[PATCH 11/30] Unionfs: restructure unionfs_setattr and fix truncation order

[Erez Zadok <ezk@cs.sunysb.edu>]

From: Hugh Dickins <hugh@veritas.com>

Restructure the code to move the lower notify_change out of the loop in
unionfs_setattr.  Cleanup and simplify the code.  Then fix the truncation
order which fsx-linux in a unionfs on tmpfs found.  Then handle copyup
properly.

When shrinking a file, unionfs_setattr needs to vmtruncate the upper level
before notifying change to the lower level, to eliminate those dirty pages
beyond new eof which otherwise drift down to the lower level's writepage,
writing beyond its eof (and later uncovered when the file is expanded).

Also truncate the upper level first when expanding, in the case when
the upper level's s_maxbytes is more limiting than the lower level's.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
---
 fs/unionfs/inode.c |   97 ++++++++++++++++++++++++++-------------------------
 1 files changed, 49 insertions(+), 48 deletions(-)

diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
index 78cdfa2..37258c8 100644
--- a/fs/unionfs/inode.c
+++ b/fs/unionfs/inode.c
@@ -998,11 +998,10 @@ static int unionfs_setattr(struct dentry *dentry, struct iattr *ia)
 {
 	int err = 0;
 	struct dentry *lower_dentry;
-	struct inode *inode = NULL;
-	struct inode *lower_inode = NULL;
+	struct inode *inode;
+	struct inode *lower_inode;
 	int bstart, bend, bindex;
-	int i;
-	int copyup = 0;
+	loff_t size;
 
 	unionfs_read_lock(dentry->d_sb);
 	unionfs_lock_dentry(dentry);
@@ -1023,62 +1022,64 @@ static int unionfs_setattr(struct dentry *dentry, struct iattr *ia)
 	if (ia->ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID))
 		ia->ia_valid &= ~ATTR_MODE;
 
-	for (bindex = bstart; (bindex <= bend) || (bindex == bstart);
-	     bindex++) {
-		lower_dentry = unionfs_lower_dentry_idx(dentry, bindex);
-		if (!lower_dentry)
-			continue;
-		BUG_ON(lower_dentry->d_inode == NULL);
-
-		/* If the file is on a read only branch */
-		if (is_robranch_super(dentry->d_sb, bindex)
-		    || IS_RDONLY(lower_dentry->d_inode)) {
-			if (copyup || (bindex != bstart))
-				continue;
-			/* Only if its the leftmost file, copyup the file */
-			for (i = bstart - 1; i >= 0; i--) {
-				loff_t size = i_size_read(dentry->d_inode);
-				if (ia->ia_valid & ATTR_SIZE)
-					size = ia->ia_size;
-				err = copyup_dentry(dentry->d_parent->d_inode,
-						    dentry, bstart, i,
-						    dentry->d_name.name,
-						    dentry->d_name.len,
-						    NULL, size);
-
-				if (!err) {
-					copyup = 1;
-					lower_dentry =
-						unionfs_lower_dentry(dentry);
-					break;
-				}
-				/*
-				 * if error is in the leftmost branch, pass
-				 * it up.
-				 */
-				if (i == 0)
-					goto out;
-			}
+	lower_dentry = unionfs_lower_dentry(dentry);
+	BUG_ON(!lower_dentry);	/* should never happen after above revalidate */
+
+	/* copyup if the file is on a read only branch */
+	if (is_robranch_super(dentry->d_sb, bstart)
+	    || IS_RDONLY(lower_dentry->d_inode)) {
+		/* check if we have a branch to copy up to */
+		if (bstart <= 0) {
+			err = -EACCES;
+			goto out;
+		}
 
+		if (ia->ia_valid & ATTR_SIZE)
+			size = ia->ia_size;
+		else
+			size = i_size_read(inode);
+		/* copyup to next available branch */
+		for (bindex = bstart - 1; bindex >= 0; bindex--) {
+			err = copyup_dentry(dentry->d_parent->d_inode,
+					    dentry, bstart, bindex,
+					    dentry->d_name.name,
+					    dentry->d_name.len,
+					    NULL, size);
+			if (!err)
+				break;
 		}
-		err = notify_change(lower_dentry, ia);
 		if (err)
 			goto out;
-		break;
+		/* get updated lower_dentry after copyup */
+		lower_dentry = unionfs_lower_dentry(dentry);
 	}
 
-	/* for mmap */
+	lower_inode = unionfs_lower_inode(inode);
+
+	/*
+	 * If shrinking, first truncate upper level to cancel writing dirty
+	 * pages beyond the new eof; and also if its' maxbytes is more
+	 * limiting (fail with -EFBIG before making any change to the lower
+	 * level).  There is no need to vmtruncate the upper level
+	 * afterwards in the other cases: we fsstack_copy_inode_size from
+	 * the lower level.
+	 */
 	if (ia->ia_valid & ATTR_SIZE) {
-		if (ia->ia_size != i_size_read(inode)) {
+		size = i_size_read(inode);
+		if (ia->ia_size < size || (ia->ia_size > size &&
+		    inode->i_sb->s_maxbytes < lower_inode->i_sb->s_maxbytes)) {
 			err = vmtruncate(inode, ia->ia_size);
 			if (err)
-				printk(KERN_ERR
-				       "unionfs: setattr: vmtruncate failed\n");
+				goto out;
 		}
 	}
 
-	/* get the size from the first lower inode */
-	lower_inode = unionfs_lower_inode(inode);
+	/* notify the (possibly copied-up) lower inode */
+	err = notify_change(lower_dentry, ia);
+	if (err)
+		goto out;
+
+	/* get attributes from the first lower inode */
 	unionfs_copy_attr_all(inode, lower_inode);
 	/*
 	 * unionfs_copy_attr_all will copy the lower times to our inode if
-- 
1.5.2.2