nilfs2: buffer and page operations

This adds common routines for buffer/page operations used in B-tree
node caches, meta data files, or segment constructor (log writer).

NILFS uses copy functions for buffers and pages due to the following
reasons:

 1) Relocation required for COW
    Since NILFS changes address of on-disk blocks, moving buffers
    in page cache is needed for the buffers which are not addressed
    by a file offset.  If buffer size is smaller than page size,
    this involves partial copy of pages.

 2) Freezing mmapped pages
    NILFS calculates checksums for each log to ensure its validity.
    If page data changes after the checksum calculation, this validity
    check will not work correctly.  To avoid this failure for mmaped
    pages, NILFS freezes their data by copying.

 3) Copy-on-write for DAT pages
    NILFS makes clones of DAT page caches in a copy-on-write manner
    during GC processes, and this ensures atomicity and consistency
    of the DAT in the transient state.

In addition, NILFS uses two obsolete functions, nilfs_mark_buffer_dirty()
and nilfs_clear_page_dirty() respectively.

* nilfs_mark_buffer_dirty() was required to avoid NULL pointer
  dereference faults:

  Since the page cache of B-tree node pages or data page cache of pseudo
  inodes does not have a valid mapping->host, calling mark_buffer_dirty()
  for their buffers causes the fault; it calls __mark_inode_dirty(NULL)
  through __set_page_dirty().

* nilfs_clear_page_dirty() was needed in the two cases:

 1) For B-tree node pages and data pages of the dat/gcdat, NILFS2 clears
    page dirty flags when it copies back pages from the cloned cache
    (gcdat->{i_mapping,i_btnode_cache}) to its original cache
    (dat->{i_mapping,i_btnode_cache}).

 2) Some B-tree operations like insertion or deletion may dispose buffers
    in dirty state, and this needs to cancel the dirty state of their
    pages.  clear_page_dirty_for_io() caused faults because it does not
    clear the dirty tag on the page cache.

Signed-off-by: Seiji Kihara <kihara.seiji@lab.ntt.co.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 618 insertions, 0 deletions

diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
new file mode 100644
index 000000000000..7b18be8cd47a
--- /dev/null
+++ b/fs/nilfs2/page.c
@@ -0,0 +1,542 @@
+/*
+ * page.c - buffer/page management specific to NILFS
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Written by Ryusuke Konishi <ryusuke@osrg.net>,
+ *            Seiji Kihara <kihara@osrg.net>.
+ */
+
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+#include <linux/swap.h>
+#include <linux/bitops.h>
+#include <linux/page-flags.h>
+#include <linux/list.h>
+#include <linux/highmem.h>
+#include <linux/pagevec.h>
+#include "nilfs.h"
+#include "page.h"
+#include "mdt.h"
+
+
+#define NILFS_BUFFER_INHERENT_BITS  \
+        ((1UL << BH_Uptodate) | (1UL << BH_Mapped) | (1UL << BH_NILFS_Node) | \
+         (1UL << BH_NILFS_Volatile) | (1UL << BH_NILFS_Allocated))
+
+static struct buffer_head *
+__nilfs_get_page_block(struct page *page, unsigned long block, pgoff_t index,
+                       int blkbits, unsigned long b_state)
+
+{
+        unsigned long first_block;
+        struct buffer_head *bh;
+
+        if (!page_has_buffers(page))
+                create_empty_buffers(page, 1 << blkbits, b_state);
+
+        first_block = (unsigned long)index << (PAGE_CACHE_SHIFT - blkbits);
+        bh = nilfs_page_get_nth_block(page, block - first_block);
+
+        touch_buffer(bh);
+        wait_on_buffer(bh);
+        return bh;
+}
+
+/*
+ * Since the page cache of B-tree node pages or data page cache of pseudo
+ * inodes does not have a valid mapping->host pointer, calling
+ * mark_buffer_dirty() for their buffers causes a NULL pointer dereference;
+ * it calls __mark_inode_dirty(NULL) through __set_page_dirty().
+ * To avoid this problem, the old style mark_buffer_dirty() is used instead.
+ */
+void nilfs_mark_buffer_dirty(struct buffer_head *bh)
+{
+        if (!buffer_dirty(bh) && !test_set_buffer_dirty(bh))
+                __set_page_dirty_nobuffers(bh->b_page);
+}
+
+struct buffer_head *nilfs_grab_buffer(struct inode *inode,
+                                      struct address_space *mapping,
+                                      unsigned long blkoff,
+                                      unsigned long b_state)
+{
+        int blkbits = inode->i_blkbits;
+        pgoff_t index = blkoff >> (PAGE_CACHE_SHIFT - blkbits);
+        struct page *page, *opage;
+        struct buffer_head *bh, *obh;
+
+        page = grab_cache_page(mapping, index);
+        if (unlikely(!page))
+                return NULL;
+
+        bh = __nilfs_get_page_block(page, blkoff, index, blkbits, b_state);
+        if (unlikely(!bh)) {
+                unlock_page(page);
+                page_cache_release(page);
+                return NULL;
+        }
+        if (!buffer_uptodate(bh) && mapping->assoc_mapping != NULL) {
+                /*
+                 * Shadow page cache uses assoc_mapping to point its original
+                 * page cache.  The following code tries the original cache
+                 * if the given cache is a shadow and it didn't hit.
+                 */
+                opage = find_lock_page(mapping->assoc_mapping, index);
+                if (!opage)
+                        return bh;
+
+                obh = __nilfs_get_page_block(opage, blkoff, index, blkbits,
+                                             b_state);
+                if (buffer_uptodate(obh)) {
+                        nilfs_copy_buffer(bh, obh);
+                        if (buffer_dirty(obh)) {
+                                nilfs_mark_buffer_dirty(bh);
+                                if (!buffer_nilfs_node(bh) && NILFS_MDT(inode))
+                                        nilfs_mdt_mark_dirty(inode);
+                        }
+                }
+                brelse(obh);
+                unlock_page(opage);
+                page_cache_release(opage);
+        }
+        return bh;
+}
+
+/**
+ * nilfs_forget_buffer - discard dirty state
+ * @inode: owner inode of the buffer
+ * @bh: buffer head of the buffer to be discarded
+ */
+void nilfs_forget_buffer(struct buffer_head *bh)
+{
+        struct page *page = bh->b_page;
+
