[RFC PATCH v3 1/3] nvdimm: set force_raw=1 in kdump kernel

[Li Zhijian]

The virtually mapped memory map allows storing struct page objects for
persistent memory devices in pre-allocated storage on those devices.
These 'struct page objects' on devices are also known as metadata.

During libnvdimm/nd_pmem are loading, the previous metadata will
be re-constructed to fit the current running kernel. For kdump purpose,
these metadata should not be touched until the dumping is done so that
the metadata is identical.

To achieve this, we have some options
1. Don't provide libnvdimm driver in kdump kernel rootfs/initramfs
2. Disable libnvdimm driver by specific comline parameters (
   initcall_blacklist=libnvdimm_init libnvdimm.blacklist=1 rd.driver.blacklist=libnvdimm)
3. Enforce force_raw=1 for nvdimm namespace, because when force_raw=1,
   metadata will not be re-constructed again. This may also result in
   the pmem doesn't work before a few extra configurations.

Here we choose the 3rd one because the kdump application in this RFC relies
on some /sys interfaces exported by libnvdimm and nd_pmem etc.

CC: Dan Williams <dan.j.williams@xxxxxxxxx>
CC: Vishal Verma <vishal.l.verma@xxxxxxxxx>
CC: Dave Jiang <dave.jiang@xxxxxxxxx>
CC: Ira Weiny <ira.weiny@xxxxxxxxx>
CC: nvdimm@xxxxxxxxxxxxxxx
Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
---
V3: new patch
---
 drivers/nvdimm/namespace_devs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/nvdimm/namespace_devs.c b/drivers/nvdimm/namespace_devs.c
index c60ec0b373c5..2e59be8b9c78 100644
--- a/drivers/nvdimm/namespace_devs.c
+++ b/drivers/nvdimm/namespace_devs.c
@@ -8,6 +8,7 @@
 #include <linux/slab.h>
 #include <linux/list.h>
 #include <linux/nd.h>
+#include <linux/crash_dump.h>
 #include "nd-core.h"
 #include "pmem.h"
 #include "pfn.h"
@@ -1504,6 +1505,8 @@ struct nd_namespace_common *nvdimm_namespace_common_probe(struct device *dev)
 			return ERR_PTR(-ENODEV);
 	}
 
+	if (is_kdump_kernel())
+		ndns->force_raw = true;
 	return ndns;
 }
 EXPORT_SYMBOL(nvdimm_namespace_common_probe);
-- 
2.29.2