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Btrfs: Add mount option to turn off data cow

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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>
This commit is contained in:
Chris Mason
2007-12-17 20:14:01 -05:00
parent b6cda9bcb4
commit be20aa9dba
5 changed files with 293 additions and 25 deletions
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122
fs/btrfs/inode.c
View File

@@ -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);