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Re: [dm-devel] [PATCH 1/9] dm snapshot: make chunk_io handle any buffer

On Wed, 29 Oct 2008 23:48:52 +0000
Alasdair G Kergon <agk redhat com> wrote:

> On Mon, Oct 27, 2008 at 09:07:48PM +0900, FUJITA Tomonori wrote:
> > chunk_io() can perform I/Os only with ps->area. This patch adds a new
> > argument (a pointer to a buffer) to chunk_io() so that it can performs
> > I/Os with the buffer.
> > +static int chunk_io(struct pstore *ps, chunk_t chunk, int rw, int metadata,
> > +		    void *data)
> data is part of ps so should not need passing in as it's already accessible!

The later patches uses chunk_io() to I/O for any data buffer (that is,
buffers are not in pstore).

> It's looking like struct pstore is acquiring fields that apply to only one
> type of snapshot:  IOW More-invasive refactoring of that struct is needed.
> - Which fields apply to both?  Which apply only to one type of snapshot?

The 7/9 patch adds the following fields to struct pstore:

 struct disk_exception {
@@ -131,6 +146,27 @@ struct pstore {
 	struct dm_io_client *io_client;
 	struct workqueue_struct *metadata_wq;
+	/*
+	 * for shared exception
+	 */
+	u64 root_tree_chunk;
+	u64 snapmask;
+	u32 tree_level;
+	u32 nr_snapshots;
+	unsigned long nr_chunks;
+	unsigned long nr_bitmap_chunks;
+	unsigned long *bitmap;
+	unsigned long cur_bitmap_chunk;
+	unsigned long cur_bitmap_index;
+	struct list_head chunk_buffer_list;
+	struct list_head chunk_buffer_dirty_list;
+	int header_dirty;
+	int nr_chunk_buffers;

The new snapshot code uses the following existing fields in struct

	void *zero_area;
	chunk_t current_area;
	chunk_t next_free;
	uint32_t current_committed;

Do you want to split struct pstore?


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