[PATCH v3 4/5] ext4: disable map_sync for virtio pmem

[Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Virtio pmem provides asynchronous host page cache flush
mechanism. We don't support 'MAP_SYNC' with virtio pmem 
and ext4. 

Signed-off-by: Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 fs/ext4/file.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 69d65d4..e54f48b 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -360,8 +360,10 @@ static const struct vm_operations_struct ext4_file_vm_ops = {
 static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct inode *inode = file->f_mapping->host;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	struct dax_device *dax_dev = sbi->s_daxdev;
 
-	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
+	if (unlikely(ext4_forced_shutdown(sbi)))
 		return -EIO;
 
 	/*
@@ -371,6 +373,13 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!IS_DAX(file_inode(file)) && (vma->vm_flags & VM_SYNC))
 		return -EOPNOTSUPP;
 
+	/* We don't support synchronous mappings with guest direct access
+	 * and virtio based host page cache flush mechanism.
+	 */
+	if (IS_DAX(file_inode(file)) && virtio_pmem_host_cache_enabled(dax_dev)
+						&& (vma->vm_flags & VM_SYNC))
+		return -EOPNOTSUPP;
+
 	file_accessed(file);
 	if (IS_DAX(file_inode(file))) {
 		vma->vm_ops = &ext4_dax_vm_ops;
-- 
2.9.3