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[Qemu-devel] [RFC/PATCHSET 0/3] virtio: Implement virtio pstore device (

From: Namhyung Kim
Subject: [Qemu-devel] [RFC/PATCHSET 0/3] virtio: Implement virtio pstore device (v5)
Date: Sun, 4 Sep 2016 23:38:57 +0900


This is another iteration of the virtio-pstore work.  I've addressed
comments from Michael S. Tsirkin on the kernel code.

 * changes in v5)
  - convert __virtioXX to __leXX  (Michael)

 * changes in v4)
  - use qio_channel_file_new_path()  (Daniel)
  - rename to delete_old_pstore_file  (Daniel)
  - convert G_REMOVE_SOURCE to FALSE  (Daniel)

 * changes in v3)
  - use QIOChannel API  (Stefan, Daniel)
  - add bound check for malcious guests  (Daniel)
  - drop support PSTORE_TYPE_CONSOLE for now
  - update license to allow GPL v2 or later  (Michael)
  - limit number of pstore files on qemu

 * changes in v2)
  - update VIRTIO_ID_PSTORE to 22  (Cornelia, Stefan)
  - make buffer size configurable  (Cornelia)
  - support PSTORE_TYPE_CONSOLE  (Kees)
  - use separate virtqueues for read and write
  - support concurrent async write
  - manage pstore (file) id in device side
  - fix various mistakes in qemu device  (Stefan)

It started from the fact that dumping ftrace buffer at kernel
oops/panic takes too much time.  Although there's a way to reduce the
size of the original data, sometimes I want to have the information as
many as possible.  Maybe kexec/kdump can solve this problem but it
consumes some portion of guest memory so I'd like to avoid it.  And I
know the qemu + crashtool can dump and analyze the whole guest memory
including the ftrace buffer without wasting guest memory, but it adds
one more layer and has some limitation as an out-of-tree tool like not
being in sync with the kernel changes.

So I think it'd be great using the pstore interface to dump guest
kernel data on the host.  One can read the data on the host directly
or on the guest (at the next boot) using pstore filesystem as usual.
While this patchset only implements dumping kernel log buffer, it can
be extended to have ftrace buffer and probably some more..

The patch 0001 implements virtio pstore driver.  It has two virt queue
for (sync) read and (async) write, pstore buffer and io request and
response structure.  The virtio_pstore_req struct is to give
information about the current pstore operation.  The result will be
written to the virtio_pstore_res struct.  For read operation it also
uses virtio_pstore_fileinfo struct.

The patch 0002 and 0003 implement virtio-pstore legacy PCI device on
qemu-kvm and kvmtool respectively.  I referenced virtio-baloon and
virtio-rng implementations and I don't know whether kvmtool supports
modern virtio 1.0+ spec.  Other transports might be supported later.

For example, using virtio-pstore on qemu looks like below:

  $ qemu-system-x86_64 -enable-kvm -device virtio-pstore,directory=xxx

When guest kernel gets panic the log messages will be saved under the
xxx directory.

  $ ls xxx
  dmesg-1.enc.z  dmesg-2.enc.z

As you can see the pstore subsystem compresses the log data using zlib
(now supports lzo and lz4 too).  The data can be extracted with the
following command:

  $ cat xxx/dmesg-1.enc.z | \
  > python -c 'import sys, zlib; print(zlib.decompress(sys.stdin.read()))'
  Oops#1 Part1
  <5>[    0.000000] Linux version 4.6.0kvm+ (address@hidden) (gcc version 5.3.0 
(GCC) ) #145 SMP Mon Jul 18 10:22:45 KST 2016
  <6>[    0.000000] Command line: root=/dev/vda console=ttyS0
  <6>[    0.000000] x86/fpu: Legacy x87 FPU detected.
  <6>[    0.000000] x86/fpu: Using 'eager' FPU context switches.
  <6>[    0.000000] e820: BIOS-provided physical RAM map:
  <6>[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] 
  <6>[    0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] 
  <6>[    0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] 
  <6>[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000007fddfff] 
  <6>[    0.000000] BIOS-e820: [mem 0x0000000007fde000-0x0000000007ffffff] 
  <6>[    0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] 
  <6>[    0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] 
  <6>[    0.000000] NX (Execute Disable) protection: active
  <6>[    0.000000] SMBIOS 2.8 present.
  <7>[    0.000000] DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014

Namhyung Kim (3):
  virtio: Basic implementation of virtio pstore driver
  qemu: Implement virtio-pstore device
  kvmtool: Implement virtio-pstore device

 drivers/virtio/Kconfig             |  10 +
 drivers/virtio/Makefile            |   1 +
 drivers/virtio/virtio_pstore.c     | 417 +++++++++++++++++++++++++++++++++++++
 include/uapi/linux/Kbuild          |   1 +
 include/uapi/linux/virtio_ids.h    |   1 +
 include/uapi/linux/virtio_pstore.h |  74 +++++++
 6 files changed, 504 insertions(+)
 create mode 100644 drivers/virtio/virtio_pstore.c
 create mode 100644 include/uapi/linux/virtio_pstore.h

Cc: Paolo Bonzini <address@hidden>
Cc: Radim Krčmář <address@hidden>
Cc: "Michael S. Tsirkin" <address@hidden>
Cc: Anthony Liguori <address@hidden>
Cc: Anton Vorontsov <address@hidden>
Cc: Colin Cross <address@hidden>
Cc: Kees Cook <address@hidden>
Cc: Tony Luck <address@hidden>
Cc: Steven Rostedt <address@hidden>
Cc: Ingo Molnar <address@hidden>
Cc: Minchan Kim <address@hidden>
Cc: Will Deacon <address@hidden>
Cc: address@hidden
Cc: address@hidden
Cc: address@hidden
Cc: address@hidden



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