From 58ca80a77a4b82867922bc7c6ea0a26771a38135 Mon Sep 17 00:00:00 2001
From: Tim Crawford <tcrawford@datto.com>
Date: Dec 06 2018 14:13:54 +0000
Subject: Write the COW header after allocating the file


The header was being overwritten when fallocate was not supported,
causing backups to fail on the new agent. I would be interested to know
how it was working on newer kernels.

Resolves: #165

---

diff --git a/src/dattobd.c b/src/dattobd.c
index 2065182..e568661 100644
--- a/src/dattobd.c
+++ b/src/dattobd.c
@@ -2032,9 +2032,6 @@ static int cow_init(char *path, uint64_t elements, unsigned long sect_size, unsi
 	if(uuid) memcpy(cm->uuid, uuid, COW_UUID_SIZE);
 	else generate_random_uuid(cm->uuid);
 
-	ret = __cow_write_header_dirty(cm);
-	if(ret) goto error;
-
 	LOG_DEBUG("allocating cow manager array (%lu sections)", cm->total_sects);
 	cm->sects = kzalloc((cm->total_sects) * sizeof(struct cow_section), GFP_KERNEL | __GFP_NOWARN);
 	if(!cm->sects){
@@ -2052,6 +2049,9 @@ static int cow_init(char *path, uint64_t elements, unsigned long sect_size, unsi
 	ret = file_allocate(cm->filp, 0, file_max);
 	if(ret) goto error;
 
+	ret = __cow_write_header_dirty(cm);
+	if(ret) goto error;
+
 	*cm_out = cm;
 	return 0;