[RFC PATCH v2 1/7] kexec_file: Add fdt modification callback support

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

From: Stanislav Kinsburskii <stanislav.kinsburskii@gmail.com>

Introduce primitives to:
- Register and unregister callbacks for flattened device tree (fdt)
  modifications.
- Invoke all registered callbacks.
- Check for any registered callbacks.

These enhancements enable the use of a device tree to store kernel bits.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
---
 include/linux/kexec.h |    7 +++++++
 kernel/kexec_file.c   |   24 ++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 22b5cd24f581..c9c70551796d 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -282,6 +282,13 @@ arch_kexec_apply_relocations(struct purgatory_info *pi, Elf_Shdr *section,
 	return -ENOEXEC;
 }
 #endif
+
+struct notifier_block;
+extern int register_kexec_fdt_notifier(struct notifier_block *nb);
+extern int unregister_kexec_fdt_notifier(struct notifier_block *nb);
+extern bool kexec_fdt_notify_list_empty(void);
+extern int kexec_fdt_notify(void *fdt);
+
 #endif /* CONFIG_KEXEC_FILE */
 
 #ifdef CONFIG_KEXEC_ELF
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 881ba0d1714c..f9245d5e4459 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -43,6 +43,30 @@ static int kexec_calculate_store_digests(struct kimage *image);
 /* Maximum size in bytes for kernel/initrd files. */
 #define KEXEC_FILE_SIZE_MAX	min_t(s64, 4LL << 30, SSIZE_MAX)
 
+static BLOCKING_NOTIFIER_HEAD(kexec_fdt_notify_list);
+
+bool kexec_fdt_notify_list_empty(void)
+{
+	return kexec_fdt_notify_list.head == NULL;
+}
+
+int kexec_fdt_notify(void *fdt)
+{
+	return blocking_notifier_call_chain(&kexec_fdt_notify_list, 0, fdt);
+}
+
+int register_kexec_fdt_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&kexec_fdt_notify_list, nb);
+}
+EXPORT_SYMBOL(register_kexec_fdt_notifier);
+
+int unregister_kexec_fdt_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&kexec_fdt_notify_list, nb);
+}
+EXPORT_SYMBOL(unregister_kexec_fdt_notifier);
+
 /*
  * Currently this is the only default function that is exported as some
  * architectures need it to do additional handlings.