A reflink creates a snapshot of a file, that means the attributes
must be identical except for three exceptions - nlink, ino, and ctime.
As for time changes, Here is a brief description:
1. Source file:
1) atime: Ignore. Let the lazy atime code handle that.
2) mtime: don't touch.
3) ctime: If we change the tree (adding REFCOUNTED to at least one
extent), update it.
2. Destination file:
1) atime: ignore.
2) mtime: we want it to appear identical to the source.
3) ctime: update.
The idea here is that an ls -l will show the same time for the
src and target - it shows mtime. Backup software like rsync and tar
will treat the new file correctly too.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
2 major functions are added in this patch.
ocfs2_attach_refcount_tree will create a new refcount tree to the
old file if it doesn't have one and insert all the extent records
to the tree if they are not refcounted.
ocfs2_create_reflink_node will:
1. set the refcount tree to the new file.
2. call ocfs2_duplicate_extent_list which will iterate all the
extents for the old file, insert it to the new file and increase
the corresponding referennce count.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
When we truncate a file to a specific size which resides in a reflinked
cluster, we need to CoW it since ocfs2_zero_range_for_truncate will
zero the space after the size(just another type of write).
So we add a "max_cpos" in ocfs2_refcount_cow so that it will stop when
it hit the max cluster offset.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
During CoW, if the old extent record is refcounted, we allocate
som new clusters and do CoW. Actually we can have some improvement
here. If the old extent has refcount=1, that means now it is only
used by this file. So we don't need to allocate new clusters, just
remove the refcounted flag and it is OK. We also have to remove
it from the refcount tree while not deleting it.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
This patch try CoW support for a refcounted record.
the whole process will be:
1. Calculate how many clusters we need to CoW and where we start.
Extents that are not completely encompassed by the write will
be broken on 1MB boundaries.
2. Do CoW for the clusters with the help of page cache.
3. Change the b-tree structure with the new allocated clusters.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Add 'Decrement refcount for delete' in to the normal truncate
process. So for a refcounted extent record, call refcount rec
decrementation instead of cluster free.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Given a physical cpos and length, decrement the refcount
in the tree. If the refcount for any portion of the extent goes
to zero, that portion is queued for freeing.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Given a physical cpos and length, increment the refcount
in the tree. If the extent has not been seen before, a refcount
record is created for it. Refcount records may be merged or
split by this operation.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Implement locking around struct ocfs2_refcount_tree. This protects
all read/write operations on refcount trees. ocfs2_refcount_tree
has its own lock and its own caching_info, protecting buffers among
multiple nodes.
User must call ocfs2_lock_refcount_tree before his operation on
the tree and unlock it after that.
ocfs2_refcount_trees are referenced by the block number of the
refcount tree root block, So we create an rb-tree on the ocfs2_super
to look them up.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
refcount tree should use its own caching info so that when
we downconvert the refcount tree lock, we can drop all the
cached buffer head.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Tao Ma