[PATCH] md: Set/get state of array via sysfs

This allows the state of an md/array to be directly controlled via sysfs and
adds the ability to stop and array without tearing it down.

Array states/settings:

 clear
     No devices, no size, no level
     Equivalent to STOP_ARRAY ioctl
 inactive
     May have some settings, but array is not active
        all IO results in error
     When written, doesn't tear down array, but just stops it
 suspended (not supported yet)
     All IO requests will block. The array can be reconfigured.
     Writing this, if accepted, will block until array is quiescent
 readonly
     no resync can happen.  no superblocks get written.
     write requests fail
 read-auto
     like readonly, but behaves like 'clean' on a write request.

 clean - no pending writes, but otherwise active.
     When written to inactive array, starts without resync
     If a write request arrives then
       if metadata is known, mark 'dirty' and switch to 'active'.
       if not known, block and switch to write-pending
     If written to an active array that has pending writes, then fails.
 active
     fully active: IO and resync can be happening.
     When written to inactive array, starts with resync

 write-pending (not supported yet)
     clean, but writes are blocked waiting for 'active' to be written.

 active-idle
     like active, but no writes have been seen for a while (100msec).

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index b19978e..df0b455 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -216,6 +216,45 @@ All md devices contain:
      period as a number of seconds.  The default is 200msec (0.200).
      Writing a value of 0 disables safemode.
 
+   array_state
+     This file contains a single word which describes the current
+     state of the array.  In many cases, the state can be set by
+     writing the word for the desired state, however some states
+     cannot be explicitly set, and some transitions are not allowed.
+
+     clear
+         No devices, no size, no level
+         Writing is equivalent to STOP_ARRAY ioctl
+     inactive
+         May have some settings, but array is not active
+            all IO results in error
+         When written, doesn't tear down array, but just stops it
+     suspended (not supported yet)
+         All IO requests will block. The array can be reconfigured.
+         Writing this, if accepted, will block until array is quiessent
+     readonly
+         no resync can happen.  no superblocks get written.
+         write requests fail
+     read-auto
+         like readonly, but behaves like 'clean' on a write request.
+
+     clean - no pending writes, but otherwise active.
+         When written to inactive array, starts without resync
+         If a write request arrives then
+           if metadata is known, mark 'dirty' and switch to 'active'.
+           if not known, block and switch to write-pending
+         If written to an active array that has pending writes, then fails.
+     active
+         fully active: IO and resync can be happening.
+         When written to inactive array, starts with resync
+
+     write-pending
+         clean, but writes are blocked waiting for 'active' to be written.
+
+     active-idle
+         like active, but no writes have been seen for a while (safe_mode_delay).
+
+
    sync_speed_min
    sync_speed_max
      This are similar to /proc/sys/dev/raid/speed_limit_{min,max}