MD: add a new disk role to present write journal device

Next patches will use a disk as raid5/6 journaling. We need a new disk
role to present the journal device and add MD_FEATURE_JOURNAL to
feature_map for backward compability.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>

3 files changed, 29 insertions, 2 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index cfe5c8704a26..391341a772c7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1638,6 +1638,15 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
                 case MD_DISK_ROLE_FAULTY: /* faulty */
                         set_bit(Faulty, &rdev->flags);
                         break;
+                case MD_DISK_ROLE_JOURNAL: /* journal device */
+                        if (!(le32_to_cpu(sb->feature_map) & MD_FEATURE_JOURNAL)) {
+                                /* journal device without journal feature */
+                                printk(KERN_WARNING
+                                  "md: journal device provided without journal feature, ignoring the device\n");
+                                return -EINVAL;
+                        }
+                        set_bit(Journal, &rdev->flags);
+                        break;
                 default:
                         rdev->saved_raid_disk = role;
                         if ((le32_to_cpu(sb->feature_map) &
@@ -1796,7 +1805,10 @@ retry:
                         sb->dev_roles[i] = cpu_to_le16(MD_DISK_ROLE_FAULTY);
                 else if (test_bit(In_sync, &rdev2->flags))
                         sb->dev_roles[i] = cpu_to_le16(rdev2->raid_disk);
-                else if (rdev2->raid_disk >= 0)
+                else if (test_bit(Journal, &rdev2->flags)) {
+                        sb->dev_roles[i] = cpu_to_le16(MD_DISK_ROLE_JOURNAL);
+                        sb->feature_map |= cpu_to_le32(MD_FEATURE_JOURNAL);
+                } else if (rdev2->raid_disk >= 0)
                         sb->dev_roles[i] = cpu_to_le16(rdev2->raid_disk);
                 else
                         sb->dev_roles[i] = cpu_to_le16(MD_DISK_ROLE_SPARE);
@@ -5840,7 +5852,8 @@ static int get_disk_info(struct mddev *mddev, void __user * arg)
                 else if (test_bit(In_sync, &rdev->flags)) {
                         info.state |= (1<<MD_DISK_ACTIVE);
                         info.state |= (1<<MD_DISK_SYNC);
-                }
+                } else if (test_bit(Journal, &rdev->flags))
+                        info.state |= (1<<MD_DISK_JOURNAL);
                 if (test_bit(WriteMostly, &rdev->flags))
                         info.state |= (1<<MD_DISK_WRITEMOSTLY);
         } else {
@@ -5955,6 +5968,8 @@ static int add_new_disk(struct mddev *mddev, mdu_disk_info_t *info)
                 else
                         clear_bit(WriteMostly, &rdev->flags);
 
+                if (info->state & (1<<MD_DISK_JOURNAL))
+                        set_bit(Journal, &rdev->flags);
                 /*
                  * check whether the device shows up in other nodes
                  */
@@ -7330,6 +7345,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
                                 seq_printf(seq, "(F)");
                                 continue;
                         }
+                        if (test_bit(Journal, &rdev->flags)) {
+                                seq_printf(seq, "(J)");
+                                continue;
+                        }
                         if (rdev->raid_disk < 0)
                                 seq_printf(seq, "(S)"); /* spare */
                         if (test_bit(Replacement, &rdev->flags))
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 2ea00356bb23..88dc6312f5d5 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -172,6 +172,11 @@ enum flag_bits {
                                  * This device is seen locally but not
                                  * by the whole cluster
                                  */
+        Journal,                /* This device is used as journal for
+                                 * raid-5/6.
+                                 * Usually, this device should be faster
+                                 * than other devices in the array
+                                 */
 };
 
 #define BB_LEN_MASK     (0x00000000000001FFULL)
diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
index d1fc8a637368..eaaab52077a3 100644
--- a/include/uapi/linux/raid/md_p.h
+++ b/include/uapi/linux/raid/md_p.h
@@ -89,9 +89,11 @@
                                    * read requests will only be sent here in
                                    * dire need
                                    */
+#define MD_DISK_JOURNAL         18 /* disk is used as the write journal in RAID-5/6 */
 
 #define MD_DISK_ROLE_SPARE      0xffff
 #define MD_DISK_ROLE_FAULTY     0xfffe
+#define MD_DISK_ROLE_JOURNAL    0xfffd
 #define MD_DISK_ROLE_MAX        0xff00 /* max value of regular disk role */
 
 typedef struct mdp_device_descriptor_s {
@@ -307,6 +309,7 @@ struct mdp_superblock_1 {
                                              * is guided by bitmap.
                                              */
 #define MD_FEATURE_CLUSTERED            256 /* clustered MD */
+#define MD_FEATURE_JOURNAL              512 /* support write cache */
 #define MD_FEATURE_ALL                  (MD_FEATURE_BITMAP_OFFSET       \
                                         |MD_FEATURE_RECOVERY_OFFSET     \
                                         |MD_FEATURE_RESHAPE_ACTIVE      \