Btrfs: Seed device support

Seed device is a special btrfs with SEEDING super flag
set and can only be mounted in read-only mode. Seed
devices allow people to create new btrfs on top of it.

The new FS contains the same contents as the seed device,
but it can be mounted in read-write mode.

This patch does the following:

1) split code in btrfs_alloc_chunk into two parts. The first part does makes
the newly allocated chunk usable, but does not do any operation that modifies
the chunk tree. The second part does the the chunk tree modifications. This
division is for the bootstrap step of adding storage to the seed device.

2) Update device management code to handle seed device.
The basic idea is: For an FS grown from seed devices, its
seed devices are put into a list. Seed devices are
opened on demand at mounting time. If any seed device is
missing or has been changed, btrfs kernel module will
refuse to mount the FS.

3) make btrfs_find_block_group not return NULL when all
block groups are read-only.

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

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index c4c6c127323b..5ff74282a620 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -177,6 +177,9 @@ struct btrfs_dev_item {
         /* type and info about this device */
         __le64 type;
 
+        /* expected generation for this device */
+        __le64 generation;
+
         /* grouping information for allocation decisions */
         __le32 dev_group;
 
@@ -188,6 +191,9 @@ struct btrfs_dev_item {
 
         /* btrfs generated uuid for this device */
         u8 uuid[BTRFS_UUID_SIZE];
+
+        /* uuid of FS who owns this device */
+        u8 fsid[BTRFS_UUID_SIZE];
 } __attribute__ ((__packed__));
 
 struct btrfs_stripe {
@@ -263,6 +269,7 @@ struct btrfs_header {
                                         sizeof(struct btrfs_item) - \
                                         sizeof(struct btrfs_file_extent_item))
 
+#define BTRFS_SUPER_FLAG_SEEDING (1ULL << 32)
 
 /*
  * this is a very generous portion of the super block, giving us
@@ -278,7 +285,7 @@ struct btrfs_header {
 struct btrfs_super_block {
         u8 csum[BTRFS_CSUM_SIZE];
         /* the first 4 fields must match struct btrfs_header */
-        u8 fsid[16];    /* FS specific uuid */
+        u8 fsid[BTRFS_FSID_SIZE];    /* FS specific uuid */
         __le64 bytenr; /* this block number */
         __le64 flags;
 
@@ -941,6 +948,7 @@ BTRFS_SETGET_FUNCS(device_id, struct btrfs_dev_item, devid, 64);
 BTRFS_SETGET_FUNCS(device_group, struct btrfs_dev_item, dev_group, 32);
 BTRFS_SETGET_FUNCS(device_seek_speed, struct btrfs_dev_item, seek_speed, 8);
 BTRFS_SETGET_FUNCS(device_bandwidth, struct btrfs_dev_item, bandwidth, 8);
+BTRFS_SETGET_FUNCS(device_generation, struct btrfs_dev_item, generation, 64);
 
 BTRFS_SETGET_STACK_FUNCS(stack_device_type, struct btrfs_dev_item, type, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_device_total_bytes, struct btrfs_dev_item,
@@ -960,12 +968,19 @@ BTRFS_SETGET_STACK_FUNCS(stack_device_seek_speed, struct btrfs_dev_item,
                          seek_speed, 8);
 BTRFS_SETGET_STACK_FUNCS(stack_device_bandwidth, struct btrfs_dev_item,
                          bandwidth, 8);
+BTRFS_SETGET_STACK_FUNCS(stack_device_generation, struct btrfs_dev_item,
+                         generation, 64);
 
 static inline char *btrfs_device_uuid(struct btrfs_dev_item *d)
 {
         return (char *)d + offsetof(struct btrfs_dev_item, uuid);
 }
 
+static inline char *btrfs_device_fsid(struct btrfs_dev_item *d)
+{
+        return (char *)d + offsetof(struct btrfs_dev_item, fsid);
+}
+
 BTRFS_SETGET_FUNCS(chunk_length, struct btrfs_chunk, length, 64);
 BTRFS_SETGET_FUNCS(chunk_owner, struct btrfs_chunk, owner, 64);
 BTRFS_SETGET_FUNCS(chunk_stripe_len, struct btrfs_chunk, stripe_len, 64);
@@ -1661,6 +1676,7 @@ int btrfs_reloc_tree_cache_ref(struct btrfs_trans_handle *trans,
                                struct extent_buffer *buf, u64 orig_start);
 int btrfs_add_dead_reloc_root(struct btrfs_root *root);
 int btrfs_cleanup_reloc_trees(struct btrfs_root *root);
+u64 btrfs_reduce_alloc_profile(struct btrfs_root *root, u64 flags);
 /* ctree.c */
 int btrfs_previous_item(struct btrfs_root *root,
                         struct btrfs_path *path, u64 min_objectid,