This patch introduces uuids for subvolumes. Each
subvolume has it's own uuid. In case it was snapshotted,
it also contains parent_uuid. In case it was received,
it also contains received_uuid.

It also introduces subvolume ctime/otime/stime/rtime. The
first two are comparable to the times found in inodes. otime
is the origin/creation time and ctime is the change time.
stime/rtime are only valid on received subvolumes.
stime is the time of the subvolume when it was
sent. rtime is the time of the subvolume when it was
received.

Additionally to the times, we have a transid for each
time. They are updated at the same place as the times.

btrfs receive uses stransid and rtransid to find out
if a received subvolume changed in the meantime.

If an older kernel mounts a filesystem with the
extented fields, all fields become invalid. The next
mount with a new kernel will detect this and reset the
fields.

Signed-off-by: Alexander Block <abloc...@googlemail.com>
---
 fs/btrfs/ctree.h       |   43 ++++++++++++++++++++++
 fs/btrfs/disk-io.c     |    2 +
 fs/btrfs/inode.c       |    4 ++
 fs/btrfs/ioctl.c       |   96 ++++++++++++++++++++++++++++++++++++++++++++++--
 fs/btrfs/ioctl.h       |   13 +++++++
 fs/btrfs/root-tree.c   |   92 +++++++++++++++++++++++++++++++++++++++++++---
 fs/btrfs/transaction.c |   17 +++++++++
 7 files changed, 258 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 8cfde93..2bd5df8 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -709,6 +709,35 @@ struct btrfs_root_item {
        struct btrfs_disk_key drop_progress;
        u8 drop_level;
        u8 level;
+
+       /*
+        * The following fields appear after subvol_uuids+subvol_times
+        * were introduced.
+        */
+
+       /*
+        * This generation number is used to test if the new fields are valid
+        * and up to date while reading the root item. Everytime the root item
+        * is written out, the "generation" field is copied into this field. If
+        * anyone ever mounted the fs with an older kernel, we will have
+        * mismatching generation values here and thus must invalidate the
+        * new fields. See btrfs_update_root and btrfs_find_last_root for
+        * details.
+        * the offset of generation_v2 is also used as the start for the memset
+        * when invalidating the fields.
+        */
+       __le64 generation_v2;
+       u8 uuid[BTRFS_UUID_SIZE];
+       u8 parent_uuid[BTRFS_UUID_SIZE];
+       u8 received_uuid[BTRFS_UUID_SIZE];
+       __le64 ctransid; /* updated when an inode changes */
+       __le64 otransid; /* trans when created */
+       __le64 stransid; /* trans when sent. non-zero for received subvol */
+       __le64 rtransid; /* trans when received. non-zero for received subvol */
+       struct btrfs_timespec ctime;
+       struct btrfs_timespec otime;
+       struct btrfs_timespec stime;
+       struct btrfs_timespec rtime;
 } __attribute__ ((__packed__));
 
 /*
@@ -1416,6 +1445,8 @@ struct btrfs_root {
        dev_t anon_dev;
 
        int force_cow;
+
+       spinlock_t root_times_lock;
 };
 
 struct btrfs_ioctl_defrag_range_args {
@@ -2189,6 +2220,16 @@ BTRFS_SETGET_STACK_FUNCS(root_used, struct 
btrfs_root_item, bytes_used, 64);
 BTRFS_SETGET_STACK_FUNCS(root_limit, struct btrfs_root_item, byte_limit, 64);
 BTRFS_SETGET_STACK_FUNCS(root_last_snapshot, struct btrfs_root_item,
                         last_snapshot, 64);
+BTRFS_SETGET_STACK_FUNCS(root_generation_v2, struct btrfs_root_item,
+                        generation_v2, 64);
+BTRFS_SETGET_STACK_FUNCS(root_ctransid, struct btrfs_root_item,
+                        ctransid, 64);
+BTRFS_SETGET_STACK_FUNCS(root_otransid, struct btrfs_root_item,
+                        otransid, 64);
+BTRFS_SETGET_STACK_FUNCS(root_stransid, struct btrfs_root_item,
+                        stransid, 64);
+BTRFS_SETGET_STACK_FUNCS(root_rtransid, struct btrfs_root_item,
+                        rtransid, 64);
 
