From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: [RFC][PATCH] ext4: Use page_mkwrite vma_operations to get mmap write notification.
Date: Thu, 28 Feb 2008 23:35:08 +0530
Message-ID: <1204221911-9753-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Cc: linux-ext4@vger.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: cmm@us.ibm.com
Sender: linux-ext4-owner@vger.kernel.org

We would like to get notified when we are doing a write on mmap section.
This is needed with respect to preallocated area. We split the preallocated
area into initialzed extent and uninitialzed extent in the call back. This
let us handle ENOSPC better. Otherwise we get ENOSPC in the writepage and
that would result in data loss. The changes are also needed to handle ENOSPC
when writing to an mmap section of files with holes.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 fs/ext4/file.c          |   19 +++++++++++++++-
 fs/ext4/inode.c         |   54 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/ext4_fs.h |    1 +
 3 files changed, 73 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 20507a2..77341c1 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -123,6 +123,23 @@ force_commit:
 	return ret;
 }
 
+static struct vm_operations_struct ext4_file_vm_ops = {
+	.fault		= filemap_fault,
+	.page_mkwrite   = ext4_page_mkwrite,
+};
+
+static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	if (!mapping->a_ops->readpage)
+		return -ENOEXEC;
+	file_accessed(file);
+	vma->vm_ops = &ext4_file_vm_ops;
+	vma->vm_flags |= VM_CAN_NONLINEAR;
+	return 0;
+}
+
 const struct file_operations ext4_file_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= do_sync_read,
@@ -133,7 +150,7 @@ const struct file_operations ext4_file_operations = {
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ext4_compat_ioctl,
 #endif
-	.mmap		= generic_file_mmap,
+	.mmap		= ext4_file_mmap,
 	.open		= generic_file_open,
 	.release	= ext4_release_file,
 	.fsync		= ext4_sync_file,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 5b5d63d..62aafc3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3490,3 +3490,57 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
 
 	return err;
 }
+
+int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+{
+	unsigned long end;
+	loff_t size;
+	handle_t *handle;
+	int ret = -EINVAL, needed_blocks;
+	struct file *file   = vma->vm_file;
+	struct inode *inode = file->f_path.dentry->d_inode;
+
+	needed_blocks = ext4_writepage_trans_blocks(inode);
+	/* We need to take inode mutex to prevent parallel write */
+	mutex_lock(&inode->i_mutex);
+	lock_page(page);
+	size = i_size_read(inode);
+	if ((page->mapping != inode->i_mapping) ||
+	    (page_offset(page) > 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;
+
+	/*
+	 * if ext4_get_block resulted in a split of an uninitialized extent,
+	 * in file system full case, we will have to take the journal write
+	 * access and zero out the page.
+	 */
+	handle = ext4_journal_start(inode, needed_blocks);
+	if (IS_ERR(handle)) {
+		ret = PTR_ERR(handle);
+		goto out_unlock;
+	}
+	/* Will zero out the pages if buffer is marked new */
+	ret = block_prepare_write(page, 0, end, ext4_get_block);
+
+	/*
+	 * Now call commit_write to mark the buffer dirty and page
+	 * uptodate. page_mkwrite makes the page dirty towards the
+	 * end. We don't want to mark the buffer dirty for
+	 * journalled mode.
+	 */
+	 if (!ext4_should_journal_data(inode))
+		 ret = block_commit_write(page, 0, end);
+
+	ext4_journal_stop(handle);
+out_unlock:
+	unlock_page(page);
+	mutex_unlock(&inode->i_mutex);
+	return ret;
+}
diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
index 22810b1..8f5a563 100644
--- a/include/linux/ext4_fs.h
+++ b/include/linux/ext4_fs.h
@@ -1059,6 +1059,7 @@ extern void ext4_set_aops(struct inode *inode);
 extern int ext4_writepage_trans_blocks(struct inode *);
 extern int ext4_block_truncate_page(handle_t *handle, struct page *page,
 		struct address_space *mapping, loff_t from);
+extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
 
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
-- 
1.5.4.3.325.g6d216.dirty