kexec: move sysfs entries to /sys/kernel/kexec

kexec: move sysfs entries to /sys/kernel/kexec

Patch series "kexec: reorganize kexec and kdump sysfs", v6.

All existing kexec and kdump sysfs entries are moved to a new location,
/sys/kernel/kexec, to keep /sys/kernel/ clean and better organized.
Symlinks are created at the old locations for backward compatibility and
can be removed in the future [01/03].

While doing this cleanup, the old kexec and kdump sysfs entries are
marked as deprecated in the existing ABI documentation [02/03]. This
makes it clear that these older interfaces should no longer be used.
New ABI documentation is added to describe the reorganized interfaces
[03/03], so users and tools can rely on the updated sysfs interfaces
going forward.

This patch (of 3):

Several kexec and kdump sysfs entries are currently placed directly under
/sys/kernel/, which clutters the directory and makes it harder to identify
unrelated entries.  To improve organization and readability, these entries
are now moved under a dedicated directory, /sys/kernel/kexec.

The following sysfs moved under new kexec sysfs node
+------------------------------------+------------------+
|    Old sysfs name         |     New sysfs name        |
|  (under /sys/kernel)      | (under /sys/kernel/kexec) |
+---------------------------+---------------------------+
| kexec_loaded              | loaded                    |
+---------------------------+---------------------------+
| kexec_crash_loaded        | crash_loaded              |
+---------------------------+---------------------------+
| kexec_crash_size          | crash_size                |
+---------------------------+---------------------------+
| crash_elfcorehdr_size     | crash_elfcorehdr_size     |
+---------------------------+---------------------------+
| kexec_crash_cma_ranges    | crash_cma_ranges          |
+---------------------------+---------------------------+

For backward compatibility, symlinks are created at the old locations so
that existing tools and scripts continue to work.  These symlinks can be
removed in the future once users have switched to the new path.

While creating symlinks, entries are added in /sys/kernel/ that point to
their new locations under /sys/kernel/kexec/.  If an error occurs while
adding a symlink, it is logged but does not stop initialization of the
remaining kexec sysfs symlinks.

The /sys/kernel/<crash_elfcorehdr_size | kexec/crash_elfcorehdr_size>
entry is now controlled by CONFIG_CRASH_DUMP instead of
CONFIG_VMCORE_INFO, as CONFIG_CRASH_DUMP also enables CONFIG_VMCORE_INFO.

Link: https://lkml.kernel.org/r/20251118114507.1769455-1-sourabhjain@linux.ibm.com
Link: https://lkml.kernel.org/r/20251118114507.1769455-2-sourabhjain@linux.ibm.com
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Aditya Gupta <adityag@linux.ibm.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mahesh J Salgaonkar <mahesh@linux.ibm.com>
Cc: Pingfan Liu <piliu@redhat.com>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Shivang Upadhyay <shivangu@linux.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>