 static inline bool btrfs_root_readonly(struct btrfs_root *root)
 {
@@ -2829,6 +2870,8 @@ int btrfs_find_orphan_roots(struct btrfs_root *tree_root);
 void btrfs_set_root_node(struct btrfs_root_item *item,
                         struct extent_buffer *node);
 void btrfs_check_and_init_root_item(struct btrfs_root_item *item);
+void btrfs_update_root_times(struct btrfs_trans_handle *trans,
+                            struct btrfs_root *root);
 
 /* dir-item.c */
 int btrfs_insert_dir_item(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7b845ff..d3b49ad 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1182,6 +1182,8 @@ static void __setup_root(u32 nodesize, u32 leafsize, u32 
sectorsize,
        root->defrag_running = 0;
        root->root_key.objectid = objectid;
        root->anon_dev = 0;
+
+       spin_lock_init(&root->root_times_lock);
 }
 
 static int __must_check find_and_setup_root(struct btrfs_root *tree_root,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 139be17..0f6a65d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2734,6 +2734,8 @@ noinline int btrfs_update_inode(struct btrfs_trans_handle 
*trans,
         */
        if (!btrfs_is_free_space_inode(root, inode)
            && root->root_key.objectid != BTRFS_DATA_RELOC_TREE_OBJECTID) {
+               btrfs_update_root_times(trans, root);
+
                ret = btrfs_delayed_update_inode(trans, root, inode);
                if (!ret)
                        btrfs_set_inode_last_trans(trans, inode);
@@ -4728,6 +4730,8 @@ static struct inode *btrfs_new_inode(struct 
btrfs_trans_handle *trans,
        trace_btrfs_inode_new(inode);
        btrfs_set_inode_last_trans(trans, inode);
 
+       btrfs_update_root_times(trans, root);
+
        return inode;
 fail:
        if (dir)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 7011871..8d258cb 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -41,6 +41,7 @@
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
+#include <linux/uuid.h>
 #include "compat.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -346,11 +347,13 @@ static noinline int create_subvol(struct btrfs_root *root,
        struct btrfs_root *new_root;
        struct dentry *parent = dentry->d_parent;
        struct inode *dir;
+       struct timespec cur_time = CURRENT_TIME;
        int ret;
        int err;
        u64 objectid;
        u64 new_dirid = BTRFS_FIRST_FREE_OBJECTID;
        u64 index = 0;
+       uuid_le new_uuid;
 
        ret = btrfs_find_free_objectid(root->fs_info->tree_root, &objectid);
        if (ret)
@@ -389,8 +392,9 @@ static noinline int create_subvol(struct btrfs_root *root,
                            BTRFS_UUID_SIZE);
        btrfs_mark_buffer_dirty(leaf);
 
+       memset(&root_item, 0, sizeof(root_item));
+
        inode_item = &root_item.inode;
-       memset(inode_item, 0, sizeof(*inode_item));
        inode_item->generation = cpu_to_le64(1);
        inode_item->size = cpu_to_le64(3);
        inode_item->nlink = cpu_to_le32(1);
@@ -408,8 +412,15 @@ static noinline int create_subvol(struct btrfs_root *root,
        btrfs_set_root_used(&root_item, leaf->len);
        btrfs_set_root_last_snapshot(&root_item, 0);
 
-       memset(&root_item.drop_progress, 0, sizeof(root_item.drop_progress));
-       root_item.drop_level = 0;
+       btrfs_set_root_generation_v2(&root_item,
+                       btrfs_root_generation(&root_item));
+       uuid_le_gen(&new_uuid);
+       memcpy(root_item.uuid, new_uuid.b, BTRFS_UUID_SIZE);
+       root_item.otime.sec = cpu_to_le64(cur_time.tv_sec);
+       root_item.otime.nsec = cpu_to_le64(cur_time.tv_nsec);
+       root_item.ctime = root_item.otime;
+       btrfs_set_root_ctransid(&root_item, trans->transid);
+       btrfs_set_root_otransid(&root_item, trans->transid);
 
        btrfs_tree_unlock(leaf);
        free_extent_buffer(leaf);
@@ -3395,6 +3406,83 @@ out:
        return ret;
 }
 
