Adding upstream version 14.2.21.upstream/14.2.21upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/doc/dev/context.rst b/doc/dev/context.rst
new file mode 100644
index 00000000..1a2b2cbf
--- /dev/null
+++ b/doc/dev/context.rst
@@ -0,0 +1,20 @@
+=============
+ CephContext
+=============
+
+A CephContext represents a single view of the Ceph cluster. It comes complete
+with a configuration, a set of performance counters (PerfCounters), and a
+heartbeat map. You can find more information about CephContext in
+src/common/ceph_context.h.
+
+Generally, you will have only one CephContext in your application, called
+g_ceph_context. However, in library code, it is possible that the library user
+will initialize multiple CephContexts. For example, this would happen if he
+called rados_create more than once.
+
+A ceph context is required to issue log messages. Why is this? Well, without
+the CephContext, we would not know which log messages were disabled and which
+were enabled.  The dout() macro implicitly references g_ceph_context, so it
+can't be used in library code.  It is fine to use dout and derr in daemons, but
+in library code, you must use ldout and lderr, and pass in your own CephContext
+object. The compiler will enforce this restriction.