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>

2 files changed, 159 insertions, 15 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
diff --git a/drivers/md/dm-flakey.c b/drivers/md/dm-flakey.c
index e7c4c2a64f4b..89f73ca22cfa 100644
--- a/drivers/md/dm-flakey.c
+++ b/drivers/md/dm-flakey.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2003 Sistina Software (UK) Limited.
- * Copyright (C) 2004, 2010 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2004, 2010-2011 Red Hat, Inc. All rights reserved.
  *
  * This file is released under the GPL.
  */
@@ -15,6 +15,9 @@
 
 #define DM_MSG_PREFIX "flakey"
 
+#define all_corrupt_bio_flags_match(bio, fc)    \
+        (((bio)->bi_rw & (fc)->corrupt_bio_flags) == (fc)->corrupt_bio_flags)
+
 /*
  * Flakey: Used for testing only, simulates intermittent,
  * catastrophic device failure.
@@ -26,6 +29,10 @@ struct flakey_c {
         unsigned up_interval;
         unsigned down_interval;
         unsigned long flags;
+        unsigned corrupt_bio_byte;
+        unsigned corrupt_bio_rw;
+        unsigned corrupt_bio_value;
+        unsigned corrupt_bio_flags;
 };
 
 enum feature_flag_bits {
@@ -40,7 +47,10 @@ static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
         const char *arg_name;
 
         static struct dm_arg _args[] = {
-                {0, 1, "Invalid number of feature args"},
+                {0, 6, "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"},
         };
 
         /* No feature arguments supplied. */
@@ -49,9 +59,9 @@ static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
 
         r = dm_read_arg_group(_args, as, &argc, &ti->error);
         if (r)
-                return -EINVAL;
+                return r;
 
-        while (argc && !r) {
+        while (argc) {
                 arg_name = dm_shift_arg(as);
                 argc--;
 
@@ -67,11 +77,61 @@ static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
                         continue;
                 }
 
+                /*
+                 * corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>
+                 */
+                if (!strcasecmp(arg_name, "corrupt_bio_byte")) {
+                        if (!argc)
+                                ti->error = "Feature corrupt_bio_byte requires parameters";
+
+                        r = dm_read_arg(_args + 1, as, &fc->corrupt_bio_byte, &ti->error);
+                        if (r)
+                                return r;
+                        argc--;
+
+                        /*
+                         * Direction r or w?
+                         */
+                        arg_name = dm_shift_arg(as);
+                        if (!strcasecmp(arg_name, "w"))
+                                fc->corrupt_bio_rw = WRITE;
+                        else if (!strcasecmp(arg_name, "r"))
+                                fc->corrupt_bio_rw = READ;
+                        else {
+                                ti->error = "Invalid corrupt bio direction (r or w)";
+                                return -EINVAL;
+                        }
+                        argc--;
+
+                        /*
+                         * Value of byte (0-255) to write in place of correct one.
+                         */
+                        r = dm_read_arg(_args + 2, as, &fc->corrupt_bio_value, &ti->error);
+                        if (r)
+                                return r;
+                        argc--;
+
+                        /*
+                         * Only corrupt bios with these flags set.
+                         */
+                        r = dm_read_arg(_args + 3, as, &fc->corrupt_bio_flags, &ti->error);
+                        if (r)
+                                return r;
+                        argc--;
+
+                        continue;
+                }
+
                 ti->error = "Unrecognised flakey feature requested";
-                r = -EINVAL;
+                return -EINVAL;
         }
 
-        return r;
+        if (test_bit(DROP_WRITES, &fc->flags) && (fc->corrupt_bio_rw == WRITE)) {
+                ti->error = "drop_writes is incompatible with corrupt_bio_byte with the WRITE flag set";
+                return -EINVAL;
+        }
+
+        return 0;
 }
 
 /*
@@ -80,6 +140,11 @@ static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
  *
  *   Feature args:
  *     [drop_writes]
+ *     [corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>]
+ *
+ *   Nth_byte starts from 1 for the first byte.
+ *   Direction is r for READ or w for WRITE.
+ *   bio_flags is ignored if 0.
  */
 static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
@@ -178,31 +243,64 @@ static void flakey_map_bio(struct dm_target *ti, struct bio *bio)
                 bio->bi_sector = flakey_map_sector(ti, bio->bi_sector);
 }
 
