[PATCH] doc: add "USAGE FILES" section to manpage

[Eric Wong <e@80x24.org>]

And fix formatting of the SIGNALS section while we're at it.
---
 cmogstored.x | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/cmogstored.x b/cmogstored.x
index 701fde9..b288e2d 100644
--- a/cmogstored.x
+++ b/cmogstored.x
@@ -1,5 +1,6 @@
 [SIGNALS]
 SIGQUIT - gracefully shutdown the server
+
 SIGUSR2 - upgrade executable on the fly
 
 [UPGRADING]
@@ -31,6 +32,20 @@ on inherited file descriptors being contiguous.
 See MALLOC TUNING for environment variables which may affect memory
 usage.
 
+[USAGE FILES]
+
+Like Perl mogstored(1), cmogstored writes "devNNN/usage" files for
+mogilefsd(1) instances to monitor disk space utilization.
+
+As of cmogstored 1.7, this information is stored in-memory in case the
+device becomes too full to write the usage file.  Users may choose to
+make usage files unwritable (via "chmod 000") to reduce disk wear on
+otherwise read-mostly devices.
+
+As of cmogstored 1.8, the in-memory representation of these usage files
+is updated by PUT and DELETE HTTP requests in case write traffic is too
+high for periodic (10s) updates.
+
 [MALLOC TUNING]
 
 malloc(3) implementations tuned for multithreading speed (and not memory