Btrfs: Add mount option to turn off data cow

A number of workloads do not require copy on write data or checksumming.
mount -o nodatasum to disable checksums and -o nodatacow to disable
both copy on write and checksumming.

In nodatacow mode, copy on write is still performed when a given extent
is under snapshot.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

5 files changed, 293 insertions, 25 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index fd8233e05cf4..585f279d1112 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -70,7 +70,58 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
         memset(p, 0, sizeof(*p));
 }
 
-static int __btrfs_cow_block(struct btrfs_trans_handle *trans,
+int btrfs_copy_root(struct btrfs_trans_handle *trans,
+                      struct btrfs_root *root,
+                      struct extent_buffer *buf,
+                      struct extent_buffer **cow_ret, u64 new_root_objectid)
+{
+        struct extent_buffer *cow;
+        u32 nritems;
+        int ret = 0;
+        int level;
+        struct btrfs_key first_key;
+        struct btrfs_root new_root;
+
+        memcpy(&new_root, root, sizeof(new_root));
+        new_root.root_key.objectid = new_root_objectid;
+
+        WARN_ON(root->ref_cows && trans->transid !=
+                root->fs_info->running_transaction->transid);
+        WARN_ON(root->ref_cows && trans->transid != root->last_trans);
+
+        level = btrfs_header_level(buf);
+        nritems = btrfs_header_nritems(buf);
+        if (nritems) {
+                if (level == 0)
+                        btrfs_item_key_to_cpu(buf, &first_key, 0);
+                else
+                        btrfs_node_key_to_cpu(buf, &first_key, 0);
+        } else {
+                first_key.objectid = 0;
+        }
+        cow = __btrfs_alloc_free_block(trans, &new_root, buf->len,
+                                       new_root_objectid,
+                                       trans->transid, first_key.objectid,
+                                       level, buf->start, 0);
+        if (IS_ERR(cow))
+                return PTR_ERR(cow);
+
+        copy_extent_buffer(cow, buf, 0, 0, cow->len);
+        btrfs_set_header_bytenr(cow, cow->start);
+        btrfs_set_header_generation(cow, trans->transid);
+        btrfs_set_header_owner(cow, new_root_objectid);
+
+        WARN_ON(btrfs_header_generation(buf) > trans->transid);
+        ret = btrfs_inc_ref(trans, &new_root, buf);
+        if (ret)
+                return ret;
+
+        btrfs_mark_buffer_dirty(cow);
+        *cow_ret = cow;
+        return 0;
+}
+
+int __btrfs_cow_block(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *buf,
                              struct extent_buffer *parent, int parent_slot,
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5e255cabfd10..b51b021fff85 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -431,6 +431,7 @@ struct btrfs_root {
 #define BTRFS_STRING_ITEM_KEY   253
 
 #define BTRFS_MOUNT_NODATASUM           0x1
+#define BTRFS_MOUNT_NODATACOW           0x2
 
 #define btrfs_clear_opt(o, opt)         ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)           ((o) |= BTRFS_MOUNT_##opt)
@@ -915,6 +916,9 @@ static inline u32 btrfs_level_size(struct btrfs_root *root, int level) {
         btrfs_item_offset_nr(leaf, slot)))
 
 /* extent-tree.c */
+u32 btrfs_count_snapshots_in_path(struct btrfs_root *root,
+                                  struct btrfs_path *count_path,
+                                  u64 first_extent);
 int btrfs_extent_post_op(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root);
 int btrfs_copy_pinned(struct btrfs_root *root, struct extent_map_tree *copy);
@@ -974,6 +978,10 @@ int btrfs_cow_block(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root, struct extent_buffer *buf,
                     struct extent_buffer *parent, int parent_slot,
                     struct extent_buffer **cow_ret);
+int btrfs_copy_root(struct btrfs_trans_handle *trans,
+                      struct btrfs_root *root,
+                      struct extent_buffer *buf,
+                      struct extent_buffer **cow_ret, u64 new_root_objectid);
 int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root
                       *root, struct btrfs_path *path, u32 data_size);
 int btrfs_truncate_item(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 00414836e963..1412d556313f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -679,6 +679,104 @@ out:
         return 0;
 }
 
