Subject: [PATCH v4 1/7] kexec_file: add kexec_file flag to control debug printing

From: Baoquan He <[email-masked]>
Date: Wed, 13 Dec 2023 13:57:41 +0800

When specifying 'kexec -c -d', kexec_load interface will print loading
information, e.g the regions where kernel/initrd/purgatory/cmdline
are put, the memmap passed to 2nd kernel taken as system RAM ranges,
and printing all contents of struct kexec_segment, etc. These are
very helpful for analyzing or positioning what's happening when
kexec/kdump itself failed. The debugging printing for kexec_load
interface is made in user space utility kexec-tools.

Whereas, with kexec_file_load interface, 'kexec -s -d' print nothing.
Because kexec_file code is mostly implemented in kernel space, and the
debugging printing functionality is missed. It's not convenient when
debugging kexec/kdump loading and jumping with kexec_file_load
interface.

Now add KEXEC_FILE_DEBUG to kexec_file flag to control the debugging
message printing. And add global variable kexec_file_dbg_print and
macro kexec_dprintk() to facilitate the printing.

This is a preparation, later kexec_dprintk() will be used to replace the
existing pr_debug(). Once 'kexec -s -d' is specified, it will print out
kexec/kdump loading information. If '-d' is not specified, it regresses
to pr_debug().

Signed-off-by: Baoquan He <[email-masked]>
---
 include/linux/kexec.h      | 9 ++++++++-
 include/uapi/linux/kexec.h | 1 +
 kernel/kexec_core.c        | 2 ++
 kernel/kexec_file.c        | 3 +++
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 8227455192b7..400cb6c02176 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -403,7 +403,7 @@ bool kexec_load_permitted(int kexec_image_type);
 
 /* List of defined/legal kexec file flags */
 #define KEXEC_FILE_FLAGS	(KEXEC_FILE_UNLOAD | KEXEC_FILE_ON_CRASH | \
-				 KEXEC_FILE_NO_INITRAMFS)
+				 KEXEC_FILE_NO_INITRAMFS | KEXEC_FILE_DEBUG)
 
 /* flag to track if kexec reboot is in progress */
 extern bool kexec_in_progress;
@@ -500,6 +500,13 @@ static inline int crash_hotplug_memory_support(void) { return 0; }
 static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
 #endif
 
+extern bool kexec_file_dbg_print;
+
+#define kexec_dprintk(fmt, ...)					\
+	printk("%s" fmt,					\
+	       kexec_file_dbg_print ? KERN_INFO : KERN_DEBUG,	\
+	       ##__VA_ARGS__)
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
diff --git a/include/uapi/linux/kexec.h b/include/uapi/linux/kexec.h
index 01766dd839b0..c17bb096ea68 100644
--- a/include/uapi/linux/kexec.h
+++ b/include/uapi/linux/kexec.h
@@ -25,6 +25,7 @@
 #define KEXEC_FILE_UNLOAD	0x00000001
 #define KEXEC_FILE_ON_CRASH	0x00000002
 #define KEXEC_FILE_NO_INITRAMFS	0x00000004
+#define KEXEC_FILE_DEBUG	0x00000008
 
 /* These values match the ELF architecture values.
  * Unless there is a good reason that should continue to be the case.
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index be5642a4ec49..f70bf3a7885c 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -52,6 +52,8 @@ atomic_t __kexec_lock = ATOMIC_INIT(0);
 /* Flag to indicate we are going to kexec a new kernel */
 bool kexec_in_progress = false;
 
+bool kexec_file_dbg_print;
+
 int kexec_should_crash(struct task_struct *p)
 {
 	/*
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index f9a419cd22d4..aca5dac74044 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -123,6 +123,8 @@ void kimage_file_post_load_cleanup(struct kimage *image)
 	 */
 	kfree(image->image_loader_data);
 	image->image_loader_data = NULL;
+
+	kexec_file_dbg_print = false;
 }
 
 #ifdef CONFIG_KEXEC_SIG
@@ -278,6 +280,7 @@ kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
 	if (!image)
 		return -ENOMEM;
 
+	kexec_file_dbg_print = !!(flags & KEXEC_FILE_DEBUG);
 	image->file_mode = 1;
 
 	if (kexec_on_panic) {
-- 
2.41.0