype>
+ <funcprototype>
+ <funcdef>int <function>sd_journal_get_events</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ </funcprototype>
+
<funcprototype>
<funcdef>int <function>sd_journal_reliable_fd</function></funcdef>
<paramdef>sd_journal* <parameter>j</parameter></paramdef>
<para><function>sd_journal_get_fd()</function> returns
a file descriptor that may be asynchronously polled in
- an external event loop and is signaled readable as
- soon as the journal changes, because new entries or
- files were added, rotation took place, or files have
- been deleted, and similar. The file descriptor is
- suitable for usage in
- <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
- where it will yield POLLIN on changes. The call takes
- one argument: the journal context object. Note that
- not all file systems are capable of generating the
- necessary events for wakeups from this file descriptor
- to be enirely reliable. In particular network files
- systems do not generate suitable file change events in
- all cases. In such a case an application should not
- rely alone on wake-ups from this file descriptor but
- wake up and recheck the journal in regular time
- intervals, for example every 2s. To detect
- cases where this is necessary, use
+ an external event loop and is signaled as soon as the
+ journal changes, because new entries or files were
+ added, rotation took place, or files have been
+ deleted, and similar. The file descriptor is suitable
+ for usage in
+ <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>. Use
+ <function>sd_journal_get_events()</function> for an
+ events mask to watch for. The call takes one argument:
+ the journal context object. Note that not all file
+ systems are capable of generating the necessary events
+ for wakeups from this file descriptor to be enirely
+ reliable. In particular network files systems do not
+ generate suitable file change events in all cases. In
+ such a case an application should not rely alone on
+ wake-ups from this file descriptor but wake up and
+ recheck the journal in regular time intervals, for
+ example every 2s. To detect cases where this is
+ necessary, use
<function>sd_journal_reliable_fd()</function>,
below.</para>
+ <para><function>sd_journal_get_events()</function>
+ will return the
+ <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+ mask to wait for. This function will return a
+ combination of POLLIN and POLLOUT and similar to fill
+ into the <literal>.events</literal> field of
+ <literal>struct pollfd</literal>.</para>
+
<para><function>sd_journal_reliable_fd()</function>
may be used to check whether the wakeup events from
the file descriptor returned by
<function>sd_journal_get_fd()</function> are
sufficient as only source for wake-ups.</para>
- <para>After each POLLIN wake-up
+ <para>After each <literal>poll()</literal> wake-up
<function>sd_journal_process()</function> needs to be
- called to process events and reset the readable state
- of the file descriptor. This call will also indicate
+ called to process events. This call will also indicate
what kind of change has been detected (see below; note
that spurious wake-ups are possible).</para>
<para>A synchronous alternative for using
<function>sd_journal_get_fd()</function>,
+ <function>sd_journal_get_events()</function>,
<function>sd_journal_reliable_fd()</function> and
<function>sd_journal_process()</function> is
<function>sd_journal_wait()</function>. It will
<literal>(uint64_t) -1</literal> to wait
indefinitely. Internally this call simply combines
<function>sd_journal_get_fd()</function>,
+ <function>sd_journal_get_events()</function>,
<function>sd_journal_reliable_fd()</function>,
<function>poll()</function> and
<function>sd_journal_process()</function> into
one.</para>
-
</refsect1>
<refsect1>
<title>Return Value</title>
- <para><function>sd_journal_get_fd()</function> returns a valid file descriptor on success or a negative errno-style error
+ <para><function>sd_journal_get_fd()</function> returns
+ a valid file descriptor on success or a negative
+ errno-style error code.</para>
+
+ <para><function>sd_journal_get_events()</function>
+ returns a combination of POLLIN, POLLOUT and suchlike
+ on success or a negative errno-style error
code.</para>
<para><function>sd_journal_reliable_fd()</function>
<title>Notes</title>
<para>The <function>sd_journal_get_fd()</function>,
+ <function>sd_journal_get_events()</function>,
<function>sd_journal_reliable_fd()</function>,
<function>sd_journal_process()</function> and
<function>sd_journal_wait()</function> interfaces are
int wait_for_changes(sd_journal *j) {
struct pollfd pollfd;
pollfd.fd = sd_journal_get_fd(j);
- pollfd.events = POLLIN;
+ pollfd.events = sd_journal_get_events(j);
poll(&pollfd, 1, sd_journal_reliable_fd(j) > 0 ? -1 : 2000);
return sd_journal_process(j);
}
</programlisting>
</refsect1>
-
<refsect1>
<title>See Also</title>
~ianmdlvl / elogind.git / blobdiff