fs: restore nobh

Implement nobh in new aops.  This is a bit tricky.  FWIW, nobh_truncate is
now implemented in a way that does not create blocks in sparse regions,
which is a silly thing for it to have been doing (isn't it?)

ext2 survives fsx and fsstress. jfs is converted as well... ext3
should be easy to do (but not done yet).

[akpm@linux-foundation.org: coding-style fixes]
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 171 insertions, 85 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index a89d25bf1171..a406cfd89e3b 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2369,7 +2369,7 @@ out_unlock:
 }
 
 /*
- * nobh_prepare_write()'s prereads are special: the buffer_heads are freed
+ * nobh_write_begin()'s prereads are special: the buffer_heads are freed
  * immediately, while under the page lock.  So it needs a special end_io
  * handler which does not touch the bh after unlocking it.
  */
@@ -2379,16 +2379,45 @@ static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
 }
 
 /*
+ * Attach the singly-linked list of buffers created by nobh_write_begin, to
+ * the page (converting it to circular linked list and taking care of page
+ * dirty races).
+ */
+static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
+{
+        struct buffer_head *bh;
+
+        BUG_ON(!PageLocked(page));
+
+        spin_lock(&page->mapping->private_lock);
+        bh = head;
+        do {
+                if (PageDirty(page))
+                        set_buffer_dirty(bh);
+                if (!bh->b_this_page)
+                        bh->b_this_page = head;
+                bh = bh->b_this_page;
+        } while (bh != head);
+        attach_page_buffers(page, head);
+        spin_unlock(&page->mapping->private_lock);
+}
+
+/*
  * On entry, the page is fully not uptodate.
  * On exit the page is fully uptodate in the areas outside (from,to)
  */
-int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
+int nobh_write_begin(struct file *file, struct address_space *mapping,
+                        loff_t pos, unsigned len, unsigned flags,
+                        struct page **pagep, void **fsdata,
                         get_block_t *get_block)
 {
-        struct inode *inode = page->mapping->host;
+        struct inode *inode = mapping->host;
         const unsigned blkbits = inode->i_blkbits;
         const unsigned blocksize = 1 << blkbits;
         struct buffer_head *head, *bh;
+        struct page *page;
+        pgoff_t index;
+        unsigned from, to;
         unsigned block_in_page;
         unsigned block_start, block_end;
         sector_t block_in_file;
@@ -2397,8 +2426,23 @@ int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
         int ret = 0;
         int is_mapped_to_disk = 1;
 
-        if (page_has_buffers(page))
-                return block_prepare_write(page, from, to, get_block);
+        index = pos >> PAGE_CACHE_SHIFT;
+        from = pos & (PAGE_CACHE_SIZE - 1);
+        to = from + len;
+
+        page = __grab_cache_page(mapping, index);
+        if (!page)
+                return -ENOMEM;
+        *pagep = page;
+        *fsdata = NULL;
+
+        if (page_has_buffers(page)) {
+                unlock_page(page);
+                page_cache_release(page);
+                *pagep = NULL;
+                return block_write_begin(file, mapping, pos, len, flags, pagep,
+                                        fsdata, get_block);
+        }
 
         if (PageMappedToDisk(page))
                 return 0;
@@ -2413,8 +2457,10 @@ int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
          * than the circular one we're used to.
          */
         head = alloc_page_buffers(page, blocksize, 0);
-        if (!head)
-                return -ENOMEM;
+        if (!head) {
+                ret = -ENOMEM;
+                goto out_release;
+        }
 
         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 
@@ -2483,15 +2529,12 @@ int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
         if (is_mapped_to_disk)
                 SetPageMappedToDisk(page);
 
-        do {
-                bh = head;
-                head = head->b_this_page;
-                free_buffer_head(bh);
-        } while (head);
+        *fsdata = head; /* to be released by nobh_write_end */
 
         return 0;
 
 failed:
+        BUG_ON(!ret);
         /*
          * Error recovery is a bit difficult. We need to zero out blocks that
          * were newly allocated, and dirty them to ensure they get written out.
@@ -2499,64 +2542,57 @@ failed:
          * the handling of potential IO errors during writeout would be hard
          * (could try doing synchronous writeout, but what if that fails too?)
          */
-        spin_lock(&page->mapping->private_lock);
-        bh = head;
-        block_start = 0;
-        do {
-                if (PageUptodate(page))
-                        set_buffer_uptodate(bh);
-                if (PageDirty(page))
-                        set_buffer_dirty(bh);
+        attach_nobh_buffers(page, head);
+        page_zero_new_buffers(page, from, to);
 
