BTRFS: Fix lseek return value for error

The recent reworking of btrfs' lseek lead to incorrect
values being returned.  This adds checks for seeking
beyond EOF in SEEK_HOLE and makes sure the error
values come back correct.

Andi Kleen also sent in similar patches.
Signed-off-by: NJie Liu <jeff.liu@oracle.com>
Reported-by: NAndi Kleen <ak@linux.intel.com>
Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/file.c

@@ -1817,6 +1817,11 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int origin)
 		goto out;
 	case SEEK_DATA:
 	case SEEK_HOLE:
+		if (offset >= i_size_read(inode)) {
+			mutex_unlock(&inode->i_mutex);
+			return -ENXIO;
+		}
+
 		ret = find_desired_extent(inode, &offset, origin);
 		if (ret) {
 			mutex_unlock(&inode->i_mutex);
@@ -1825,11 +1830,11 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int origin)
 	}
 
 	if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET)) {
-		ret = -EINVAL;
+		offset = -EINVAL;
 		goto out;
 	}
 	if (offset > inode->i_sb->s_maxbytes) {
-		ret = -EINVAL;
+		offset = -EINVAL;
 		goto out;
 	}