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man: add a note that FDSTORE=1 requires epoll-compatible fds

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Let's say that this was not obvious from our man page.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2016-10-22 20:32:59 -04:00
parent 16f70d6362
commit 99bdcdc7fc
2 changed files with 21 additions and 24 deletions
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41
man/sd_notify.xml
View File

@ -205,28 +205,25 @@
<varlistentry>
<term>FDSTORE=1</term>
<listitem><para>Stores additional file descriptors in the
service manager. File descriptors sent this way will be
maintained per-service by the service manager and be passed
again using the usual file descriptor passing logic on the
next invocation of the service (see
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
This is useful for implementing service restart schemes where
services serialize their state to <filename>/run</filename>,
push their file descriptors to the system manager, and are
then restarted, retrieving their state again via socket
passing and <filename>/run</filename>. Note that the service
manager will accept messages for a service only if
<varname>FileDescriptorStoreMax=</varname> is set to non-zero
for it (defaults to zero). See
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. Multiple arrays of file descriptors may be sent
in separate messages, in which case the arrays are combined.
Note that the service manager removes duplicate file
descriptors before passing them to the service. Use
<function>sd_pid_notify_with_fds()</function> to send messages
with <literal>FDSTORE=1</literal>, see
below.</para></listitem>
<listitem><para>Stores additional file descriptors in the service manager. File
descriptors sent this way will be maintained per-service by the service manager
and will be passed again using the usual file descriptor passing logic on the next
invocation of the service, see
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
This is useful for implementing service restart schemes where services serialize
their state to <filename>/run</filename>, push their file descriptors to the
system manager, and are then restarted, retrieving their state again via socket
passing and <filename>/run</filename>. Note that the service manager will accept
messages for a service only if <varname>FileDescriptorStoreMax=</varname> is set
to non-zero for it (defaults to zero, see
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
File descriptors must be pollable, see
<citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
Multiple arrays of file descriptors may be sent in separate messages, in which
case the arrays are combined. Note that the service manager removes duplicate
file descriptors before passing them to the service. Use
<function>sd_pid_notify_with_fds()</function> to send messages with
<literal>FDSTORE=1</literal>, see below.</para></listitem>
</varlistentry>
<varlistentry>

4
man/systemd.service.xml
View File

@ -852,13 +852,13 @@
serialized to <filename>/run</filename> and the file
descriptors passed to the service manager, to allow restarts
without losing state. Defaults to 0, i.e. no file descriptors
may be stored in the service manager by default. All file
may be stored in the service manager. All file
descriptors passed to the service manager from a specific
service are passed back to the service's main process on the
next service restart. Any file descriptors passed to the
service manager are automatically closed when POLLHUP or
POLLERR is seen on them, or when the service is fully stopped
and no job queued or being executed for it.</para></listitem>
and no job is queued or being executed for it.</para></listitem>
</varlistentry>
<varlistentry>