Date:	Thu, 28 Jul 2016 01:18:42 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	kvm@...r.kernel.org, qemu-devel@...gnu.org,
	virtualization@...ts.linux-foundation.org,
	Tony Luck <tony.luck@...el.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Anton Vorontsov <anton@...msg.org>,
	Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Minchan Kim <minchan@...nel.org>,
	Anthony Liguori <aliguori@...zon.com>,
	Colin Cross <ccross@...roid.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC/PATCHSET 0/7] virtio: Implement virtio pstore device (v2)

On Thu, Jul 28, 2016 at 12:08:24AM +0900, Namhyung Kim wrote:
> Hello,
> 
> This is v2 of the virtio-pstore work.  In this patchset I addressed
> most of feedbacks from previous version.  Limiting disk size is not
> implemented yet.

For some reason, only parts of the patchset were received.
Pls post all patches to all lists.

If you are changing the virtio interface with host,
like a new device, they you must copy the virtio TC
so make sure there are no objections from there.

https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback



>  * 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 0001-0003 are preparation for pstore to support virtio
> device which requires async write.  The patch 0004 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 0005 adds support for PSTORE_TYPE_CONSOLE which was
> requested by Kees.  The console data is appended to a single file for
> now.
> 
> The patch 0006 and 0007 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+ (namhyung@...jae) (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] usable
>   <6>[    0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
>   <6>[    0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
>   <6>[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000007fddfff] usable
>   <6>[    0.000000] BIOS-e820: [mem 0x0000000007fde000-0x0000000007ffffff] reserved
>   <6>[    0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
>   <6>[    0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
>   <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
>   ...
> 
> To enable PSTORE_TYPE_CONSOLE, add 'console=true' to virtio-pstore
> device option.  Also 'bufsize' option can set different size for
> pstore buffer (default is 16K).  Maybe we can add a config option to
> control the compression later.
> 
> Currently the kvmtool doesn't support any options except the directory
> the pstore saves the logs.
> 
> 
> Namhyung Kim (7):
>   pstore: Split pstore fragile flags
>   pstore/ram: Set pstore flags dynamically
>   pstore: Manage buffer position for async write
>   virtio: Basic implementation of virtio pstore driver
>   virtio-pstore: Support PSTORE_TYPE_CONSOLE
>   qemu: Implement virtio-pstore device
>   kvmtool: Implement virtio-pstore device
> 
>  drivers/acpi/apei/erst.c             |   2 +-
>  drivers/firmware/efi/efi-pstore.c    |   4 +-
>  drivers/virtio/Kconfig               |  10 +
>  drivers/virtio/Makefile              |   1 +
>  drivers/virtio/virtio_pstore.c       | 421 +++++++++++++++++++++
>  fs/pstore/platform.c                 |  65 +++-
>  fs/pstore/ram.c                      |   8 +
>  include/linux/pstore.h               |   9 +-
>  include/uapi/linux/Kbuild            |   1 +
>  include/uapi/linux/virtio_ids.h      |   1 +
>  include/uapi/linux/virtio_pstore.h   |  78 +++-
>  11 files changed, 580 insertions(+), 20 deletions(-)
>  create mode 100644 drivers/virtio/virtio_pstore.c
>  create mode 100644 include/uapi/linux/virtio_pstore.h
> 
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Anthony Liguori <aliguori@...zon.com>
> Cc: Anton Vorontsov <anton@...msg.org>
> Cc: Colin Cross <ccross@...roid.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: kvm@...r.kernel.org
> Cc: qemu-devel@...gnu.org
> Cc: virtualization@...ts.linux-foundation.org
> 
> Thanks,
> Namhyung
> 
> 
> -- 
> 2.8.0
> 
> _______________________________________________
> Virtualization mailing list
> Virtualization@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization

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