+static long btrfs_ioctl_set_received_subvol(struct file *file,
+                                           void __user *arg)
+{
+       struct btrfs_ioctl_received_subvol_args *sa = NULL;
+       struct inode *inode = fdentry(file)->d_inode;
+       struct btrfs_root *root = BTRFS_I(inode)->root;
+       struct btrfs_root_item *root_item = &root->root_item;
+       struct btrfs_trans_handle *trans;
+       int ret = 0;
+
+       ret = mnt_want_write_file(file);
+       if (ret < 0)
+               return ret;
+
+       down_write(&root->fs_info->subvol_sem);
+
+       if (btrfs_ino(inode) != BTRFS_FIRST_FREE_OBJECTID) {
+               ret = -EINVAL;
+               goto out;
+       }
+
+       if (btrfs_root_readonly(root)) {
+               ret = -EROFS;
+               goto out;
+       }
+
+       if (!inode_owner_or_capable(inode)) {
+               ret = -EACCES;
+               goto out;
+       }
+
+       sa = memdup_user(arg, sizeof(*sa));
+       if (IS_ERR(sa)) {
+               ret = PTR_ERR(sa);
+               sa = NULL;
+               goto out;
+       }
+
+       trans = btrfs_start_transaction(root, 1);
+       if (IS_ERR(trans)) {
+               ret = PTR_ERR(trans);
+               trans = NULL;
+               goto out;
+       }
+
+       sa->rtransid = trans->transid;
+       sa->rtime = CURRENT_TIME;
+
+       memcpy(root_item->received_uuid, sa->uuid, BTRFS_UUID_SIZE);
+       btrfs_set_root_stransid(root_item, sa->stransid);
+       btrfs_set_root_rtransid(root_item, sa->rtransid);
+       root_item->stime.sec = cpu_to_le64(sa->stime.tv_sec);
+       root_item->stime.nsec = cpu_to_le64(sa->stime.tv_nsec);
+       root_item->rtime.sec = cpu_to_le64(sa->rtime.tv_sec);
+       root_item->rtime.nsec = cpu_to_le64(sa->rtime.tv_nsec);
+
+       ret = btrfs_update_root(trans, root->fs_info->tree_root,
+                               &root->root_key, &root->root_item);
+       if (ret < 0) {
+               goto out;
+       } else {
+               ret = btrfs_commit_transaction(trans, root);
+               if (ret < 0)
+                       goto out;
+       }
+
+       ret = copy_to_user(arg, sa, sizeof(*sa));
+       if (ret)
+               ret = -EFAULT;
+
+out:
+       kfree(sa);
+       up_write(&root->fs_info->subvol_sem);
+       mnt_drop_write_file(file);
+       return ret;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
                cmd, unsigned long arg)
 {
@@ -3477,6 +3565,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                return btrfs_ioctl_balance_ctl(root, arg);
        case BTRFS_IOC_BALANCE_PROGRESS:
                return btrfs_ioctl_balance_progress(root, argp);
+       case BTRFS_IOC_SET_RECEIVED_SUBVOL:
+               return btrfs_ioctl_set_received_subvol(file, argp);
        case BTRFS_IOC_GET_DEV_STATS:
                return btrfs_ioctl_get_dev_stats(root, argp, 0);
        case BTRFS_IOC_GET_AND_RESET_DEV_STATS:
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index e440aa6..c9e3fac 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -295,6 +295,15 @@ struct btrfs_ioctl_get_dev_stats {
        __u64 unused[128 - 2 - BTRFS_DEV_STAT_VALUES_MAX]; /* pad to 1k */
 };
 