+static void corrupt_bio_data(struct bio *bio, struct flakey_c *fc)
+{
+        unsigned bio_bytes = bio_cur_bytes(bio);
+        char *data = bio_data(bio);
+
+        /*
+         * Overwrite the Nth byte of the data returned.
+         */
+        if (data && bio_bytes >= fc->corrupt_bio_byte) {
+                data[fc->corrupt_bio_byte - 1] = fc->corrupt_bio_value;
+
+                DMDEBUG("Corrupting data bio=%p by writing %u to byte %u "
+                        "(rw=%c bi_rw=%lu bi_sector=%llu cur_bytes=%u)\n",
+                        bio, fc->corrupt_bio_value, fc->corrupt_bio_byte,
+                        (bio_data_dir(bio) == WRITE) ? 'w' : 'r',
+                        bio->bi_rw, (unsigned long long)bio->bi_sector, bio_bytes);
+        }
+}
+
 static int flakey_map(struct dm_target *ti, struct bio *bio,
                       union map_info *map_context)
 {
         struct flakey_c *fc = ti->private;
         unsigned elapsed;
-        unsigned rw;
 
         /* Are we alive ? */
         elapsed = (jiffies - fc->start_time) / HZ;
         if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval) {
-                rw = bio_data_dir(bio);
+                /*
+                 * Flag this bio as submitted while down.
+                 */
+                map_context->ll = 1;
+
+                /*
+                 * Map reads as normal.
+                 */
+                if (bio_data_dir(bio) == READ)
+                        goto map_bio;
 
                 /*
-                 * Drop writes.  Map reads as normal.
+                 * Drop writes?
                  */
                 if (test_bit(DROP_WRITES, &fc->flags)) {
-                        if (rw == WRITE) {
-                                bio_endio(bio, 0);
-                                return DM_MAPIO_SUBMITTED;
-                        }
+                        bio_endio(bio, 0);
+                        return DM_MAPIO_SUBMITTED;
+                }
+
+                /*
+                 * Corrupt matching writes.
+                 */
+                if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == WRITE)) {
+                        if (all_corrupt_bio_flags_match(bio, fc))
+                                corrupt_bio_data(bio, fc);
                         goto map_bio;
                 }
 
                 /*
-                 * Default setting errors all I/O.
+                 * By default, error all I/O.
                  */
                 return -EIO;
         }
@@ -213,6 +311,24 @@ map_bio:
         return DM_MAPIO_REMAPPED;
 }
 
+static int flakey_end_io(struct dm_target *ti, struct bio *bio,
+                         int error, union map_info *map_context)
+{
+        struct flakey_c *fc = ti->private;
+        unsigned bio_submitted_while_down = map_context->ll;
+
+        /*
+         * Corrupt successful READs while in down state.
+         * If flags were specified, only corrupt those that match.
+         */
+        if (!error && bio_submitted_while_down &&
+            (bio_data_dir(bio) == READ) && (fc->corrupt_bio_rw == READ) &&
+            all_corrupt_bio_flags_match(bio, fc))
+                corrupt_bio_data(bio, fc);
+
+        return error;
+}
+
 static int flakey_status(struct dm_target *ti, status_type_t type,
                          char *result, unsigned int maxlen)
 {
@@ -231,9 +347,17 @@ static int flakey_status(struct dm_target *ti, status_type_t type,
                        fc->down_interval);
 
                 drop_writes = test_bit(DROP_WRITES, &fc->flags);
-                DMEMIT("%u ", drop_writes);
+                DMEMIT("%u ", drop_writes + (fc->corrupt_bio_byte > 0) * 5);
+
                 if (drop_writes)
                         DMEMIT("drop_writes ");
+
+                if (fc->corrupt_bio_byte)
+                        DMEMIT("corrupt_bio_byte %u %c %u %u ",
+                               fc->corrupt_bio_byte,
+                               (fc->corrupt_bio_rw == WRITE) ? 'w' : 'r',
+                               fc->corrupt_bio_value, fc->corrupt_bio_flags);
+
                 break;
         }
         return 0;
@@ -275,6 +399,7 @@ static struct target_type flakey_target = {
         .ctr    = flakey_ctr,
         .dtr    = flakey_dtr,
         .map    = flakey_map,
+        .end_io = flakey_end_io,
         .status = flakey_status,
         .ioctl  = flakey_ioctl,
         .merge  = flakey_merge,