+u32 btrfs_count_snapshots_in_path(struct btrfs_root *root,
+                                  struct btrfs_path *count_path,
+                                  u64 first_extent)
+{
+        struct btrfs_root *extent_root = root->fs_info->extent_root;
+        struct btrfs_path *path;
+        u64 bytenr;
+        u64 found_objectid;
+        u64 root_objectid = 0;
+        u32 total_count = 0;
+        u32 cur_count;
+        u32 refs;
+        u32 nritems;
+        int ret;
+        struct btrfs_key key;
+        struct btrfs_key found_key;
+        struct extent_buffer *l;
+        struct btrfs_extent_item *item;
+        struct btrfs_extent_ref *ref_item;
+        int level = -1;
+
+        path = btrfs_alloc_path();
+again:
+        if (level == -1)
+                bytenr = first_extent;
+        else
+                bytenr = count_path->nodes[level]->start;
+
+        cur_count = 0;
+        key.objectid = bytenr;
+        key.offset = 0;
+
+        btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
+        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
+        if (ret < 0)
+                goto out;
+        BUG_ON(ret == 0);
+
+        l = path->nodes[0];
+        btrfs_item_key_to_cpu(l, &found_key, path->slots[0]);
+
+        if (found_key.objectid != bytenr ||
+            found_key.type != BTRFS_EXTENT_ITEM_KEY) {
+                goto out;
+        }
+
+        item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
+        refs = btrfs_extent_refs(l, item);
+        while (1) {
+                nritems = btrfs_header_nritems(l);
+                if (path->slots[0] >= nritems) {
+                        ret = btrfs_next_leaf(extent_root, path);
+                        if (ret == 0)
+                                continue;
+                        break;
+                }
+                btrfs_item_key_to_cpu(l, &found_key, path->slots[0]);
+                if (found_key.objectid != bytenr)
+                        break;
+                if (found_key.type != BTRFS_EXTENT_REF_KEY) {
+                        path->slots[0]++;
+                        continue;
+                }
+
+                cur_count++;
+                ref_item = btrfs_item_ptr(l, path->slots[0],
+                                          struct btrfs_extent_ref);
+                found_objectid = btrfs_ref_root(l, ref_item);
+
+                if (found_objectid != root_objectid)
+                        total_count++;
+
+                if (total_count > 1)
+                        goto out;
+
+                if (root_objectid == 0)
+                        root_objectid = found_objectid;
+
+                path->slots[0]++;
+        }
+        if (cur_count == 0) {
+                total_count = 0;
+                goto out;
+        }
+        if (total_count > 1)
+                goto out;
+        if (level >= 0 && root->node == count_path->nodes[level])
+                goto out;
+        level++;
+        btrfs_release_path(root, path);
+        goto again;
+
+out:
+        btrfs_free_path(path);
+        return total_count;
+
+}
+
 int btrfs_inc_root_ref(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root, u64 owner_objectid)
 {
@@ -1127,9 +1225,6 @@ static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
         if (!path)
                 return -ENOMEM;
 
-        if (ref_generation && owner_objectid == 0 && root_objectid == 3) {
-//printk("drop backref root %Lu gen %Lu byte %Lu\n", root_objectid, ref_generation, bytenr );
-        }
         ret = lookup_extent_backref(trans, extent_root, path,
                                     bytenr, root_objectid,
                                     ref_generation,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 11885cb114e2..91f3fc43e2a9 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -72,21 +72,22 @@ static unsigned char btrfs_type_by_mode[S_IFMT >> S_SHIFT] = {
         [S_IFLNK >> S_SHIFT]    = BTRFS_FT_SYMLINK,
 };
 
