2 files changed, 17 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index f3d418ba625e..0668f9dc9d29 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -309,6 +309,9 @@ Each directory contains:
               faulty   - device has been kicked from active use due to
                          a detected fault
               in_sync  - device is a fully in-sync member of the array
+              writemostly - device will only be subject to read
+                         requests if there are no other options.
+                         This applies only to raid1 arrays.
               spare    - device is working, but not a full member.
                          This includes spares that are in the process
                          of being recoverred to
@@ -316,6 +319,8 @@ Each directory contains:
         This can be written to.
         Writing "faulty"  simulates a failure on the device.
         Writing "remove" removes the device from the array.
+        Writing "writemostly" sets the writemostly flag.
+        Writing "-writemostly" clears the writemostly flag.
 
       errors
         An approximate count of read errors that have been detected on
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8603c0692eab..331b1bc95735 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1737,6 +1737,10 @@ state_show(mdk_rdev_t *rdev, char *page)
                 len += sprintf(page+len, "%sin_sync",sep);
                 sep = ",";
         }
+        if (test_bit(WriteMostly, &rdev->flags)) {
+                len += sprintf(page+len, "%swrite_mostly",sep);
+                sep = ",";
+        }
         if (!test_bit(Faulty, &rdev->flags) &&
             !test_bit(In_sync, &rdev->flags)) {
                 len += sprintf(page+len, "%sspare", sep);
@@ -1751,6 +1755,8 @@ state_store(mdk_rdev_t *rdev, const char *buf, size_t len)
         /* can write
          *  faulty  - simulates and error
          *  remove  - disconnects the device
+         *  writemostly - sets write_mostly
+         *  -writemostly - clears write_mostly
          */
         int err = -EINVAL;
         if (cmd_match(buf, "faulty") && rdev->mddev->pers) {
@@ -1766,6 +1772,12 @@ state_store(mdk_rdev_t *rdev, const char *buf, size_t len)
                         md_new_event(mddev);
                         err = 0;
                 }
+        } else if (cmd_match(buf, "writemostly")) {
+                set_bit(WriteMostly, &rdev->flags);
+                err = 0;
+        } else if (cmd_match(buf, "-writemostly")) {
+                clear_bit(WriteMostly, &rdev->flags);
+                err = 0;
         }
         return err ? err : len;
 }