s390/zfcpdump: Update documentation in zfcpdump.txt

Do the following changes:

 - Document new /proc/vmcore interface
 - Document partition dump external initramfs with s390-tools-1.24.0
 - Remove initramfs config file because initramfs is now built automatically
   in s390-tools
 - Replace description of kernel config options with "make zfcpdump_defconfig"
 - Some editorial changes

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Documentation/s390/zfcpdump.txt

@@ -1,15 +1,15 @@
-s390 SCSI dump tool (zfcpdump)
+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
+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 userspace dump tool, which are loaded together into the saved memory region
+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
@@ -19,68 +19,33 @@ The kernel part of zfcpdump is implemented as a debugfs file under "zcore/mem",
 which exports memory and registers of the crashed Linux in an s390
 standalone dump format. It can be used in the same way as e.g. /dev/mem. The
 dump format defines a 4K header followed by plain uncompressed memory. The
-register sets are stored in the prefix pages of the respective cpus. To build a
+register sets are stored in the prefix pages of the respective CPUs. To build a
 dump enabled kernel with the zcore driver, the kernel config option
 CONFIG_CRASH_DUMP has to be set. When reading from "zcore/mem", the part of
 memory, which has been saved by hardware is read by the driver via the SCLP
 hardware interface. The second part is just copied from the non overwritten real
 memory.
 
-The userspace application of zfcpdump can reside e.g. in an intitramfs or an
-initrd. It reads from zcore/mem and writes the system dump to a file on a
-SCSI disk.
+Since kernel version 3.12 also the /proc/vmcore file can also be used to access
+the dump.
 
-To build a zfcpdump kernel use the following settings in your kernel
-configuration:
- * CONFIG_CRASH_DUMP=y
- * Enable ZFCP driver
- * Enable SCSI driver
- * Enable ext2 and ext3 filesystems
- * Disable as many features as possible to keep the kernel small.
-   E.g. network support is not needed at all.
+To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig".
 
-To use the zfcpdump userspace application in an initramfs you have to do the
-following:
+The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs
+under the following locations:
 
- * Copy the zfcpdump executable somewhere into your Linux tree.
-   E.g. to "arch/s390/boot/zfcpdump. If you do not want to include
-   shared libraries, compile the tool with the "-static" gcc option.
- * If you want to include e2fsck, add it to your source tree, too. The zfcpdump
-   application attempts to start /sbin/e2fsck from the ramdisk.
- * Use an initramfs config file like the following:
+* kernel:  <zfcpdump directory>/zfcpdump.image
+* ramdisk: <zfcpdump directory>/zfcpdump.rd
 
-   dir /dev 755 0 0
-   nod /dev/console 644 0 0 c 5 1
-   nod /dev/null 644 0 0 c 1 3
-   nod /dev/sda1 644 0 0 b 8 1
-   nod /dev/sda2 644 0 0 b 8 2
-   nod /dev/sda3 644 0 0 b 8 3
-   nod /dev/sda4 644 0 0 b 8 4
-   nod /dev/sda5 644 0 0 b 8 5
-   nod /dev/sda6 644 0 0 b 8 6
-   nod /dev/sda7 644 0 0 b 8 7
-   nod /dev/sda8 644 0 0 b 8 8
-   nod /dev/sda9 644 0 0 b 8 9
-   nod /dev/sda10 644 0 0 b 8 10
-   nod /dev/sda11 644 0 0 b 8 11
-   nod /dev/sda12 644 0 0 b 8 12
-   nod /dev/sda13 644 0 0 b 8 13
-   nod /dev/sda14 644 0 0 b 8 14
-   nod /dev/sda15 644 0 0 b 8 15
-   file /init arch/s390/boot/zfcpdump 755 0 0
-   file /sbin/e2fsck arch/s390/boot/e2fsck 755 0 0
-   dir /proc 755 0 0
-   dir /sys 755 0 0
-   dir /mnt 755 0 0
-   dir /sbin 755 0 0
+The zfcpdump directory is defined in the s390-tools package.
 
- * Issue "make image" to build the zfcpdump image with initramfs.
+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.
 
-In a Linux distribution the zfcpdump enabled kernel image must be copied to
-/usr/share/zfcpdump/zfcpdump.image, where the s390 zipl tool is looking for the
-dump kernel when preparing a SCSI dump disk.
-
-If you use a ramdisk copy it to "/usr/share/zfcpdump/zfcpdump.rd".
+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