+struct btrfs_ioctl_received_subvol_args {
+       char    uuid[BTRFS_UUID_SIZE];  /* in */
+       __u64   stransid;               /* in */
+       __u64   rtransid;               /* out */
+       struct timespec stime;          /* in */
+       struct timespec rtime;          /* out */
+       __u64   reserved[16];
+};
+
 #define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
                                   struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
@@ -359,6 +368,10 @@ struct btrfs_ioctl_get_dev_stats {
                                        struct btrfs_ioctl_ino_path_args)
 #define BTRFS_IOC_LOGICAL_INO _IOWR(BTRFS_IOCTL_MAGIC, 36, \
                                        struct btrfs_ioctl_ino_path_args)
+
+#define BTRFS_IOC_SET_RECEIVED_SUBVOL _IOWR(BTRFS_IOCTL_MAGIC, 37, \
+                               struct btrfs_ioctl_received_subvol_args)
+
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
                                      struct btrfs_ioctl_get_dev_stats)
 #define BTRFS_IOC_GET_AND_RESET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 53, \
diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 24fb8ce..17d638e 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -16,6 +16,7 @@
  * Boston, MA 021110-1307, USA.
  */
 
+#include <linux/uuid.h>
 #include "ctree.h"
 #include "transaction.h"
 #include "disk-io.h"
@@ -25,6 +26,9 @@
  * lookup the root with the highest offset for a given objectid.  The key we do
  * find is copied into 'key'.  If we find something return 0, otherwise 1, < 0
  * on error.
+ * We also check if the root was once mounted with an older kernel. If we 
detect
+ * this, the new fields coming after 'level' get overwritten with zeros so to
+ * invalidate the fields.
  */
 int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
                        struct btrfs_root_item *item, struct btrfs_key *key)
@@ -35,6 +39,9 @@ int btrfs_find_last_root(struct btrfs_root *root, u64 
objectid,
        struct extent_buffer *l;
        int ret;
        int slot;
+       int len;
+       int need_reset = 0;
+       uuid_le uuid;
 
        search_key.objectid = objectid;
        search_key.type = BTRFS_ROOT_ITEM_KEY;
@@ -60,11 +67,36 @@ int btrfs_find_last_root(struct btrfs_root *root, u64 
objectid,
                ret = 1;
                goto out;
        }
-       if (item)
+       if (item) {
+               len = btrfs_item_size_nr(l, slot);
                read_extent_buffer(l, item, btrfs_item_ptr_offset(l, slot),
-                                  sizeof(*item));
+                               min_t(int, len, (int)sizeof(*item)));
+               if (len < sizeof(*item))
+                       need_reset = 1;
+               if (!need_reset && btrfs_root_generation(item)
+                       != btrfs_root_generation_v2(item)) {
+                       if (btrfs_root_generation_v2(item) != 0) {
+                               printk(KERN_WARNING "btrfs: mismatching "
+                                               "generation and generation_v2 "
+                                               "found in root item. This root "
+                                               "was probably mounted with an "
+                                               "older kernel. Resetting all "
+                                               "new fields.\n");
+                       }
+                       need_reset = 1;
+               }
+               if (need_reset) {
+                       memset(&item->generation_v2, 0,
+                               sizeof(*item) - offsetof(struct btrfs_root_item,
+                                               generation_v2));
+
+                       uuid_le_gen(&uuid);
+                       memcpy(item->uuid, uuid.b, BTRFS_UUID_SIZE);
+               }
+       }
        if (key)
                memcpy(key, &found_key, sizeof(found_key));
+
        ret = 0;
 out:
        btrfs_free_path(path);
@@ -91,16 +123,15 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, 
struct btrfs_root
        int ret;
        int slot;
        unsigned long ptr;
+       int old_len;
 
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
 
        ret = btrfs_search_slot(trans, root, key, path, 0, 1);
-       if (ret < 0) {
-               btrfs_abort_transaction(trans, root, ret);
-               goto out;
-       }
+       if (ret < 0)
+               goto out_abort;
 
