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man: document fd ownership for sd-bus fd marshalling

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Fixes: #8003
This commit is contained in:
Lennart Poettering
2020-08-28 21:18:14 +02:00
committed by Daan De Meyer
parent a667ddf132
commit e2b40db616
3 changed files with 30 additions and 14 deletions
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14
man/sd_bus_message_read.xml
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@@ -73,7 +73,10 @@
should be read. See the table below for a complete list of allowed arguments and their types. Note that,
if the basic type is a pointer (e.g., <type>const char *</type> in the case of a string), the argument is
a pointer to a pointer, and also the pointer value that is written is only borrowed and the contents must
be copied if they are to be used after the end of the messages lifetime.</para>
be copied if they are to be used after the end of the messages lifetime. If the type is
<literal>h</literal> (UNIX file descriptor), the descriptor is not duplicated by this call and the
returned descriptor remains in possession of the message object, and needs to be duplicated by the caller
in order to keep an open reference to it after the message object is freed.</para>
<para>Each argument may also be <constant>NULL</constant>, in which case the value is read and ignored.
</para>
@@ -228,6 +231,15 @@ const char *s, *t, *u;
sd_bus_message_read(m, "a{is}", 3, &amp;i, &amp;s, &amp;j, &amp;t, &amp;k, &amp;u);
</programlisting>
<para>Read a single file descriptor, and duplicate it in order to keep it open after the message is
freed.</para>
<programlisting>sd_bus_message *m;
int fd, fd_copy;
sd_bus_message_read(m, "h", &amp;fd);
fd_copy = fcntl(fd, FD_DUPFD_CLOEXEC, 3);</programlisting>
</refsect1>
<refsect1>