[PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Pingfan Liu]

As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
formula:
    #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)

Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
PAGES_PER_SECTION in makedumpfile just like kernel.

Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
SECTION_SIZE_BITS"). But user space wants a stable interface to get this
info. Such info is impossible to be deduced from a crashdump vmcore.
Hence append SECTION_SIZE_BITS to vmcoreinfo.

Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: Bhupesh Sharma <bhupesh.sharma@xxxxxxxxxx>
Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Boris Petkov <bp@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Dave Anderson <anderson@xxxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
---
 kernel/crash_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 825284baaf46..684a6061a13a 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -464,6 +464,7 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
 	VMCOREINFO_STRUCT_SIZE(mem_section);
 	VMCOREINFO_OFFSET(mem_section, section_mem_map);
+	VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
 	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
 #endif
 	VMCOREINFO_STRUCT_SIZE(page);
-- 
2.29.2