-                block_end = block_start+blocksize;
-                if (block_end <= from)
-                        goto next;
-                if (block_start >= to)
-                        goto next;
+out_release:
+        unlock_page(page);
+        page_cache_release(page);
+        *pagep = NULL;
 
-                if (buffer_new(bh)) {
-                        clear_buffer_new(bh);
-                        if (!buffer_uptodate(bh)) {
-                                zero_user_page(page, block_start, bh->b_size, KM_USER0);
-                                set_buffer_uptodate(bh);
-                        }
-                        mark_buffer_dirty(bh);
-                }
-next:
-                block_start = block_end;
-                if (!bh->b_this_page)
-                        bh->b_this_page = head;
-                bh = bh->b_this_page;
-        } while (bh != head);
-        attach_page_buffers(page, head);
-        spin_unlock(&page->mapping->private_lock);
+        if (pos + len > inode->i_size)
+                vmtruncate(inode, inode->i_size);
 
         return ret;
 }
-EXPORT_SYMBOL(nobh_prepare_write);
+EXPORT_SYMBOL(nobh_write_begin);
 
-/*
- * Make sure any changes to nobh_commit_write() are reflected in
- * nobh_truncate_page(), since it doesn't call commit_write().
- */
-int nobh_commit_write(struct file *file, struct page *page,
-                unsigned from, unsigned to)
+int nobh_write_end(struct file *file, struct address_space *mapping,
+                        loff_t pos, unsigned len, unsigned copied,
+                        struct page *page, void *fsdata)
 {
         struct inode *inode = page->mapping->host;
-        loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+        struct buffer_head *head = NULL;
+        struct buffer_head *bh;
 
-        if (page_has_buffers(page))
-                return generic_commit_write(file, page, from, to);
+        if (!PageMappedToDisk(page)) {
+                if (unlikely(copied < len) && !page_has_buffers(page))
+                        attach_nobh_buffers(page, head);
+                if (page_has_buffers(page))
+                        return generic_write_end(file, mapping, pos, len,
+                                                copied, page, fsdata);
+        }
 
         SetPageUptodate(page);
         set_page_dirty(page);
-        if (pos > inode->i_size) {
-                i_size_write(inode, pos);
+        if (pos+copied > inode->i_size) {
+                i_size_write(inode, pos+copied);
                 mark_inode_dirty(inode);
         }
-        return 0;
+
+        unlock_page(page);
+        page_cache_release(page);
+
+        head = fsdata;
+        while (head) {
+                bh = head;
+                head = head->b_this_page;
+                free_buffer_head(bh);
+        }
+
+        return copied;
 }
-EXPORT_SYMBOL(nobh_commit_write);
+EXPORT_SYMBOL(nobh_write_end);
 
 /*
  * nobh_writepage() - based on block_full_write_page() except
@@ -2609,44 +2645,79 @@ out:
 }
 EXPORT_SYMBOL(nobh_writepage);
 
-/*
- * This function assumes that ->prepare_write() uses nobh_prepare_write().
- */
-int nobh_truncate_page(struct address_space *mapping, loff_t from)
+int nobh_truncate_page(struct address_space *mapping,
+                        loff_t from, get_block_t *get_block)
 {
-        struct inode *inode = mapping->host;
-        unsigned blocksize = 1 << inode->i_blkbits;
         pgoff_t index = from >> PAGE_CACHE_SHIFT;
         unsigned offset = from & (PAGE_CACHE_SIZE-1);
-        unsigned to;
+        unsigned blocksize;
+        sector_t iblock;
+        unsigned length, pos;
+        struct inode *inode = mapping->host;
         struct page *page;
-        const struct address_space_operations *a_ops = mapping->a_ops;
-        int ret = 0;
+        struct buffer_head map_bh;
+        int err;
 
-        if ((offset & (blocksize - 1)) == 0)
-                goto out;
+        blocksize = 1 << inode->i_blkbits;
+        length = offset & (blocksize - 1);
+
+        /* Block boundary? Nothing to do */
+        if (!length)
+                return 0;
+
+        length = blocksize - length;
+        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
 
-        ret = -ENOMEM;
         page = grab_cache_page(mapping, index);
+        err = -ENOMEM;
         if (!page)
                 goto out;
 