+        lock_buffer(bh);
+        clear_buffer_nilfs_volatile(bh);
+        if (test_clear_buffer_dirty(bh) && nilfs_page_buffers_clean(page))
+                __nilfs_clear_page_dirty(page);
+
+        clear_buffer_uptodate(bh);
+        clear_buffer_mapped(bh);
+        bh->b_blocknr = -1;
+        ClearPageUptodate(page);
+        ClearPageMappedToDisk(page);
+        unlock_buffer(bh);
+        brelse(bh);
+}
+
+/**
+ * nilfs_copy_buffer -- copy buffer data and flags
+ * @dbh: destination buffer
+ * @sbh: source buffer
+ */
+void nilfs_copy_buffer(struct buffer_head *dbh, struct buffer_head *sbh)
+{
+        void *kaddr0, *kaddr1;
+        unsigned long bits;
+        struct page *spage = sbh->b_page, *dpage = dbh->b_page;
+        struct buffer_head *bh;
+
+        kaddr0 = kmap_atomic(spage, KM_USER0);
+        kaddr1 = kmap_atomic(dpage, KM_USER1);
+        memcpy(kaddr1 + bh_offset(dbh), kaddr0 + bh_offset(sbh), sbh->b_size);
+        kunmap_atomic(kaddr1, KM_USER1);
+        kunmap_atomic(kaddr0, KM_USER0);
+
+        dbh->b_state = sbh->b_state & NILFS_BUFFER_INHERENT_BITS;
+        dbh->b_blocknr = sbh->b_blocknr;
+        dbh->b_bdev = sbh->b_bdev;
+
+        bh = dbh;
+        bits = sbh->b_state & ((1UL << BH_Uptodate) | (1UL << BH_Mapped));
+        while ((bh = bh->b_this_page) != dbh) {
+                lock_buffer(bh);
+                bits &= bh->b_state;
+                unlock_buffer(bh);
+        }
+        if (bits & (1UL << BH_Uptodate))
+                SetPageUptodate(dpage);
+        else
+                ClearPageUptodate(dpage);
+        if (bits & (1UL << BH_Mapped))
+                SetPageMappedToDisk(dpage);
+        else
+                ClearPageMappedToDisk(dpage);
+}
+
+/**
+ * nilfs_page_buffers_clean - check if a page has dirty buffers or not.
+ * @page: page to be checked
+ *
+ * nilfs_page_buffers_clean() returns zero if the page has dirty buffers.
+ * Otherwise, it returns non-zero value.
+ */
+int nilfs_page_buffers_clean(struct page *page)
+{
+        struct buffer_head *bh, *head;
+
+        bh = head = page_buffers(page);
+        do {
+                if (buffer_dirty(bh))
+                        return 0;
+                bh = bh->b_this_page;
+        } while (bh != head);
+        return 1;
+}
+
+void nilfs_page_bug(struct page *page)
+{
+        struct address_space *m;
+        unsigned long ino = 0;
+
+        if (unlikely(!page)) {
+                printk(KERN_CRIT "NILFS_PAGE_BUG(NULL)\n");
+                return;
+        }
+
+        m = page->mapping;
+        if (m) {
+                struct inode *inode = NILFS_AS_I(m);
+                if (inode != NULL)
+                        ino = inode->i_ino;
+        }
+        printk(KERN_CRIT "NILFS_PAGE_BUG(%p): cnt=%d index#=%llu flags=0x%lx "
+               "mapping=%p ino=%lu\n",
+               page, atomic_read(&page->_count),
+               (unsigned long long)page->index, page->flags, m, ino);
+
+        if (page_has_buffers(page)) {
+                struct buffer_head *bh, *head;
+                int i = 0;
+
+                bh = head = page_buffers(page);
+                do {
+                        printk(KERN_CRIT
+                               " BH[%d] %p: cnt=%d block#=%llu state=0x%lx\n",
+                               i++, bh, atomic_read(&bh->b_count),
+                               (unsigned long long)bh->b_blocknr, bh->b_state);
+                        bh = bh->b_this_page;
+                } while (bh != head);
+        }
+}
+
+/**
+ * nilfs_alloc_private_page - allocate a private page with buffer heads
+ *
+ * Return Value: On success, a pointer to the allocated page is returned.
+ * On error, NULL is returned.
+ */
+struct page *nilfs_alloc_private_page(struct block_device *bdev, int size,
+                                      unsigned long state)
+{
+        struct buffer_head *bh, *head, *tail;
+        struct page *page;
+
+        page = alloc_page(GFP_NOFS); /* page_count of the returned page is 1 */
+        if (unlikely(!page))
+                return NULL;
+
+        lock_page(page);
+        head = alloc_page_buffers(page, size, 0);
+        if (unlikely(!head)) {
