fuse: move reverting attributes to fuse_change_attributes()

In case of writeback_cache fuse_fillattr() would revert the queried
attributes to the cached version.

Move this to fuse_change_attributes() in order to manage the writeback
logic in a central helper.  This will be necessary for patches that follow.

Only fuse_do_getattr() -> fuse_fillattr() uses the attributes after calling
fuse_change_attributes(), so this should not change behavior.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dir.c

@@ -944,15 +944,6 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
 	unsigned int blkbits;
 	struct fuse_conn *fc = get_fuse_conn(inode);
 
-	/* see the comment in fuse_change_attributes() */
-	if (fc->writeback_cache && S_ISREG(inode->i_mode)) {
-		attr->size = i_size_read(inode);
-		attr->mtime = inode->i_mtime.tv_sec;
-		attr->mtimensec = inode->i_mtime.tv_nsec;
-		attr->ctime = inode->i_ctime.tv_sec;
-		attr->ctimensec = inode->i_ctime.tv_nsec;
-	}
-
 	stat->dev = inode->i_sb->s_dev;
 	stat->ino = attr->ino;
 	stat->mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);

fs/fuse/inode.c

@@ -228,6 +228,19 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 	struct timespec64 old_mtime;
 
 	spin_lock(&fi->lock);
+	/*
+	 * In case of writeback_cache enabled, writes update mtime, ctime and
+	 * may update i_size.  In these cases trust the cached value in the
+	 * inode.
+	 */
+	if (is_wb) {
+		attr->size = i_size_read(inode);
+		attr->mtime = inode->i_mtime.tv_sec;
+		attr->mtimensec = inode->i_mtime.tv_nsec;
+		attr->ctime = inode->i_ctime.tv_sec;
+		attr->ctimensec = inode->i_ctime.tv_nsec;
+	}
+
 	if ((attr_version != 0 && fi->attr_version > attr_version) ||
 	    test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
 		spin_unlock(&fi->lock);