dm flakey: add corrupt_bio_byte feature

Add corrupt_bio_byte feature to simulate corruption by overwriting a byte at a
specified position with a specified value during intervals when the device is
"down".

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/Documentation/device-mapper/dm-flakey.txt b/Documentation/device-mapper/dm-flakey.txt
index 1b66c868ee7e..6ff5c2327227 100644
--- a/Documentation/device-mapper/dm-flakey.txt
+++ b/Documentation/device-mapper/dm-flakey.txt
@@ -32,3 +32,22 @@ Optional feature parameters:
   drop_writes:
         All write I/O is silently ignored.
         Read I/O is handled correctly.
+
+  corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
+        During <down interval>, replace <Nth_byte> of the data of
+        each matching bio with <value>.
+
+    <Nth_byte>: The offset of the byte to replace.
+                Counting starts at 1, to replace the first byte.
+    <direction>: Either 'r' to corrupt reads or 'w' to corrupt writes.
+                 'w' is incompatible with drop_writes.
+    <value>: The value (from 0-255) to write.
+    <flags>: Perform the replacement only if bio->bi_rw has all the
+             selected flags set.
+
+Examples:
+  corrupt_bio_byte 32 r 1 0
+        - replaces the 32nd byte of READ bios with the value 1
+
+  corrupt_bio_byte 224 w 0 32
+        - replaces the 224th byte of REQ_META (=32) bios with the value 0