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 <kernelf...@gmail.com>
Cc: Bhupesh Sharma <bhupesh.sha...@linaro.org>
Cc: Kazuhito Hagio <k-ha...@ab.jp.nec.com>
Cc: Dave Young <dyo...@redhat.com>
Cc: Baoquan He <b...@redhat.com>
Cc: Boris Petkov <b...@alien8.de>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: James Morse <james.mo...@arm.com>
Cc: Mark Rutland <mark.rutl...@arm.com>
Cc: Will Deacon <w...@kernel.org>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Dave Anderson <ander...@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-ker...@vger.kernel.org
Cc: ke...@lists.infradead.org
Cc: x...@kernel.org
Cc: linux-arm-ker...@lists.infradead.org
---
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
