[PATCH 3/3] md: bitmap: Support circular buffer list.

[Sean Fu]

Modify write_page free_buffers and read_page to support circular buffer
list.

Signed-off-by: Sean Fu <fxinr...@gmail.com>
---
 drivers/md/md-bitmap.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 239c7bb..b8412c2 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -286,7 +286,7 @@ static void bitmap_file_kick(struct bitmap *bitmap);
  */
 static void write_page(struct bitmap *bitmap, struct page *page, int wait)
 {
-       struct buffer_head *bh;
+       struct buffer_head *bh, *head;
 
        if (bitmap->storage.file == NULL) {
                switch (write_sb_page(bitmap, page, wait)) {
@@ -295,15 +295,16 @@ static void write_page(struct bitmap *bitmap, struct page 
*page, int wait)
                }
        } else {
 
-               bh = page_buffers(page);
+               bh = head = page_buffers(page);
 
-               while (bh && bh->b_blocknr) {
-                       atomic_inc(&bitmap->pending_writes);
-                       set_buffer_locked(bh);
-                       set_buffer_mapped(bh);
-                       submit_bh(REQ_OP_WRITE, REQ_SYNC, bh);
-                       bh = bh->b_this_page;
-               }
+               do {
+                       if (bh && bh->b_blocknr) {
+                               atomic_inc(&bitmap->pending_writes);
+                               set_buffer_locked(bh);
+                               set_buffer_mapped(bh);
+                               submit_bh(REQ_OP_WRITE, REQ_SYNC, bh);
+                       }
+               } while ((bh = bh->b_this_page) != head);
 
                if (wait)
                        wait_event(bitmap->write_wait,
@@ -333,17 +334,18 @@ __clear_page_buffers(struct page *page)
 }
 static void free_buffers(struct page *page)
 {
-       struct buffer_head *bh;
+       struct buffer_head *bh, *head;
 
        if (!PagePrivate(page))
                return;
 
-       bh = page_buffers(page);
-       while (bh) {
+       bh = head = page_buffers(page);
+       do {
                struct buffer_head *next = bh->b_this_page;
                free_buffer_head(bh);
                bh = next;
-       }
+       } while (bh != head);
+
        __clear_page_buffers(page);
        put_page(page);
 }
@@ -362,20 +364,20 @@ static int read_page(struct file *file, unsigned long 
index,
 {
        int ret = 0;
        struct inode *inode = file_inode(file);
-       struct buffer_head *bh;
+       struct buffer_head *bh, *head;
        sector_t block;
 
        pr_debug("read bitmap file (%dB @ %llu)\n", (int)PAGE_SIZE,
                 (unsigned long long)index << PAGE_SHIFT);
 
-       bh = alloc_page_buffers(page, 1<<inode->i_blkbits, false);
+       bh = head = alloc_page_buffers(page, 1<<inode->i_blkbits, false);
        if (!bh) {
                ret = -ENOMEM;
                goto out;
        }
        attach_page_buffers(page, bh);
        block = index << (PAGE_SHIFT - inode->i_blkbits);
-       while (bh) {
+       do {
                if (count == 0)
                        bh->b_blocknr = 0;
                else {
@@ -400,7 +402,7 @@ static int read_page(struct file *file, unsigned long index,
                }
                block++;
                bh = bh->b_this_page;
-       }
+       } while (bh != head);
        page->index = index;
 
        wait_event(bitmap->write_wait,
-- 
2.6.2