+                unlock_page(page);
+                __free_page(page);
+                return NULL;
+        }
+
+        bh = head;
+        do {
+                bh->b_state = (1UL << BH_NILFS_Allocated) | state;
+                tail = bh;
+                bh->b_bdev = bdev;
+                bh = bh->b_this_page;
+        } while (bh);
+
+        tail->b_this_page = head;
+        attach_page_buffers(page, head);
+
+        return page;
+}
+
+void nilfs_free_private_page(struct page *page)
+{
+        BUG_ON(!PageLocked(page));
+        BUG_ON(page->mapping);
+
+        if (page_has_buffers(page) && !try_to_free_buffers(page))
+                NILFS_PAGE_BUG(page, "failed to free page");
+
+        unlock_page(page);
+        __free_page(page);
+}
+
+/**
+ * nilfs_copy_page -- copy the page with buffers
+ * @dst: destination page
+ * @src: source page
+ * @copy_dirty: flag whether to copy dirty states on the page's buffer heads.
+ *
+ * This fuction is for both data pages and btnode pages.  The dirty flag
+ * should be treated by caller.  The page must not be under i/o.
+ * Both src and dst page must be locked
+ */
+static void nilfs_copy_page(struct page *dst, struct page *src, int copy_dirty)
+{
+        struct buffer_head *dbh, *dbufs, *sbh, *sbufs;
+        unsigned long mask = NILFS_BUFFER_INHERENT_BITS;
+
+        BUG_ON(PageWriteback(dst));
+
+        sbh = sbufs = page_buffers(src);
+        if (!page_has_buffers(dst))
+                create_empty_buffers(dst, sbh->b_size, 0);
+
+        if (copy_dirty)
+                mask |= (1UL << BH_Dirty);
+
+        dbh = dbufs = page_buffers(dst);
+        do {
+                lock_buffer(sbh);
+                lock_buffer(dbh);
+                dbh->b_state = sbh->b_state & mask;
+                dbh->b_blocknr = sbh->b_blocknr;
+                dbh->b_bdev = sbh->b_bdev;
+                sbh = sbh->b_this_page;
+                dbh = dbh->b_this_page;
+        } while (dbh != dbufs);
+
+        copy_highpage(dst, src);
+
+        if (PageUptodate(src) && !PageUptodate(dst))
+                SetPageUptodate(dst);
+        else if (!PageUptodate(src) && PageUptodate(dst))
+                ClearPageUptodate(dst);
+        if (PageMappedToDisk(src) && !PageMappedToDisk(dst))
+                SetPageMappedToDisk(dst);
+        else if (!PageMappedToDisk(src) && PageMappedToDisk(dst))
+                ClearPageMappedToDisk(dst);
+
+        do {
+                unlock_buffer(sbh);
+                unlock_buffer(dbh);
+                sbh = sbh->b_this_page;
+                dbh = dbh->b_this_page;
+        } while (dbh != dbufs);
+}
+
+int nilfs_copy_dirty_pages(struct address_space *dmap,
+                           struct address_space *smap)
+{
+        struct pagevec pvec;
+        unsigned int i;
+        pgoff_t index = 0;
+        int err = 0;
+
+        pagevec_init(&pvec, 0);
+repeat:
+        if (!pagevec_lookup_tag(&pvec, smap, &index, PAGECACHE_TAG_DIRTY,
+                                PAGEVEC_SIZE))
+                return 0;
+
+        for (i = 0; i < pagevec_count(&pvec); i++) {
+                struct page *page = pvec.pages[i], *dpage;
+
+                lock_page(page);
+                if (unlikely(!PageDirty(page)))
+                        NILFS_PAGE_BUG(page, "inconsistent dirty state");
+
+                dpage = grab_cache_page(dmap, page->index);
+                if (unlikely(!dpage)) {
+                        /* No empty page is added to the page cache */
+                        err = -ENOMEM;
+                        unlock_page(page);
+                        break;
+                }
+                if (unlikely(!page_has_buffers(page)))
+                        NILFS_PAGE_BUG(page,
+                                       "found empty page in dat page cache");
+
+                nilfs_copy_page(dpage, page, 1);
+                __set_page_dirty_nobuffers(dpage);
+
+                unlock_page(dpage);
+                page_cache_release(dpage);
+                unlock_page(page);
+        }
+        pagevec_release(&pvec);
+        cond_resched();
+
+        if (likely(!err))
