ovl: Open file with data except for the case of fsync

ovl_open() should open file which contains data and not open metacopy
inode.  With the introduction of metacopy inodes, with current
implementaion we will end up opening metacopy inode as well.

But there can be certain circumstances like ovl_fsync() where we want to
allow opening a metacopy inode instead.

Hence, change ovl_open_realfile() and and add extra parameter which
specifies whether to allow opening metacopy inode or not.  If this
parameter is false, we look for data inode and open that.

This should allow covering both the cases.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Reviewed-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/file.c

@@ -13,11 +13,20 @@
 #include <linux/uio.h>
 #include "overlayfs.h"
 
-static struct file *ovl_open_realfile(const struct file *file)
+static char ovl_whatisit(struct inode *inode, struct inode *realinode)
+{
+	if (realinode != ovl_inode_upper(inode))
+		return 'l';
+	if (ovl_has_upperdata(inode))
+		return 'u';
+	else
+		return 'm';
+}
+
+static struct file *ovl_open_realfile(const struct file *file,
+				      struct inode *realinode)
 {
 	struct inode *inode = file_inode(file);
-	struct inode *upperinode = ovl_inode_upper(inode);
-	struct inode *realinode = upperinode ?: ovl_inode_lower(inode);
 	struct file *realfile;
 	const struct cred *old_cred;
 
@@ -27,7 +36,7 @@ static struct file *ovl_open_realfile(const struct file *file)
 	revert_creds(old_cred);
 
 	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
-		 file, file, upperinode ? 'u' : 'l', file->f_flags,
+		 file, file, ovl_whatisit(inode, realinode), file->f_flags,
 		 realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
 
 	return realfile;
@@ -71,17 +80,24 @@ static int ovl_change_flags(struct file *file, unsigned int flags)
 	return 0;
 }
 
-static int ovl_real_fdget(const struct file *file, struct fd *real)
+static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
+			       bool allow_meta)
 {
 	struct inode *inode = file_inode(file);
+	struct inode *realinode;
 
 	real->flags = 0;
 	real->file = file->private_data;
 
+	if (allow_meta)
+		realinode = ovl_inode_real(inode);
+	else
+		realinode = ovl_inode_realdata(inode);
+
 	/* Has it been copied up since we'd opened it? */
-	if (unlikely(file_inode(real->file) != ovl_inode_real(inode))) {
+	if (unlikely(file_inode(real->file) != realinode)) {
 		real->flags = FDPUT_FPUT;
-		real->file = ovl_open_realfile(file);
+		real->file = ovl_open_realfile(file, realinode);
 
 		return PTR_ERR_OR_ZERO(real->file);
 	}
@@ -93,6 +109,11 @@ static int ovl_real_fdget(const struct file *file, struct fd *real)
 	return 0;
 }
 
+static int ovl_real_fdget(const struct file *file, struct fd *real)
+{
+	return ovl_real_fdget_meta(file, real, false);
+}
+
 static int ovl_open(struct inode *inode, struct file *file)
 {
 	struct dentry *dentry = file_dentry(file);
@@ -106,7 +127,7 @@ static int ovl_open(struct inode *inode, struct file *file)
 	/* No longer need these flags, so don't pass them on to underlying fs */
 	file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 
-	realfile = ovl_open_realfile(file);
+	realfile = ovl_open_realfile(file, ovl_inode_realdata(inode));
 	if (IS_ERR(realfile))
 		return PTR_ERR(realfile);
 
@@ -243,7 +264,7 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	const struct cred *old_cred;
 	int ret;
 
-	ret = ovl_real_fdget(file, &real);
+	ret = ovl_real_fdget_meta(file, &real, !datasync);
 	if (ret)
 		return ret;