Btrfs: superblock duplication

This patch implements superblock duplication. Superblocks
are stored at offset 16K, 64M and 256G on every devices.
Spaces used by superblocks are preserved by the allocator,
which uses a reverse mapping function to find the logical
addresses that correspond to superblocks. Thank you,

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

1 files changed, 143 insertions, 65 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 61dc3b2c834b..c72f4f3b912c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1595,8 +1595,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
                      fs_info, BTRFS_ROOT_TREE_OBJECTID);
 
 
-        bh = __bread(fs_devices->latest_bdev,
-                     BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+        bh = btrfs_read_dev_super(fs_devices->latest_bdev);
         if (!bh)
                 goto fail_iput;
 
@@ -1710,7 +1709,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         }
 
         mutex_lock(&fs_info->chunk_mutex);
-        ret = btrfs_read_sys_array(tree_root);
+        ret = btrfs_read_sys_array(tree_root, btrfs_super_bytenr(disk_super));
         mutex_unlock(&fs_info->chunk_mutex);
         if (ret) {
                 printk("btrfs: failed to read the system array on %s\n",
@@ -1905,19 +1904,147 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
         put_bh(bh);
 }
 
-static int write_all_supers(struct btrfs_root *root)
+struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
+{
+        struct buffer_head *bh;
+        struct buffer_head *latest = NULL;
+        struct btrfs_super_block *super;
+        int i;
+        u64 transid = 0;
+        u64 bytenr;
+
+        /* we would like to check all the supers, but that would make
+         * a btrfs mount succeed after a mkfs from a different FS.
+         * So, we need to add a special mount option to scan for
+         * later supers, using BTRFS_SUPER_MIRROR_MAX instead
+         */
+        for (i = 0; i < 1; i++) {
+                bytenr = btrfs_sb_offset(i);
+                if (bytenr + 4096 >= i_size_read(bdev->bd_inode))
+                        break;
+                bh = __bread(bdev, bytenr / 4096, 4096);
+                if (!bh)
+                        continue;
+
+                super = (struct btrfs_super_block *)bh->b_data;
+                if (btrfs_super_bytenr(super) != bytenr ||
+                    strncmp((char *)(&super->magic), BTRFS_MAGIC,
+                            sizeof(super->magic))) {
+                        brelse(bh);
+                        continue;
+                }
+
+                if (!latest || btrfs_super_generation(super) > transid) {
+                        brelse(latest);
+                        latest = bh;
+                        transid = btrfs_super_generation(super);
+                } else {
+                        brelse(bh);
+                }
+        }
+        return latest;
+}
+
+static int write_dev_supers(struct btrfs_device *device,
+                            struct btrfs_super_block *sb,
+                            int do_barriers, int wait, int max_mirrors)
+{
+        struct buffer_head *bh;
+        int i;
+        int ret;
+        int errors = 0;
+        u32 crc;
+        u64 bytenr;
+        int last_barrier = 0;
+
+        if (max_mirrors == 0)
+                max_mirrors = BTRFS_SUPER_MIRROR_MAX;
+
+        /* make sure only the last submit_bh does a barrier */
+        if (do_barriers) {
+                for (i = 0; i < max_mirrors; i++) {
+                        bytenr = btrfs_sb_offset(i);
+                        if (bytenr + BTRFS_SUPER_INFO_SIZE >=
+                            device->total_bytes)
+                                break;
+                        last_barrier = i;
+                }
+        }
+
+        for (i = 0; i < max_mirrors; i++) {
+                bytenr = btrfs_sb_offset(i);
+                if (bytenr + BTRFS_SUPER_INFO_SIZE >= device->total_bytes)
+                        break;
+
+                if (wait) {
+                        bh = __find_get_block(device->bdev, bytenr / 4096,
+                                              BTRFS_SUPER_INFO_SIZE);
+                        BUG_ON(!bh);
+                        brelse(bh);
+                        wait_on_buffer(bh);
+                        if (buffer_uptodate(bh)) {
+                                brelse(bh);
+                                continue;
+                        }
+                } else {
+                        btrfs_set_super_bytenr(sb, bytenr);
+
+                        crc = ~(u32)0;
+                        crc = btrfs_csum_data(NULL, (char *)sb +
+                                              BTRFS_CSUM_SIZE, crc,
+                                              BTRFS_SUPER_INFO_SIZE -
+                                              BTRFS_CSUM_SIZE);
+                        btrfs_csum_final(crc, sb->csum);
+
+                        bh = __getblk(device->bdev, bytenr / 4096,
+                                      BTRFS_SUPER_INFO_SIZE);
+                        memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
+
+                        set_buffer_uptodate(bh);
+                        get_bh(bh);
+                        lock_buffer(bh);
+                        bh->b_end_io = btrfs_end_buffer_write_sync;
+                }
+
+                if (i == last_barrier && do_barriers && device->barriers) {
+                        ret = submit_bh(WRITE_BARRIER, bh);
+                        if (ret == -EOPNOTSUPP) {
+                                printk("btrfs: disabling barriers on dev %s\n",
+                                       device->name);
+                                set_buffer_uptodate(bh);
+                                device->barriers = 0;
+                                get_bh(bh);
+                                lock_buffer(bh);
+                                ret = submit_bh(WRITE, bh);
+                        }
+                } else {
+                        ret = submit_bh(WRITE, bh);
+                }
+
+                if (!ret && wait) {
+                        wait_on_buffer(bh);
+                        if (!buffer_uptodate(bh))
+                                errors++;
+                } else if (ret) {
+                        errors++;
+                }
+                if (wait)
+                        brelse(bh);
+        }
+        return errors < i ? 0 : -1;
+}
+
+int write_all_supers(struct btrfs_root *root, int max_mirrors)
 {
         struct list_head *cur;
         struct list_head *head = &root->fs_info->fs_devices->devices;
         struct btrfs_device *dev;
         struct btrfs_super_block *sb;
         struct btrfs_dev_item *dev_item;
-        struct buffer_head *bh;
         int ret;
         int do_barriers;
         int max_errors;
         int total_errors = 0;
-        u32 crc;
         u64 flags;
 
