docs: move s390 under arch

and fix all in-tree references.

Architecture-specific documentation is being moved into Documentation/arch/
as a way of cleaning up the top-level documentation directory and making
the docs hierarchy more closely match the source hierarchy.

Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20230718045550.495428-1-costa.shul@redhat.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/Documentation/arch/s390/zfcpdump.rst b/Documentation/arch/s390/zfcpdump.rst
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+==================================
+The s390 SCSI dump tool (zfcpdump)
+==================================
+
+System z machines (z900 or higher) provide hardware support for creating system
+dumps on SCSI disks. The dump process is initiated by booting a dump tool, which
+has to create a dump of the current (probably crashed) Linux image. In order to
+not overwrite memory of the crashed Linux with data of the dump tool, the
+hardware saves some memory plus the register sets of the boot CPU before the
+dump tool is loaded. There exists an SCLP hardware interface to obtain the saved
+memory afterwards. Currently 32 MB are saved.
+
+This zfcpdump implementation consists of a Linux dump kernel together with
+a user space dump tool, which are loaded together into the saved memory region
+below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in
+the s390-tools package) to make the device bootable. The operator of a Linux
+system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump
+resides on.
+
+The user space dump tool accesses the memory of the crashed system by means
+of the /proc/vmcore interface. This interface exports the crashed system's
+memory and registers in ELF core dump format. To access the memory which has
+been saved by the hardware SCLP requests will be created at the time the data
+is needed by /proc/vmcore. The tail part of the crashed systems memory which
+has not been stashed by hardware can just be copied from real memory.
+
+To build a dump enabled kernel the kernel config option CONFIG_CRASH_DUMP
+has to be set.
+
+To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig".
+
+The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs
+under the following locations:
+
+* kernel:  <zfcpdump directory>/zfcpdump.image
+* ramdisk: <zfcpdump directory>/zfcpdump.rd
+
+The zfcpdump directory is defined in the s390-tools package.
+
+The user space application of zfcpdump can reside in an intitramfs or an
+initrd. It can also be included in a built-in kernel initramfs. The application
+reads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk.
+
+The s390-tools package version 1.24.0 and above builds an external zfcpdump
+initramfs with a user space application that writes the dump to a SCSI
+partition.
+
+For more information on how to use zfcpdump refer to the s390 'Using the Dump
+Tools' book, which is available from IBM Knowledge Center:
+https://www.ibm.com/support/knowledgecenter/linuxonibm/liaaf/lnz_r_dt.html