-static int run_delalloc_range(struct inode *inode, u64 start, u64 end)
+static int cow_file_range(struct inode *inode, u64 start, u64 end)
 {
         struct btrfs_root *root = BTRFS_I(inode)->root;
         struct btrfs_trans_handle *trans;
-        struct btrfs_key ins;
         u64 alloc_hint = 0;
         u64 num_bytes;
-        int ret;
         u64 blocksize = root->sectorsize;
+        struct btrfs_key ins;
+        int ret;
 
-        mutex_lock(&root->fs_info->fs_mutex);
         trans = btrfs_start_transaction(root, 1);
-        btrfs_set_trans_block_group(trans, inode);
         BUG_ON(!trans);
+        btrfs_set_trans_block_group(trans, inode);
+
         num_bytes = (end - start + blocksize) & ~(blocksize - 1);
+        num_bytes = max(blocksize,  num_bytes);
         ret = btrfs_drop_extents(trans, root, inode,
                                  start, start + num_bytes, start, &alloc_hint);
 
@@ -106,6 +107,101 @@ static int run_delalloc_range(struct inode *inode, u64 start, u64 end)
                                        ins.offset);
 out:
         btrfs_end_transaction(trans, root);
+        return ret;
+}
+
+static int run_delalloc_nocow(struct inode *inode, u64 start, u64 end)
+{
+        u64 extent_start;
+        u64 extent_end;
+        u64 bytenr;
+        u64 cow_end;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        struct extent_buffer *leaf;
+        int found_type;
+        struct btrfs_path *path;
+        struct btrfs_file_extent_item *item;
+        int ret;
+        int err;
+        struct btrfs_key found_key;
+
+        path = btrfs_alloc_path();
+        BUG_ON(!path);
+again:
+        ret = btrfs_lookup_file_extent(NULL, root, path,
+                                       inode->i_ino, start, 0);
+        if (ret < 0) {
+                btrfs_free_path(path);
+                return ret;
+        }
+
+        cow_end = end;
+        if (ret != 0) {
+                if (path->slots[0] == 0)
+                        goto not_found;
+                path->slots[0]--;
+        }
+
+        leaf = path->nodes[0];
+        item = btrfs_item_ptr(leaf, path->slots[0],
+                              struct btrfs_file_extent_item);
+
+        /* are we inside the extent that was found? */
+        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+        found_type = btrfs_key_type(&found_key);
+        if (found_key.objectid != inode->i_ino ||
+            found_type != BTRFS_EXTENT_DATA_KEY) {
+                goto not_found;
+        }
+
+        found_type = btrfs_file_extent_type(leaf, item);
+        extent_start = found_key.offset;
+        if (found_type == BTRFS_FILE_EXTENT_REG) {
+                extent_end = extent_start +
+                       btrfs_file_extent_num_bytes(leaf, item);
+                err = 0;
+
+                if (start < extent_start || start >= extent_end)
+                        goto not_found;
+
+                cow_end = min(end, extent_end - 1);
+                bytenr = btrfs_file_extent_disk_bytenr(leaf, item);
+                if (bytenr == 0)
+                        goto not_found;
+
+                bytenr += btrfs_file_extent_offset(leaf, item);
+                if (btrfs_count_snapshots_in_path(root, path, bytenr) != 1) {
+                        goto not_found;
+                }
+
+                start = extent_end;
+        } else if (found_type == BTRFS_FILE_EXTENT_INLINE) {
+                goto not_found;
+        }
+loop:
+        if (start > end) {
+                btrfs_free_path(path);
+                return 0;
+        }
+        btrfs_release_path(root, path);
+        goto again;
+
+not_found:
+        cow_file_range(inode, start, cow_end);
+        start = cow_end + 1;
+        goto loop;
+}
+
+static int run_delalloc_range(struct inode *inode, u64 start, u64 end)
+{
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        int ret;
+
+        mutex_lock(&root->fs_info->fs_mutex);
+        if (btrfs_test_opt(root, NODATACOW))
+                ret = run_delalloc_nocow(inode, start, end);
+        else
+                ret = cow_file_range(inode, start, end);
         mutex_unlock(&root->fs_info->fs_mutex);
         return ret;
 }
@@ -1907,9 +2003,6 @@ int btrfs_commit_write(struct file *file, struct page *page,
 
         btrfs_cow_one_page(inode, page, PAGE_CACHE_SIZE);
 