+                goto repeat;
+        return err;
+}
+
+/**
+ * nilfs_copy_back_pages -- copy back pages to orignal cache from shadow cache
+ * @dmap: destination page cache
+ * @smap: source page cache
+ *
+ * No pages must no be added to the cache during this process.
+ * This must be ensured by the caller.
+ */
+void nilfs_copy_back_pages(struct address_space *dmap,
+                           struct address_space *smap)
+{
+        struct pagevec pvec;
+        unsigned int i, n;
+        pgoff_t index = 0;
+        int err;
+
+        pagevec_init(&pvec, 0);
+repeat:
+        n = pagevec_lookup(&pvec, smap, index, PAGEVEC_SIZE);
+        if (!n)
+                return;
+        index = pvec.pages[n - 1]->index + 1;
+
+        for (i = 0; i < pagevec_count(&pvec); i++) {
+                struct page *page = pvec.pages[i], *dpage;
+                pgoff_t offset = page->index;
+
+                lock_page(page);
+                dpage = find_lock_page(dmap, offset);
+                if (dpage) {
+                        /* override existing page on the destination cache */
+                        BUG_ON(PageDirty(dpage));
+                        nilfs_copy_page(dpage, page, 0);
+                        unlock_page(dpage);
+                        page_cache_release(dpage);
+                } else {
+                        struct page *page2;
+
+                        /* move the page to the destination cache */
+                        spin_lock_irq(&smap->tree_lock);
+                        page2 = radix_tree_delete(&smap->page_tree, offset);
+                        if (unlikely(page2 != page))
+                                NILFS_PAGE_BUG(page, "page removal failed "
+                                               "(offset=%lu, page2=%p)",
+                                               offset, page2);
+                        smap->nrpages--;
+                        spin_unlock_irq(&smap->tree_lock);
+
+                        spin_lock_irq(&dmap->tree_lock);
+                        err = radix_tree_insert(&dmap->page_tree, offset, page);
+                        if (unlikely(err < 0)) {
+                                BUG_ON(err == -EEXIST);
+                                page->mapping = NULL;
+                                page_cache_release(page); /* for cache */
+                        } else {
+                                page->mapping = dmap;
+                                dmap->nrpages++;
+                                if (PageDirty(page))
+                                        radix_tree_tag_set(&dmap->page_tree,
+                                                           offset,
+                                                           PAGECACHE_TAG_DIRTY);
+                        }
+                        spin_unlock_irq(&dmap->tree_lock);
+                }
+                unlock_page(page);
+        }
+        pagevec_release(&pvec);
+        cond_resched();
+
+        goto repeat;
+}
+
+void nilfs_clear_dirty_pages(struct address_space *mapping)
+{
+        struct pagevec pvec;
+        unsigned int i;
+        pgoff_t index = 0;
+
+        pagevec_init(&pvec, 0);
+
+        while (pagevec_lookup_tag(&pvec, mapping, &index, PAGECACHE_TAG_DIRTY,
+                                  PAGEVEC_SIZE)) {
+                for (i = 0; i < pagevec_count(&pvec); i++) {
+                        struct page *page = pvec.pages[i];
+                        struct buffer_head *bh, *head;
+
+                        lock_page(page);
+                        ClearPageUptodate(page);
+                        ClearPageMappedToDisk(page);
+                        bh = head = page_buffers(page);
+                        do {
+                                lock_buffer(bh);
+                                clear_buffer_dirty(bh);
+                                clear_buffer_nilfs_volatile(bh);
+                                clear_buffer_uptodate(bh);
+                                clear_buffer_mapped(bh);
+                                unlock_buffer(bh);
+                                bh = bh->b_this_page;
+                        } while (bh != head);
+
