dm flakey: add an "error_reads"

dm-flakey returns error on reads if no other argument is specified. We
simplify the logic, introduce an "error_reads" argument and an ERROR_READS
flag.

If no argument is specified, we set ERROR_READS, so that it behaves just
like before this patch.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 Documentation/admin-guide/device-mapper/dm-flakey.rst |    4 ++
 drivers/md/dm-flakey.c                                |   28 ++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

Index: linux-2.6/Documentation/admin-guide/device-mapper/dm-flakey.rst
===================================================================
--- linux-2.6.orig/Documentation/admin-guide/device-mapper/dm-flakey.rst
+++ linux-2.6/Documentation/admin-guide/device-mapper/dm-flakey.rst
@@ -39,6 +39,10 @@ Optional feature parameters:
   If no feature parameters are present, during the periods of
   unreliability, all I/O returns errors.
 
+  error_reads:
+	All read I/O is failed with an error signalled.
+	Write I/O is handled correctly.
+
   drop_writes:
 	All write I/O is silently ignored.
 	Read I/O is handled correctly.
Index: linux-2.6/drivers/md/dm-flakey.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-flakey.c
+++ linux-2.6/drivers/md/dm-flakey.c
@@ -37,6 +37,7 @@ struct flakey_c {
 };
 
 enum feature_flag_bits {
+	ERROR_READS,
 	DROP_WRITES,
 	ERROR_WRITES
 };
@@ -53,7 +54,7 @@ static int parse_features(struct dm_arg_
 	const char *arg_name;
 
 	static const struct dm_arg _args[] = {
-		{0, 6, "Invalid number of feature args"},
+		{0, 7, "Invalid number of feature args"},
 		{1, UINT_MAX, "Invalid corrupt bio byte"},
 		{0, 255, "Invalid corrupt value to write into bio byte (0-255)"},
 		{0, UINT_MAX, "Invalid corrupt bio flags mask"},
@@ -77,6 +78,17 @@ static int parse_features(struct dm_arg_
 		}
 
 		/*
+		 * error_reads
+		 */
+		if (!strcasecmp(arg_name, "error_reads")) {
+			if (test_and_set_bit(ERROR_READS, &fc->flags)) {
+				ti->error = "Feature error_reads duplicated";
+				return -EINVAL;
+			}
+			continue;
+		}
+
+		/*
 		 * drop_writes
 		 */
 		if (!strcasecmp(arg_name, "drop_writes")) {
@@ -171,6 +183,12 @@ static int parse_features(struct dm_arg_
 		return -EINVAL;
 	}
 
+	if (!fc->corrupt_bio_byte && !test_bit(ERROR_READS, &fc->flags) &&
+	    !test_bit(DROP_WRITES, &fc->flags) && !test_bit(ERROR_WRITES, &fc->flags)) {
+		set_bit(ERROR_WRITES, &fc->flags);
+		set_bit(ERROR_READS, &fc->flags);
+	}
+
 	return 0;
 }
 
@@ -346,8 +364,7 @@ static int flakey_map(struct dm_target *
 		 * Otherwise, flakey_end_io() will decide if the reads should be modified.
 		 */
 		if (bio_data_dir(bio) == READ) {
-			if (!fc->corrupt_bio_byte && !test_bit(DROP_WRITES, &fc->flags) &&
-			    !test_bit(ERROR_WRITES, &fc->flags))
+			if (test_bit(ERROR_READS, &fc->flags))
 				return DM_MAPIO_KILL;
 			goto map_bio;
 		}
@@ -373,11 +390,6 @@ static int flakey_map(struct dm_target *
 			}
 			goto map_bio;
 		}
-
-		/*
-		 * By default, error all I/O.
-		 */
-		return DM_MAPIO_KILL;
 	}
 
 map_bio: