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>

1 files changed, 108 insertions, 14 deletions

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);