doc: add doc for cephfs lazyio

Fixes: http://tracker.ceph.com/issues/38729
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>

diff --git a/doc/cephfs/experimental-features.rst b/doc/cephfs/experimental-features.rst
index 7cd53be7e5bc49ee787475069f27b4f687b40154..3344a34d2a864918a03507ea9717f2bc36189b61 100644 (file)
--- a/doc/cephfs/experimental-features.rst
+++ b/doc/cephfs/experimental-features.rst
@@ -70,6 +70,11 @@ and may not work together; see above.
 Multiple filesystems were available starting in the Jewel release candidates
 but must be turned on via the ``enable_multiple`` flag until declared stable.
 
+LazyIO
+------
+LazyIO relaxes POSIX semantics. Buffered reads/writes are allowed even when a
+file is opened by multiple applications on multiple clients. Applications are
+responsible for managing cache coherency themselves.
 
 Previously experimental features
 ================================

diff --git a/doc/cephfs/index.rst b/doc/cephfs/index.rst
index c66f1168a448a8f511e36bac87583eec66a108d5..d55701d137d92fd31e49f537c250532af67084a8 100644 (file)
--- a/doc/cephfs/index.rst
+++ b/doc/cephfs/index.rst
@@ -110,6 +110,7 @@ authentication keyring.
     Export over NFS <nfs>
     Application best practices <app-best-practices>
     Scrub <scrub>
+    LazyIO <lazyio>
 
 .. toctree:: 
    :hidden:

diff --git a/doc/cephfs/lazyio.rst b/doc/cephfs/lazyio.rst
new file mode 100644 (file)
index 0000000..6737932
--- /dev/null
+++ b/doc/cephfs/lazyio.rst
@@ -0,0 +1,23 @@
+======
+LazyIO
+======
+
+LazyIO relaxes POSIX semantics. Buffered reads/writes are allowed even when a
+file is opened by multiple applications on multiple clients. Applications are
+responsible for managing cache coherency themselves.
+
+Libcephfs supports LazyIO since nautilus release.
+
+Enable LazyIO
+=============
+
+LazyIO can be enabled by following ways.
+
+- ``client_force_lazyio`` option enables LAZY_IO globally for libcephfs and
+  ceph-fuse mount.
+
+- ``ceph_lazyio(...)`` and ``ceph_ll_lazyio(...)`` enable LAZY_IO for file handle
+  in libcephfs.
+
+- ``ioctl(fd, CEPH_IOC_LAZYIO, 1UL)`` enables LAZY_IO for file handle in
+   ceph-fuse mount.