[dm-devel] [PATCH] dm flakey: document corrupt_bio_byte and optional feature precedence

[Mike Snitzer <snitzer redhat com>]

Signed-off-by: Mike Snitzer <snitzer redhat com>
---
 Documentation/device-mapper/dm-flakey.txt |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/Documentation/device-mapper/dm-flakey.txt b/Documentation/device-mapper/dm-flakey.txt
index 6b40f79..6b4df49 100644
--- a/Documentation/device-mapper/dm-flakey.txt
+++ b/Documentation/device-mapper/dm-flakey.txt
@@ -27,7 +27,20 @@ Mandatory parameters:
 
 Optional feature parameters:
   If no feature parameters are present, during the periods of
-  unreliability, all I/O returns errors.
+  unreliability, all I/O returns errors.  Optional features may be
+  combined (e.g. corrupt_bio_byte on READ and drop_writes).  Conflicting
+  features (e.g. corrupt_bio_byte on WRITE and drop_writes) are resolved
+  according to the following feature precedence (descending order):
+
+  corrupt_bio_byte <Nth byte> <bio_flags> <value>:
+	Corrupt bios that have specific bi_rw flag(s), e.g.: READ=0 or
+	REQ_WRITE=1|REQ_META=32, by writing <value> to the <Nth byte> of
+	bios that have data.
+	Examples:
+	1) corrupt 32nd byte in READ bios with the value 1:
+	   corrupt_bio_byte 32 0 1
+	2) corrupt 224th byte in WRITE|REQ_META bios with the value 0:
+	   corrupt_bio_byte 224 33 0
 
   drop_writes:
 	All write I/O is silently ignored.