md: add raid4/5/6 journal mode switching API

Commit 2ded370373a4 ("md/r5cache: State machine for raid5-cache write
back mode") added support for "write-back" caching on the raid journal
device.

In order to allow the dm-raid target to switch between the available
"write-through" and "write-back" modes, provide a new
r5c_journal_mode_set() API.

Use the new API in existing r5c_journal_mode_store()

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Acked-by: Shaohua Li <shli@fb.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

2 files changed, 45 insertions, 28 deletions

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 3f307be01b10..218b6f37da85 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -53,16 +53,6 @@
  */
 #define R5L_POOL_SIZE   4
 
-/*
- * r5c journal modes of the array: write-back or write-through.
- * write-through mode has identical behavior as existing log only
- * implementation.
- */
-enum r5c_journal_mode {
-        R5C_JOURNAL_MODE_WRITE_THROUGH = 0,
-        R5C_JOURNAL_MODE_WRITE_BACK = 1,
-};
-
 static char *r5c_journal_mode_str[] = {"write-through",
                                        "write-back"};
 /*
@@ -2327,40 +2317,56 @@ static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
         return ret;
 }
 
-static ssize_t r5c_journal_mode_store(struct mddev *mddev,
-                                      const char *page, size_t length)
+/*
+ * Set journal cache mode on @mddev (external API initially needed by dm-raid).
+ *
+ * @mode as defined in 'enum r5c_journal_mode'.
+ *
+ */
+int r5c_journal_mode_set(struct mddev *mddev, int mode)
 {
         struct r5conf *conf = mddev->private;
         struct r5l_log *log = conf->log;
-        int val = -1, i;
-        int len = length;
 
         if (!log)
                 return -ENODEV;
 
-        if (len && page[len - 1] == '\n')
-                len -= 1;
-        for (i = 0; i < ARRAY_SIZE(r5c_journal_mode_str); i++)
-                if (strlen(r5c_journal_mode_str[i]) == len &&
-                    strncmp(page, r5c_journal_mode_str[i], len) == 0) {
-                        val = i;
-                        break;
-                }
-        if (val < R5C_JOURNAL_MODE_WRITE_THROUGH ||
-            val > R5C_JOURNAL_MODE_WRITE_BACK)
+        if (mode < R5C_JOURNAL_MODE_WRITE_THROUGH ||
+            mode > R5C_JOURNAL_MODE_WRITE_BACK)
                 return -EINVAL;
 
         if (raid5_calc_degraded(conf) > 0 &&
-            val == R5C_JOURNAL_MODE_WRITE_BACK)
+            mode == R5C_JOURNAL_MODE_WRITE_BACK)
                 return -EINVAL;
 
         mddev_suspend(mddev);
-        conf->log->r5c_journal_mode = val;
+        conf->log->r5c_journal_mode = mode;
         mddev_resume(mddev);
 
         pr_debug("md/raid:%s: setting r5c cache mode to %d: %s\n",
-                 mdname(mddev), val, r5c_journal_mode_str[val]);
-        return length;
+                 mdname(mddev), mode, r5c_journal_mode_str[mode]);
+        return 0;
+}
+EXPORT_SYMBOL(r5c_journal_mode_set);
+
+static ssize_t r5c_journal_mode_store(struct mddev *mddev,
+                                      const char *page, size_t length)
+{
+        int mode = ARRAY_SIZE(r5c_journal_mode_str);
+        size_t len = length;
+
+        if (len < 2)
+                return -EINVAL;
+
+        if (page[len - 1] == '\n')
+                len--;
+
+        while (mode--)
+                if (strlen(r5c_journal_mode_str[mode]) == len &&
+                    !strncmp(page, r5c_journal_mode_str[mode], len))
+                        break;
+
+        return r5c_journal_mode_set(mddev, mode) ?: length;
 }
 
 struct md_sysfs_entry
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 4bb27b97bf6b..ec8ca15774d7 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -547,6 +547,16 @@ struct r5worker_group {
         int stripes_cnt;
 };
 
+/*
+ * r5c journal modes of the array: write-back or write-through.
+ * write-through mode has identical behavior as existing log only
+ * implementation.
+ */
+enum r5c_journal_mode {
+        R5C_JOURNAL_MODE_WRITE_THROUGH = 0,
+        R5C_JOURNAL_MODE_WRITE_BACK = 1,
+};
+
 enum r5_cache_state {
         R5_INACTIVE_BLOCKED,    /* release of inactive stripes blocked,
                                  * waiting for 25% to be free
@@ -795,4 +805,5 @@ extern void r5c_check_cached_full_stripe(struct r5conf *conf);
 extern struct md_sysfs_entry r5c_journal_mode;
 extern void r5c_update_on_rdev_error(struct mddev *mddev);
 extern bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect);
+extern int r5c_journal_mode_set(struct mddev *mddev, int journal_mode);
 #endif