-        to = (offset + blocksize) & ~(blocksize - 1);
-        ret = a_ops->prepare_write(NULL, page, offset, to);
-        if (ret == 0) {
-                zero_user_page(page, offset, PAGE_CACHE_SIZE - offset,
-                                KM_USER0);
-                /*
-                 * It would be more correct to call aops->commit_write()
-                 * here, but this is more efficient.
-                 */
-                SetPageUptodate(page);
-                set_page_dirty(page);
+        if (page_has_buffers(page)) {
+has_buffers:
+                unlock_page(page);
+                page_cache_release(page);
+                return block_truncate_page(mapping, from, get_block);
         }
+
+        /* Find the buffer that contains "offset" */
+        pos = blocksize;
+        while (offset >= pos) {
+                iblock++;
+                pos += blocksize;
+        }
+
+        err = get_block(inode, iblock, &map_bh, 0);
+        if (err)
+                goto unlock;
+        /* unmapped? It's a hole - nothing to do */
+        if (!buffer_mapped(&map_bh))
+                goto unlock;
+
+        /* Ok, it's mapped. Make sure it's up-to-date */
+        if (!PageUptodate(page)) {
+                err = mapping->a_ops->readpage(NULL, page);
+                if (err) {
+                        page_cache_release(page);
+                        goto out;
+                }
+                lock_page(page);
+                if (!PageUptodate(page)) {
+                        err = -EIO;
+                        goto unlock;
+                }
+                if (page_has_buffers(page))
+                        goto has_buffers;
+        }
+        zero_user_page(page, offset, length, KM_USER0);
+        set_page_dirty(page);
+        err = 0;
+
+unlock:
         unlock_page(page);
         page_cache_release(page);
 out:
-        return ret;
+        return err;
 }
 EXPORT_SYMBOL(nobh_truncate_page);
 
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 63ab02aa4c52..1b102a1ccebb 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -659,6 +659,20 @@ ext2_write_begin(struct file *file, struct address_space *mapping,
         return __ext2_write_begin(file, mapping, pos, len, flags, pagep,fsdata);
 }
 
+static int
+ext2_nobh_write_begin(struct file *file, struct address_space *mapping,
+                loff_t pos, unsigned len, unsigned flags,
+                struct page **pagep, void **fsdata)
+{
+        /*
+         * Dir-in-pagecache still uses ext2_write_begin. Would have to rework
+         * directory handling code to pass around offsets rather than struct
+         * pages in order to make this work easily.
+         */
+        return nobh_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
+                                                        ext2_get_block);
+}
+
 static int ext2_nobh_writepage(struct page *page,
                         struct writeback_control *wbc)
 {
@@ -710,7 +724,8 @@ const struct address_space_operations ext2_nobh_aops = {
         .readpages              = ext2_readpages,
         .writepage              = ext2_nobh_writepage,
         .sync_page              = block_sync_page,
-        /* XXX: todo */
+        .write_begin            = ext2_nobh_write_begin,
+        .write_end              = nobh_write_end,
         .bmap                   = ext2_bmap,
         .direct_IO              = ext2_direct_IO,
         .writepages             = ext2_writepages,
@@ -927,7 +942,8 @@ void ext2_truncate (struct inode * inode)
         if (mapping_is_xip(inode->i_mapping))
                 xip_truncate_page(inode->i_mapping, inode->i_size);
         else if (test_opt(inode->i_sb, NOBH))
-                nobh_truncate_page(inode->i_mapping, inode->i_size);
+                nobh_truncate_page(inode->i_mapping,
+                                inode->i_size, ext2_get_block);
         else
                 block_truncate_page(inode->i_mapping,
                                 inode->i_size, ext2_get_block);
diff --git a/fs/jfs/inode.c b/fs/jfs/inode.c
index 6af378563611..4672013802e1 100644
--- a/fs/jfs/inode.c
+++ b/fs/jfs/inode.c
@@ -279,8 +279,7 @@ static int jfs_write_begin(struct file *file, struct address_space *mapping,
                                 loff_t pos, unsigned len, unsigned flags,
                                 struct page **pagep, void **fsdata)
 {
-        *pagep = NULL;
-        return block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
+        return nobh_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                                 jfs_get_block);
 }
 
@@ -306,7 +305,7 @@ const struct address_space_operations jfs_aops = {
         .writepages     = jfs_writepages,
         .sync_page      = block_sync_page,
         .write_begin    = jfs_write_begin,
-        .write_end      = generic_write_end,
+        .write_end      = nobh_write_end,
         .bmap           = jfs_bmap,
         .direct_IO      = jfs_direct_IO,
 };
@@ -359,7 +358,7 @@ void jfs_truncate(struct inode *ip)
 {
         jfs_info("jfs_truncate: size = 0x%lx", (ulong) ip->i_size);
 
-        block_truncate_page(ip->i_mapping, ip->i_size, jfs_get_block);
+        nobh_truncate_page(ip->i_mapping, ip->i_size, jfs_get_block);
 
         IWRITE_LOCK(ip, RDWRLOCK_NORMAL);
         jfs_truncate_nolock(ip, ip->i_size);