Implement support for flush, fua and rotational.

[nbd.git] / man / nbd-server.5.in.sgml

diff --git a/man/nbd-server.5.in.sgml b/man/nbd-server.5.in.sgml
index 9fb2eff..07ed9fd 100644 (file)
--- a/man/nbd-server.5.in.sgml
+++ b/man/nbd-server.5.in.sgml
@@ -410,6 +410,64 @@ manpage.1: manpage.sgml
        </listitem>
       </varlistentry>
       <varlistentry>
+        <term><option>flush</option></term>
+       <listitem>
+         <para>Optional; boolean.</para>
+         <para>When this option is enabled,
+           <command>nbd-server</command> will inform the client that it
+           supports and desires to be sent flush requests when the
+           elevator layer receives them. Receipt of a flush request
+           will cause an fdatasync() (or, if the sync option is set,
+           an fsync()) on the backend storage. This increases
+           reliability in the case of an unclean shutdown at
+           the expense of a degradation of performance. The default
+           state is disabled. This option will have no effect unless
+           supported by the client.
+         </para>
+       </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><option>fua</option></term>
+       <listitem>
+         <para>Optional; boolean.</para>
+         <para>When this option is enabled,
+           <command>nbd-server</command> will inform the client that it
+           supports and desires to be sent fua (force unit access) commands
+           when the elevator layer receives them. Receipt of a force unit
+           access command will cause the specified command to be synced
+           to backend storage using sync_file_range() if supported, or
+           fdatasync() otherwise. This increases
+           reliability in the case of an unclean shutdown at
+           the expense of a degradation of performance. The default
+           state is disabled. This option will have no effect unless
+           supported by the client.
+         </para>
+       </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><option>rotational</option></term>
+       <listitem>
+         <para>Optional; boolean.</para>
+         <para>When this option is enabled,
+           <command>nbd-server</command> will inform the client that it
+           it would prefer it to send requests in elevator order, perhaps
+           because it has a backing store and no local elevator. By
+           default, the client uses QUEUE_FLAG_NONROT, which effectively
+           restricts the function of the elevator to block merges. By
+           specifying this flag on the server, the client will not use
+           QUEUE_FLAG_NONROT, meaning the client elevator will perform
+           normal elevator ordering of I/O requests. Note that even when
+           the backing store is on rotating media, it is not normally
+           necessary to specify this flag, as the server's elevator
+           algorithm will be used. This flag is only required where
+           the server will not be using an elevator algorithm or where
+           the elevator algorithm is effectively neutered (e.g. with
+           the sync option set). This option will have no effect unless
+           supported by the client.
+         </para>
+       </listitem>
+      </varlistentry>
+      <varlistentry>
        <term><option>sparse_cow</option></term>
        <listitem>
          <para>Optional; boolean.</para>