88 lines
3.7 KiB
Plaintext
88 lines
3.7 KiB
Plaintext
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s390 SCSI dump tool (zfcpdump)
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System z machines (z900 or higher) provide hardware support for creating system
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dumps on SCSI disks. The dump process is initiated by booting a dump tool, which
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has to create a dump of the current (probably crashed) Linux image. In order to
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not overwrite memory of the crashed Linux with data of the dump tool, the
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hardware saves some memory plus the register sets of the boot cpu before the
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dump tool is loaded. There exists an SCLP hardware interface to obtain the saved
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memory afterwards. Currently 32 MB are saved.
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This zfcpdump implementation consists of a Linux dump kernel together with
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a userspace dump tool, which are loaded together into the saved memory region
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below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in
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the s390-tools package) to make the device bootable. The operator of a Linux
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system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump
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resides on.
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The kernel part of zfcpdump is implemented as a debugfs file under "zcore/mem",
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which exports memory and registers of the crashed Linux in an s390
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standalone dump format. It can be used in the same way as e.g. /dev/mem. The
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dump format defines a 4K header followed by plain uncompressed memory. The
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register sets are stored in the prefix pages of the respective cpus. To build a
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dump enabled kernel with the zcore driver, the kernel config option
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CONFIG_ZFCPDUMP has to be set. When reading from "zcore/mem", the part of
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memory, which has been saved by hardware is read by the driver via the SCLP
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hardware interface. The second part is just copied from the non overwritten real
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memory.
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The userspace application of zfcpdump can reside e.g. in an intitramfs or an
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initrd. It reads from zcore/mem and writes the system dump to a file on a
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SCSI disk.
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To build a zfcpdump kernel use the following settings in your kernel
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configuration:
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* CONFIG_ZFCPDUMP=y
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* Enable ZFCP driver
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* Enable SCSI driver
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* Enable ext2 and ext3 filesystems
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* Disable as many features as possible to keep the kernel small.
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E.g. network support is not needed at all.
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To use the zfcpdump userspace application in an initramfs you have to do the
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following:
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* Copy the zfcpdump executable somewhere into your Linux tree.
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E.g. to "arch/s390/boot/zfcpdump. If you do not want to include
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shared libraries, compile the tool with the "-static" gcc option.
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* If you want to include e2fsck, add it to your source tree, too. The zfcpdump
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application attempts to start /sbin/e2fsck from the ramdisk.
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* Use an initramfs config file like the following:
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dir /dev 755 0 0
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nod /dev/console 644 0 0 c 5 1
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nod /dev/null 644 0 0 c 1 3
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nod /dev/sda1 644 0 0 b 8 1
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nod /dev/sda2 644 0 0 b 8 2
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nod /dev/sda3 644 0 0 b 8 3
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nod /dev/sda4 644 0 0 b 8 4
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nod /dev/sda5 644 0 0 b 8 5
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nod /dev/sda6 644 0 0 b 8 6
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nod /dev/sda7 644 0 0 b 8 7
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nod /dev/sda8 644 0 0 b 8 8
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nod /dev/sda9 644 0 0 b 8 9
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nod /dev/sda10 644 0 0 b 8 10
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nod /dev/sda11 644 0 0 b 8 11
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nod /dev/sda12 644 0 0 b 8 12
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nod /dev/sda13 644 0 0 b 8 13
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nod /dev/sda14 644 0 0 b 8 14
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nod /dev/sda15 644 0 0 b 8 15
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file /init arch/s390/boot/zfcpdump 755 0 0
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file /sbin/e2fsck arch/s390/boot/e2fsck 755 0 0
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dir /proc 755 0 0
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dir /sys 755 0 0
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dir /mnt 755 0 0
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dir /sbin 755 0 0
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* Issue "make image" to build the zfcpdump image with initramfs.
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In a Linux distribution the zfcpdump enabled kernel image must be copied to
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/usr/share/zfcpdump/zfcpdump.image, where the s390 zipl tool is looking for the
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dump kernel when preparing a SCSI dump disk.
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If you use a ramdisk copy it to "/usr/share/zfcpdump/zfcpdump.rd".
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For more information on how to use zfcpdump refer to the s390 'Using the Dump
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Tools book', which is available from
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http://www.ibm.com/developerworks/linux/linux390.
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