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authorDavid Chinner <dgc@sgi.com>2007-07-19 17:39:55 +1000
committerTim Shimmin <tes@chook.melbourne.sgi.com>2007-07-19 19:50:50 +1000
commit5417169026c3df151adf5a65eb061278b0a72e69 (patch)
treee4872a4243e12fe931ff6ac789df181b579b884c /fs/buffer.c
parent589f1e81bde732dd0b1bc5d01b6bddd4bcb4527b (diff)
[FS] Implement block_page_mkwrite.
Many filesystems need a ->page-mkwrite callout to correctly set up pages that have been written to by mmap. This is especially important when mmap is writing into holes as it allows filesystems to correctly account for and allocate space before the mmap write is allowed to proceed. Protection against truncate races is provided by locking the page and checking to see whether the page mapping is correct and whether it is beyond EOF so we don't end up allowing allocations beyond the current EOF or changing EOF as a result of a mmap write. SGI-PV: 940392 SGI-Modid: 2.6.x-xfs-melb:linux:29146a Signed-off-by: David Chinner <dgc@sgi.com> Signed-off-by: Christoph Hellwig <hch@infradead.org> Signed-off-by: Tim Shimmin <tes@sgi.com>
Diffstat (limited to 'fs/buffer.c')
-rw-r--r--fs/buffer.c47
1 files changed, 47 insertions, 0 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index 0f9006714230..02ebb1f1d3b0 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2194,6 +2194,52 @@ int generic_commit_write(struct file *file, struct page *page,
return 0;
}
+/*
+ * block_page_mkwrite() is not allowed to change the file size as it gets
+ * called from a page fault handler when a page is first dirtied. Hence we must
+ * be careful to check for EOF conditions here. We set the page up correctly
+ * for a written page which means we get ENOSPC checking when writing into
+ * holes and correct delalloc and unwritten extent mapping on filesystems that
+ * support these features.
+ *
+ * We are not allowed to take the i_mutex here so we have to play games to
+ * protect against truncate races as the page could now be beyond EOF. Because
+ * vmtruncate() writes the inode size before removing pages, once we have the
+ * page lock we can determine safely if the page is beyond EOF. If it is not
+ * beyond EOF, then the page is guaranteed safe against truncation until we
+ * unlock the page.
+ */
+int
+block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
+ get_block_t get_block)
+{
+ struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
+ unsigned long end;
+ loff_t size;
+ int ret = -EINVAL;
+
+ lock_page(page);
+ size = i_size_read(inode);
+ if ((page->mapping != inode->i_mapping) ||
+ ((page->index << PAGE_CACHE_SHIFT) > size)) {
+ /* page got truncated out from underneath us */
+ goto out_unlock;
+ }
+
+ /* page is wholly or partially inside EOF */
+ if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
+ end = size & ~PAGE_CACHE_MASK;
+ else
+ end = PAGE_CACHE_SIZE;
+
+ ret = block_prepare_write(page, 0, end, get_block);
+ if (!ret)
+ ret = block_commit_write(page, 0, end);
+
+out_unlock:
+ unlock_page(page);
+ return ret;
+}
/*
* nobh_prepare_write()'s prereads are special: the buffer_heads are freed
@@ -2977,6 +3023,7 @@ EXPORT_SYMBOL(__brelse);
EXPORT_SYMBOL(__wait_on_buffer);
EXPORT_SYMBOL(block_commit_write);
EXPORT_SYMBOL(block_prepare_write);
+EXPORT_SYMBOL(block_page_mkwrite);
EXPORT_SYMBOL(block_read_full_page);
EXPORT_SYMBOL(block_sync_page);
EXPORT_SYMBOL(block_truncate_page);