-        set_page_extent_mapped(page);
-        set_page_dirty(page);
-
         if (pos > inode->i_size) {
                 i_size_write(inode, pos);
                 mark_inode_dirty(inode);
@@ -2078,13 +2171,18 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)
         key.objectid = objectid;
         key.offset = 1;
         btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
+
         extent_buffer_get(root->node);
         btrfs_cow_block(trans, root, root->node, NULL, 0, &tmp);
         free_extent_buffer(tmp);
-        btrfs_set_root_bytenr(&new_root_item, root->node->start);
-        btrfs_set_root_level(&new_root_item, btrfs_header_level(root->node));
+
+        btrfs_copy_root(trans, root, root->node, &tmp, objectid);
+
+        btrfs_set_root_bytenr(&new_root_item, tmp->start);
+        btrfs_set_root_level(&new_root_item, btrfs_header_level(tmp));
         ret = btrfs_insert_root(trans, root->fs_info->tree_root, &key,
                                 &new_root_item);
+        free_extent_buffer(tmp);
         if (ret)
                 goto fail;
 
@@ -2106,10 +2204,6 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)
 
         if (ret)
                 goto fail;
-
-        ret = btrfs_inc_root_ref(trans, root, objectid);
-        if (ret)
-                goto fail;
 fail:
         nr = trans->blocks_used;
         err = btrfs_commit_transaction(trans, root);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index ad4f280ec777..2116728d1f98 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -61,12 +61,13 @@ static void btrfs_put_super (struct super_block * sb)
 }
 
 enum {
-        Opt_subvol, Opt_nodatasum, Opt_err,
+        Opt_subvol, Opt_nodatasum, Opt_nodatacow, Opt_err,
 };
 
 static match_table_t tokens = {
         {Opt_subvol, "subvol=%s"},
         {Opt_nodatasum, "nodatasum"},
+        {Opt_nodatacow, "nodatacow"},
         {Opt_err, NULL}
 };
 
@@ -78,12 +79,20 @@ static int parse_options (char * options,
         struct btrfs_fs_info *info = NULL;
         substring_t args[MAX_OPT_ARGS];
 
-        if (root)
-                info = root->fs_info;
-
         if (!options)
                 return 1;
 
+        /*
+         * strsep changes the string, duplicate it because parse_options
+         * gets called twice
+         */
+        options = kstrdup(options, GFP_NOFS);
+        if (!options)
+                return -ENOMEM;
+
+        if (root)
+                info = root->fs_info;
+
         while ((p = strsep (&options, ",")) != NULL) {
                 int token;
                 if (!*p)
@@ -92,17 +101,28 @@ static int parse_options (char * options,
                 token = match_token(p, tokens, args);
                 switch (token) {
                 case Opt_subvol:
-                        if (subvol_name)
+                        if (subvol_name) {
                                 *subvol_name = match_strdup(&args[0]);
+                        }
                         break;
                 case Opt_nodatasum:
-                        if (root)
+                        if (info) {
+                                printk("btrfs: setting nodatacsum\n");
                                 btrfs_set_opt(info->mount_opt, NODATASUM);
+                        }
+                        break;
+                case Opt_nodatacow:
+                        if (info) {
+                                printk("btrfs: setting nodatacow\n");
+                                btrfs_set_opt(info->mount_opt, NODATACOW);
+                                btrfs_set_opt(info->mount_opt, NODATASUM);
+                        }
                         break;
                 default:
-                        return 0;
+                        break;
                 }
         }
+        kfree(options);
         return 1;
 }