[PATCH RFC 05/13] mm: PRAM: link nodes by pfn before reboot

[Vladimir Davydov <vdavydov@parallels.com>]

Since page structs, which are used for linking PRAM nodes, are cleared
on boot, organize all PRAM nodes into a list singly-linked by pfn's
before reboot to facilitate the node list restore in the new kernel.
---
 mm/pram.c |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/mm/pram.c b/mm/pram.c
index f7eebe1..c7706dc 100644
--- a/mm/pram.c
+++ b/mm/pram.c
@@ -1,11 +1,15 @@
 #include <linux/err.h>
 #include <linux/gfp.h>
 #include <linux/highmem.h>
+#include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/mm.h>
+#include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/notifier.h>
 #include <linux/pram.h>
+#include <linux/reboot.h>
 #include <linux/sched.h>
 #include <linux/string.h>
 #include <linux/types.h>
@@ -42,6 +46,9 @@ struct pram_link {
  * singly-linked list of PRAM link structures (see above), the node has a
  * pointer to the head of.
  *
+ * To facilitate data restore in the new kernel, before reboot all PRAM nodes
+ * are organized into a list singly-linked by pfn's (see pram_reboot()).
+ *
  * The structure occupies a memory page.
  */
 struct pram_node {
@@ -49,6 +56,7 @@ struct pram_node {
 	__u32	type;		/* data type, see enum pram_stream_type */
 	__u64	data_len;	/* data size, only for byte streams */
 	__u64	link_pfn;	/* points to the first link of the node */
+	__u64	node_pfn;	/* points to the next node in the node list */
 
 	__u8	name[PRAM_NAME_MAX];
 };
@@ -57,6 +65,10 @@ struct pram_node {
 #define PRAM_LOAD		2
 #define PRAM_ACCMODE_MASK	3
 
+/*
+ * For convenience sake PRAM nodes are kept in an auxiliary doubly-linked list
+ * connected through the lru field of the page struct.
+ */
 static LIST_HEAD(pram_nodes);			/* linked through page::lru */
 static DEFINE_MUTEX(pram_mutex);		/* serializes open/close */
 
@@ -521,3 +533,41 @@ size_t pram_read(struct pram_stream *ps, void *buf, size_t count)
 	}
 	return read_count;
 }
+
+/*
+ * Build the list of PRAM nodes.
+ */
+static void __pram_reboot(void)
+{
+	struct page *page;
+	struct pram_node *node;
+	unsigned long node_pfn = 0;
+
+	list_for_each_entry_reverse(page, &pram_nodes, lru) {
+		node = page_address(page);
+		if (WARN_ON(node->flags & PRAM_ACCMODE_MASK))
+			continue;
+		node->node_pfn = node_pfn;
+		node_pfn = page_to_pfn(page);
+	}
+}
+
+static int pram_reboot(struct notifier_block *notifier,
+		       unsigned long val, void *v)
+{
+	if (val != SYS_RESTART)
+		return NOTIFY_DONE;
+	__pram_reboot();
+	return NOTIFY_OK;
+}
+
+static struct notifier_block pram_reboot_notifier = {
+	.notifier_call = pram_reboot,
+};
+
+static int __init pram_init(void)
+{
+	register_reboot_notifier(&pram_reboot_notifier);
+	return 0;
+}
+module_init(pram_init);
-- 
1.7.10.4

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