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Subject[patch 3/3] ext2: use perform_write aop
Date
Convert ext2 to use ->perform_write. This uses the main loop out of
generic_perform_write, but when encountering a short usercopy, it
zeroes out new uninitialised blocks, and passes in a short-length commit
to __block_commit_write, which does the right thing (in terms of not
setting things uptodate).

fs/buffer.c | 143 ++++++++++++++++++++++++++++++++++++++++++++
fs/ext2/inode.c | 7 ++
include/linux/buffer_head.h | 1
include/linux/pagemap.h | 2
4 files changed, 153 insertions(+)
Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -1866,6 +1866,50 @@ next_bh:
return err;
}

+void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
+{
+ unsigned int block_start, block_end;
+ struct buffer_head *head, *bh;
+
+ BUG_ON(!PageLocked(page));
+ if (!page_has_buffers(page))
+ return;
+
+ bh = head = page_buffers(page);
+ block_start = 0;
+ do {
+ block_end = block_start + bh->b_size;
+
+ if (buffer_new(bh)) {
+ if (block_end > from && block_start < to) {
+ if (!PageUptodate(page)) {
+ unsigned start, end;
+ void *kaddr;
+
+ start = max(from, block_start);
+ end = min(to, block_end);
+
+ kaddr = kmap_atomic(page, KM_USER0);
+ memset(kaddr+start, 0, block_end-end);
+ flush_dcache_page(page);
+ kunmap_atomic(kaddr, KM_USER0);
+ set_buffer_uptodate(bh);
+ }
+
+ /*
+ * XXX: make buffer_new behaviour more
+ * consistent.
+ * clear_buffer_new(bh);
+ */
+ mark_buffer_dirty(bh);
+ }
+ }
+
+ block_start = block_end;
+ bh = bh->b_this_page;
+ } while (bh != head);
+}
+
static int __block_commit_write(struct inode *inode, struct page *page,
unsigned from, unsigned to)
{
@@ -1900,6 +1944,105 @@ static int __block_commit_write(struct i
return 0;
}

+ssize_t block_perform_write(struct file *file, struct iovec_iterator *i,
+ loff_t pos, get_block_t *get_block)
+{
+ struct address_space *mapping = file->f_mapping;
+ struct inode *inode = mapping->host;
+ long status = 0;
+ ssize_t written = 0;
+
+ do {
+ struct page *page;
+ pgoff_t index; /* Pagecache index for current page */
+ unsigned long offset; /* Offset into pagecache page */
+ unsigned long bytes; /* Bytes to write to page */
+ size_t copied; /* Bytes copied from user */
+
+ offset = (pos & (PAGE_CACHE_SIZE - 1));
+ index = pos >> PAGE_CACHE_SHIFT;
+ bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
+ iovec_iterator_count(i));
+
+ /*
+ * Bring in the user page that we will copy from _first_.
+ * Otherwise there's a nasty deadlock on copying from the
+ * same page as we're writing to, without it being marked
+ * up-to-date.
+ *
+ * Not only is this an optimisation, but it is also required
+ * to check that the address is actually valid, when atomic
+ * usercopies are used, below.
+ */
+ if (unlikely(iovec_iterator_fault_in_readable(i))) {
+ status = -EFAULT;
+ break;
+ }
+
+ page = __grab_cache_page(mapping, index);
+ if (!page) {
+ status = -ENOMEM;
+ break;
+ }
+
+ status = __block_prepare_write(inode, page, offset,
+ offset+bytes, get_block);
+ if (unlikely(status)) {
+ ClearPageUptodate(page);
+
+ page_cache_release(page);
+
+ /*
+ * prepare_write() may have instantiated a few blocks
+ * outside i_size. Trim these off again. Don't need
+ * i_size_read because we hold i_mutex.
+ */
+ if (pos + bytes > inode->i_size)
+ vmtruncate(inode, inode->i_size);
+ break;
+ }
+
+ /*
+ * Must not enter the pagefault handler here, because
+ * we hold the page lock. See mm/filemap.c for more
+ * details.
+ */
+ pagefault_disable();
+ copied = iovec_iterator_copy_from_user_atomic(page, i,
+ offset, bytes);
+ pagefault_enable();
+ if (unlikely(copied < bytes))
+ page_zero_new_buffers(page, offset+copied, offset+bytes);
+ flush_dcache_page(page);
+
+ /* This could be a short (even 0-length) commit */
+ __block_commit_write(inode, page, offset, offset+copied);
+
+ unlock_page(page);
+ mark_page_accessed(page);
+ page_cache_release(page);
+
+ iovec_iterator_advance(i, copied);
+ pos += copied;
+ written += copied;
+
+ balance_dirty_pages_ratelimited(mapping);
+ cond_resched();
+
+ } while (iovec_iterator_count(i));
+
+ /*
+ * No need to use i_size_read() here, the i_size
+ * cannot change under us because we hold i_mutex.
+ */
+ if (pos > inode->i_size) {
+ i_size_write(inode, pos);
+ mark_inode_dirty(inode);
+ }
+
+ return written ? written : status;
+}
+
/*
* Generic "read page" function for block devices that have the normal
* get_block functionality. This is most of the block device filesystems.
Index: linux-2.6/fs/ext2/inode.c
===================================================================
--- linux-2.6.orig/fs/ext2/inode.c
+++ linux-2.6/fs/ext2/inode.c
@@ -642,6 +642,12 @@ ext2_readpages(struct file *file, struct
return mpage_readpages(mapping, pages, nr_pages, ext2_get_block);
}

+static ssize_t
+ext2_perform_write(struct file *file, struct iovec_iterator *i, loff_t pos)
+{
+ return block_perform_write(file, i, pos, ext2_get_block);
+}
+
static int
ext2_prepare_write(struct file *file, struct page *page,
unsigned from, unsigned to)
@@ -689,6 +695,7 @@ const struct address_space_operations ex
.readpages = ext2_readpages,
.writepage = ext2_writepage,
.sync_page = block_sync_page,
+ .perform_write = ext2_perform_write,
.prepare_write = ext2_prepare_write,
.commit_write = generic_commit_write,
.bmap = ext2_bmap,
Index: linux-2.6/include/linux/buffer_head.h
===================================================================
--- linux-2.6.orig/include/linux/buffer_head.h
+++ linux-2.6/include/linux/buffer_head.h
@@ -198,6 +198,7 @@ void block_invalidatepage(struct page *p
int block_write_full_page(struct page *page, get_block_t *get_block,
struct writeback_control *wbc);
int block_read_full_page(struct page*, get_block_t*);
+ssize_t block_perform_write(struct file *, struct iovec_iterator*, loff_t, get_block_t*);
int block_prepare_write(struct page*, unsigned, unsigned, get_block_t*);
int cont_prepare_write(struct page*, unsigned, unsigned, get_block_t*,
loff_t *);
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h
+++ linux-2.6/include/linux/pagemap.h
@@ -87,6 +87,8 @@ unsigned find_get_pages_contig(struct ad
unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
int tag, unsigned int nr_pages, struct page **pages);

+struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index);
+
/*
* Returns locked page at given index in given cache, creating it if needed.
*/
-
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