[PATCH v2] md/r5cache: journal remove support

[Song Liu <songliubraving@fb.com>]

When journal device of an array fails, the array is forced into read-only
mode. To make the array normal without adding another journal device, we
need to remove journal _feature_ from the array.

This patch allows remove journal _feature_ from an array, For journal
remove to work, existing journal should be either missing or faulty.

Two flags are added to GET_ARRAY_INFO for mdadm.
  1. MD_SB_HAS_JOURNAL: meaning the array have journal feature;
  2. MD_SB_JOURNAL_REMOVABLE: meaning the journal is faulty or missing

When both flags are set, mdadm can clear MD_SB_HAS_JOURNAL to remove
journal _feature_.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/md.c                | 44 ++++++++++++++++++++++++++++++++++++++++--
 include/uapi/linux/raid/md_p.h | 11 ++++++++---
 2 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index ac3bd15..14bf4c3 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5981,6 +5981,25 @@ static void autorun_devices(int part)
 }
 #endif /* !MODULE */
 
+/*
+ * the journal _feature_ is removable when:
+ * the array has journal support &&
+ *    (journal is missing || journal is faulty)
+ */
+static bool journal_removable(struct mddev *mddev)
+{
+	struct md_rdev *rdev;
+
+	if (!test_bit(MD_HAS_JOURNAL, &mddev->flags))
+		return false;
+
+	rdev_for_each_rcu(rdev, mddev)
+		if (test_bit(Journal, &rdev->flags) &&
+		    !test_bit(Faulty, &rdev->flags))
+		    return false;
+	return true;
+}
+
 static int get_version(void __user *arg)
 {
 	mdu_version_t ver;
@@ -6041,6 +6060,10 @@ static int get_array_info(struct mddev *mddev, void __user *arg)
 		info.state |= (1<<MD_SB_BITMAP_PRESENT);
 	if (mddev_is_clustered(mddev))
 		info.state |= (1<<MD_SB_CLUSTERED);
+	if (test_bit(MD_HAS_JOURNAL, &mddev->flags))
+		info.state |= (1<<MD_SB_HAS_JOURNAL);
+	if (journal_removable(mddev))
+		info.state |= (1<<MD_SB_JOURNAL_REMOVABLE);
 	info.active_disks  = insync;
 	info.working_disks = working;
 	info.failed_disks  = failed;
@@ -6721,6 +6744,10 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 	/* calculate expected state,ignoring low bits */
 	if (mddev->bitmap && mddev->bitmap_info.offset)
 		state |= (1 << MD_SB_BITMAP_PRESENT);
+	if (test_bit(MD_HAS_JOURNAL, &mddev->flags))
+		state |= (1 << MD_SB_HAS_JOURNAL);
+	if (journal_removable(mddev))
+		state |= (1 << MD_SB_JOURNAL_REMOVABLE);
 
 	if (mddev->major_version != info->major_version ||
 	    mddev->minor_version != info->minor_version ||
@@ -6730,8 +6757,11 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 /*	    mddev->layout        != info->layout        || */
 	    mddev->persistent	 != !info->not_persistent ||
 	    mddev->chunk_sectors != info->chunk_size >> 9 ||
-	    /* ignore bottom 8 bits of state, and allow SB_BITMAP_PRESENT to change */
-	    ((state^info->state) & 0xfffffe00)
+	    /*
+	     * ignore bottom 8 bits of state, and allow SB_BITMAP_PRESENT
+	     * and SB_HAS_JOURNAL to change
+	     */
+	    ((state^info->state) & 0xfffffc00)
 		)
 		return -EINVAL;
 	/* Check there is only one change */
@@ -6743,6 +6773,8 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 		cnt++;
 	if ((state ^ info->state) & (1<<MD_SB_BITMAP_PRESENT))
 		cnt++;
+	if ((state ^ info->state) & (1<<MD_SB_HAS_JOURNAL))
+		cnt++;
 	if (cnt == 0)
 		return 0;
 	if (cnt > 1)
@@ -6831,6 +6863,14 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 			mddev->bitmap_info.offset = 0;
 		}
 	}
+	if ((state ^ info->state) & (1<<MD_SB_HAS_JOURNAL)) {
+		if (!journal_removable(mddev)) {
+			rv = -EINVAL;
+			goto err;
+		}
+		clear_bit(MD_HAS_JOURNAL,  &mddev->flags);
+	}
+
 	md_update_sb(mddev, 1);
 	return rv;
 err:
diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
index d9a1ead..b1f2b63 100644
--- a/include/uapi/linux/raid/md_p.h
+++ b/include/uapi/linux/raid/md_p.h
@@ -1,15 +1,15 @@
 /*
    md_p.h : physical layout of Linux RAID devices
           Copyright (C) 1996-98 Ingo Molnar, Gadi Oxman
-	  
+
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2, or (at your option)
    any later version.
-   
+
    You should have received a copy of the GNU General Public License
    (for example /usr/src/linux/COPYING); if not, write to the Free
-   Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  
+   Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
 #ifndef _MD_P_H
@@ -119,6 +119,11 @@ typedef struct mdp_device_descriptor_s {
 
 #define	MD_SB_CLUSTERED		5 /* MD is clustered */
 #define	MD_SB_BITMAP_PRESENT	8 /* bitmap may be present nearby */
+#define	MD_SB_HAS_JOURNAL	9
+#define	MD_SB_JOURNAL_REMOVABLE	10 /* journal _feature_ can be removed,
+				    * which means the journal is either
+				    * missing or Faulty
+				    */
 
 /*
  * Notes:
-- 
2.9.3