linux-kernel - [PATCH v2 4/5] kexec: document new kexec and kdump sysfs ABIs

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Message-ID: <20251106045107.17813-5-sourabhjain@linux.ibm.com>
Date: Thu,  6 Nov 2025 10:21:06 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Aditya Gupta <adityag@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, Baoquan he <bhe@...hat.com>,
        Dave Young <dyoung@...hat.com>, Hari Bathini <hbathini@...ux.ibm.com>,
        Jiri Bohac <jbohac@...e.cz>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Pingfan Liu <piliu@...hat.com>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Shivang Upadhyay <shivangu@...ux.ibm.com>,
        Vivek Goyal <vgoyal@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
        kexec@...ts.infradead.org
Subject: [PATCH v2 4/5] kexec: document new kexec and kdump sysfs ABIs

Add an ABI document for following kexec and kdump sysfs interface:

- /sys/kernel/kexec/loaded
- /sys/kernel/kexec/crash_loaded
- /sys/kernel/kexec/crash_size
- /sys/kernel/kexec/crash_elfcorehdr_size

Cc: Aditya Gupta <adityag@...ux.ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Baoquan he <bhe@...hat.com>
Cc: Dave Young <dyoung@...hat.com>
Cc: Hari Bathini <hbathini@...ux.ibm.com>
Cc: Jiri Bohac <jbohac@...e.cz>
Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
Cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>
Cc: Pingfan Liu <piliu@...hat.com>
Cc: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Cc: Shivang Upadhyay <shivangu@...ux.ibm.com>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: kexec@...ts.infradead.org
Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
---
 .../ABI/testing/sysfs-kernel-kexec-kdump      | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-kexec-kdump

diff --git a/Documentation/ABI/testing/sysfs-kernel-kexec-kdump b/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
new file mode 100644
index 000000000000..00c00f380fea
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
@@ -0,0 +1,51 @@
+What:		/sys/kernel/kexec/*
+Date:		Nov 2025
+Contact:	kexec@...ts.infradead.org
+Description:
+		The /sys/kernel/kexec/* directory contains sysfs files
+		that provide information about the configuration status
+		of kexec and kdump.
+
+What:		/sys/kernel/kexec/loaded
+Date:		Nov 2025
+Contact:	kexec@...ts.infradead.org
+Description:	read only
+		Indicates whether a new kernel image has been loaded
+		into memory using the kexec system call. It shows 1 if
+		a kexec image is present and ready to boot, or 0 if none
+		is loaded.
+User:		kexec tools, kdump service
+
+What:		/sys/kernel/kexec/crash_loaded
+Date:		Nov 2025
+Contact:	kexec@...ts.infradead.org
+Description:	read only
+		Indicates whether a crash (kdump) kernel is currently
+		loaded into memory. It shows 1 if a crash kernel has been
+		successfully loaded for panic handling, or 0 if no crash
+		kernel is present.
+User:		Kexec tools, Kdump service
+
+What:		/sys/kernel/kexec/crash_size
+Date:		Nov 2025
+Contact:	kexec@...ts.infradead.org
+Description:	read/write
+		Shows the amount of memory reserved for loading the crash
+		(kdump) kernel. It reports the size, in bytes, of the
+		crash kernel area defined by the crashkernel= parameter.
+		This interface also allows reducing the crashkernel
+		reservation by writing a smaller value, and the reclaimed
+		space is added back to the system RAM.
+User:		Kdump service
+
+What:		/sys/kernel/kexec/crash_elfcorehdr_size
+Date:		Nov 2025
+Contact:	kexec@...ts.infradead.org
+Description:	read only
+		Indicates the preferred size of the memory buffer for the
+		ELF core header used by the crash (kdump) kernel. It defines
+		how much space is needed to hold metadata about the crashed
+		system, including CPU and memory information. This information
+		is used by the user space utility kexec to support updating the
+		in-kernel kdump image during hotplug operations.
+User:		Kexec tools
-- 
2.51.0