         max_errors = btrfs_super_num_devices(&root->fs_info->super_copy) - 1;
@@ -1944,40 +2071,11 @@ static int write_all_supers(struct btrfs_root *root)
                 btrfs_set_stack_device_sector_size(dev_item, dev->sector_size);
                 memcpy(dev_item->uuid, dev->uuid, BTRFS_UUID_SIZE);
                 memcpy(dev_item->fsid, dev->fs_devices->fsid, BTRFS_UUID_SIZE);
+
                 flags = btrfs_super_flags(sb);
                 btrfs_set_super_flags(sb, flags | BTRFS_HEADER_FLAG_WRITTEN);
 
-
-                crc = ~(u32)0;
-                crc = btrfs_csum_data(root, (char *)sb + BTRFS_CSUM_SIZE, crc,
-                                      BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
-                btrfs_csum_final(crc, sb->csum);
-
-                bh = __getblk(dev->bdev, BTRFS_SUPER_INFO_OFFSET / 4096,
-                              BTRFS_SUPER_INFO_SIZE);
-
-                memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
-                dev->pending_io = bh;
-
-                get_bh(bh);
-                set_buffer_uptodate(bh);
-                lock_buffer(bh);
-                bh->b_end_io = btrfs_end_buffer_write_sync;
-
-                if (do_barriers && dev->barriers) {
-                        ret = submit_bh(WRITE_BARRIER, bh);
-                        if (ret == -EOPNOTSUPP) {
-                                printk("btrfs: disabling barriers on dev %s\n",
-                                       dev->name);
-                                set_buffer_uptodate(bh);
-                                dev->barriers = 0;
-                                get_bh(bh);
-                                lock_buffer(bh);
-                                ret = submit_bh(WRITE, bh);
-                        }
-                } else {
-                        ret = submit_bh(WRITE, bh);
-                }
+                ret = write_dev_supers(dev, sb, do_barriers, 0, max_mirrors);
                 if (ret)
                         total_errors++;
         }
@@ -1985,8 +2083,8 @@ static int write_all_supers(struct btrfs_root *root)
                 printk("btrfs: %d errors while writing supers\n", total_errors);
                 BUG();
         }
-        total_errors = 0;
 
+        total_errors = 0;
         list_for_each(cur, head) {
                 dev = list_entry(cur, struct btrfs_device, dev_list);
                 if (!dev->bdev)
@@ -1994,29 +2092,9 @@ static int write_all_supers(struct btrfs_root *root)
                 if (!dev->in_fs_metadata || !dev->writeable)
                         continue;
 
-                BUG_ON(!dev->pending_io);
-                bh = dev->pending_io;
-                wait_on_buffer(bh);
-                if (!buffer_uptodate(dev->pending_io)) {
-                        if (do_barriers && dev->barriers) {
-                                printk("btrfs: disabling barriers on dev %s\n",
-                                       dev->name);
-                                set_buffer_uptodate(bh);
-                                get_bh(bh);
-                                lock_buffer(bh);
-                                dev->barriers = 0;
-                                ret = submit_bh(WRITE, bh);
-                                BUG_ON(ret);
-                                wait_on_buffer(bh);
-                                if (!buffer_uptodate(bh))
-                                        total_errors++;
-                        } else {
-                                total_errors++;
-                        }
-
-                }
-                dev->pending_io = NULL;
-                brelse(bh);
+                ret = write_dev_supers(dev, sb, do_barriers, 1, max_mirrors);
+                if (ret)
+                        total_errors++;
         }
         if (total_errors > max_errors) {
                 printk("btrfs: %d errors while writing supers\n", total_errors);
@@ -2025,12 +2103,12 @@ static int write_all_supers(struct btrfs_root *root)
         return 0;
 }
 
-int write_ctree_super(struct btrfs_trans_handle *trans, struct btrfs_root
-                      *root)
+int write_ctree_super(struct btrfs_trans_handle *trans,
+                      struct btrfs_root *root, int max_mirrors)
 {
         int ret;
 
-        ret = write_all_supers(root);
+        ret = write_all_supers(root, max_mirrors);
         return ret;
 }
 
@@ -2116,7 +2194,7 @@ int btrfs_commit_super(struct btrfs_root *root)
         ret = btrfs_write_and_wait_transaction(NULL, root);
         BUG_ON(ret);
 
-        ret = write_ctree_super(NULL, root);
+        ret = write_ctree_super(NULL, root, 0);
         return ret;
 }