+                        __nilfs_clear_page_dirty(page);
+                        unlock_page(page);
+                }
+                pagevec_release(&pvec);
+                cond_resched();
+        }
+}
+
+unsigned nilfs_page_count_clean_buffers(struct page *page,
+                                        unsigned from, unsigned to)
+{
+        unsigned block_start, block_end;
+        struct buffer_head *bh, *head;
+        unsigned nc = 0;
+
+        for (bh = head = page_buffers(page), block_start = 0;
+             bh != head || !block_start;
+             block_start = block_end, bh = bh->b_this_page) {
+                block_end = block_start + bh->b_size;
+                if (block_end > from && block_start < to && !buffer_dirty(bh))
+                        nc++;
+        }
+        return nc;
+}
+
+/*
+ * NILFS2 needs clear_page_dirty() in the following two cases:
+ *
+ * 1) For B-tree node pages and data pages of the dat/gcdat, NILFS2 clears
+ *    page dirty flags when it copies back pages from the shadow cache
+ *    (gcdat->{i_mapping,i_btnode_cache}) to its original cache
+ *    (dat->{i_mapping,i_btnode_cache}).
+ *
+ * 2) Some B-tree operations like insertion or deletion may dispose buffers
+ *    in dirty state, and this needs to cancel the dirty state of their pages.
+ */
+int __nilfs_clear_page_dirty(struct page *page)
+{
+        struct address_space *mapping = page->mapping;
+
+        if (mapping) {
+                spin_lock_irq(&mapping->tree_lock);
+                if (test_bit(PG_dirty, &page->flags)) {
+                        radix_tree_tag_clear(&mapping->page_tree,
+                                             page_index(page),
+                                             PAGECACHE_TAG_DIRTY);
+                        spin_unlock_irq(&mapping->tree_lock);
+                        return clear_page_dirty_for_io(page);
+                }
+                spin_unlock_irq(&mapping->tree_lock);
+                return 0;
+        }
+        return TestClearPageDirty(page);
+}
diff --git a/fs/nilfs2/page.h b/fs/nilfs2/page.h
new file mode 100644
index 000000000000..8abca4d1c1f8
--- /dev/null
+++ b/fs/nilfs2/page.h
@@ -0,0 +1,76 @@
+/*
+ * page.h - buffer/page management specific to NILFS
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Written by Ryusuke Konishi <ryusuke@osrg.net>,
+ *            Seiji Kihara <kihara@osrg.net>.
+ */
+
+#ifndef _NILFS_PAGE_H
+#define _NILFS_PAGE_H
+
+#include <linux/buffer_head.h>
+#include "nilfs.h"
+
+/*
+ * Extended buffer state bits
+ */
+enum {
+        BH_NILFS_Allocated = BH_PrivateStart,
+        BH_NILFS_Node,
+        BH_NILFS_Volatile,
+};
+
+BUFFER_FNS(NILFS_Allocated, nilfs_allocated)    /* nilfs private buffers */
+BUFFER_FNS(NILFS_Node, nilfs_node)              /* nilfs node buffers */
+BUFFER_FNS(NILFS_Volatile, nilfs_volatile)
+
+
+void nilfs_mark_buffer_dirty(struct buffer_head *bh);
+int __nilfs_clear_page_dirty(struct page *);
+
+struct buffer_head *nilfs_grab_buffer(struct inode *, struct address_space *,
+                                      unsigned long, unsigned long);
+void nilfs_forget_buffer(struct buffer_head *);
+void nilfs_copy_buffer(struct buffer_head *, struct buffer_head *);
+int nilfs_page_buffers_clean(struct page *);
+void nilfs_page_bug(struct page *);
+struct page *nilfs_alloc_private_page(struct block_device *, int,
+                                      unsigned long);
+void nilfs_free_private_page(struct page *);
+
+int nilfs_copy_dirty_pages(struct address_space *, struct address_space *);
+void nilfs_copy_back_pages(struct address_space *, struct address_space *);
+void nilfs_clear_dirty_pages(struct address_space *);
+unsigned nilfs_page_count_clean_buffers(struct page *, unsigned, unsigned);
+
+#define NILFS_PAGE_BUG(page, m, a...) \
+        do { nilfs_page_bug(page); BUG(); } while (0)
+
+static inline struct buffer_head *
+nilfs_page_get_nth_block(struct page *page, unsigned int count)
+{
+        struct buffer_head *bh = page_buffers(page);
+
+        while (count-- > 0)
+                bh = bh->b_this_page;
+        get_bh(bh);
+        return bh;
+}
+
+#endif /* _NILFS_PAGE_H */