        if (ret != 0) {
                btrfs_print_leaf(root, path->nodes[0]);
@@ -113,11 +144,47 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, 
struct btrfs_root
        l = path->nodes[0];
        slot = path->slots[0];
        ptr = btrfs_item_ptr_offset(l, slot);
+       old_len = btrfs_item_size_nr(l, slot);
+
+       /*
+        * If this is the first time we update the root item which originated
+        * from an older kernel, we need to enlarge the item size to make room
+        * for the added fields.
+        */
+       if (old_len < sizeof(*item)) {
+               btrfs_release_path(path);
+               ret = btrfs_search_slot(trans, root, key, path,
+                               -1, 1);
+               if (ret < 0)
+                       goto out_abort;
+               ret = btrfs_del_item(trans, root, path);
+               if (ret < 0)
+                       goto out_abort;
+               btrfs_release_path(path);
+               ret = btrfs_insert_empty_item(trans, root, path,
+                               key, sizeof(*item));
+               if (ret < 0)
+                       goto out_abort;
+               l = path->nodes[0];
+               slot = path->slots[0];
+               ptr = btrfs_item_ptr_offset(l, slot);
+       }
+
+       /*
+        * Update generation_v2 so at the next mount we know the new root
+        * fields are valid.
+        */
+       btrfs_set_root_generation_v2(item, btrfs_root_generation(item));
+
        write_extent_buffer(l, item, ptr, sizeof(*item));
        btrfs_mark_buffer_dirty(path->nodes[0]);
 out:
        btrfs_free_path(path);
        return ret;
+
+out_abort:
+       btrfs_abort_transaction(trans, root, ret);
+       goto out;
 }
 
 int btrfs_insert_root(struct btrfs_trans_handle *trans, struct btrfs_root 
*root,
@@ -454,3 +521,16 @@ void btrfs_check_and_init_root_item(struct btrfs_root_item 
*root_item)
                root_item->byte_limit = 0;
        }
 }
+
+void btrfs_update_root_times(struct btrfs_trans_handle *trans,
+                            struct btrfs_root *root)
+{
+       struct btrfs_root_item *item = &root->root_item;
+       struct timespec ct = CURRENT_TIME;
+
+       spin_lock(&root->root_times_lock);
+       item->ctransid = trans->transid;
+       item->ctime.sec = cpu_to_le64(ct.tv_sec);
+       item->ctime.nsec = cpu_to_le64(ct.tv_nsec);
+       spin_unlock(&root->root_times_lock);
+}
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index b72b068..a21f308 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -22,6 +22,7 @@
 #include <linux/writeback.h>
 #include <linux/pagemap.h>
 #include <linux/blkdev.h>
+#include <linux/uuid.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -926,11 +927,13 @@ static noinline int create_pending_snapshot(struct 
btrfs_trans_handle *trans,
        struct dentry *dentry;
        struct extent_buffer *tmp;
        struct extent_buffer *old;
+       struct timespec cur_time = CURRENT_TIME;
        int ret;
        u64 to_reserve = 0;
        u64 index = 0;
        u64 objectid;
        u64 root_flags;
+       uuid_le new_uuid;
 
        rsv = trans->block_rsv;
 
@@ -1016,6 +1019,20 @@ static noinline int create_pending_snapshot(struct 
btrfs_trans_handle *trans,
                root_flags &= ~BTRFS_ROOT_SUBVOL_RDONLY;
        btrfs_set_root_flags(new_root_item, root_flags);
 
+       btrfs_set_root_generation_v2(new_root_item,
+                       trans->transid);
+       uuid_le_gen(&new_uuid);
+       memcpy(new_root_item->uuid, new_uuid.b, BTRFS_UUID_SIZE);
+       memcpy(new_root_item->parent_uuid, root->root_item.uuid,
+                       BTRFS_UUID_SIZE);
+       new_root_item->otime.sec = cpu_to_le64(cur_time.tv_sec);
+       new_root_item->otime.nsec = cpu_to_le64(cur_time.tv_nsec);
+       btrfs_set_root_otransid(new_root_item, trans->transid);
+       memset(&new_root_item->stime, 0, sizeof(new_root_item->stime));
+       memset(&new_root_item->rtime, 0, sizeof(new_root_item->rtime));
+       btrfs_set_root_stransid(new_root_item, 0);
+       btrfs_set_root_rtransid(new_root_item, 0);
+
        old = btrfs_lock_root_node(root);
        ret = btrfs_cow_block(trans, root, old, NULL, 0, &old);
        if (ret) {
-- 
1.7.10

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