linux-kernel - Re: [RFC v5 0/4] pstore/block: new support logger for block devices

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Date:   Tue, 8 Jan 2019 10:19:06 +0800
From:   廖威雄 <liaoweixiong@...winnertech.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Arnd Bergmann <arnd@...db.de>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v5 0/4] pstore/block: new support logger for block devices

On 2019-01-08 05:47, Kees Cook wrote:
> On Mon, Jan 7, 2019 at 4:01 AM liaoweixiong
> <liaoweixiong@...winnertech.com> wrote:
>>
>> Why should we need pstore_block?
>> 1. Most embedded intelligent equipment have no persistent ram, which
>> increases costs. We perfer to cheaper solutions, like block devices.
>> In fast, there is already a sample for block device logger in driver
>> MTD (drivers/mtd/mtdoops.c).
>> 2. Do not any equipment have battery, which means that it lost all data
>> on general ram if power failure. Pstore has little to do for these
>> equipments.
> 
> I'm catching up from being off over the holidays, but I just wanted to
> say that I like the general idea here.

Thanks for your work very much! :)

> 
>> [PATCH v5]
>> On patch 1:
>> 1. rename pstore/rom to pstore/blk
> 
> Thanks! The earlier name seemed wrong. :)
> 
>> 2. Do not allocate any memory in the write path of panic. So, use local
>> array instead in function romz_recover_dmesg_meta.
>> 3. Add C header file "linux/fs.h" to fix implicit declaration of function
>>    'filp_open','kernel_read'...
>> On patch 3:
>> 1. If panic, do not recover pmsg but flush if it is dirty.
>> 2. Fix erase pmsg failed.
>> On patch 4:
>> 1. Create a document for pstore/blk
> 
> Overall, I wonder if more of the ram backend code could get reused for
> the blk backend? I'd much rather be able to share that, since much of
> the logic is the same.

Before I wrote pstore/blk, I specially studied pstore/ram. As your
words, much of the logic is the same, you will see some codes similar to
pstore/ram.
But there is still something different with pstore/ram. For example,
block device maybe unready for read/write before kernel finish
initializing. So, pstore/blk recovers old data when  mount rather than
initialize.
In addition, pstore/blk could not be used for pstore-console, since
block device much slower than ram.
In my original design, pstore/blk works like a manager for storage
space, don't care if it is ram or block device. So, it may works for
persistent ram too.

> 
> I'll get to a more detailed review in the coming days. Thanks for sending this!
> 
> -Kees
> 
>>
>> [PATCH v4]
>> On patch 1:
>> 1. Fix always true condition '(--i >= 0) => (0-u32max >= 0)' in function
>>    romz_init_zones by defining variable i to 'int' rahter than
>>    'unsigned int'.
>> 2. To make codes more easily to read, we use macro READ_NEXT_ZONE for
>>    return value of romz_dmesg_read if it need to read next zone.
>>    Moveover, we assign READ_NEXT_ZONE -1024 rather than 0.
>> 3. Add 'FLUSH_META' to 'enum romz_flush_mode' and rename 'NOT_FLUSH' to
>>    'FLUSH_NONE'
>> 4. Function romz_zone_write work badly with FLUSH_PART mode as badly
>>    address and offset to write.
>> On patch 3:
>> NEW SUPPORT psmg for pstore_rom.
>>
>> [PATCH v3]
>> On patch 1:
>> Fix build as module error for undefined 'vfs_read' and 'vfs_write'
>> Both of 'vfs_read' and 'vfs_write' haven't be exproted yet, so we use
>> 'kernel_read' and 'kernel_write' instead.
>>
>> [PATCH v2]
>> On patch 1:
>> Fix build as module error for redefinition of 'romz_unregister' and
>> 'romz_register'
>>
>> [PATCH v1]
>> On patch 1:
>> Core codes of pstore_rom, which works well on allwinner(sunxi) platform.
>> On patch 2:
>> A sample for pstore_rom, using general ram rather than block device.
>>
>> liaoweixiong (4):
>>   pstore/blk: new support logger for block devices
>>   pstore/blk: add sample for pstore_blk
>>   pstore/blk: support pmsg for pstore block
>>   Documentation: pstore/blk: create document for pstore_blk
>>
>>  Documentation/admin-guide/pstore-block.rst |  226 ++++++
>>  MAINTAINERS                                |    1 +
>>  fs/pstore/Kconfig                          |   20 +
>>  fs/pstore/Makefile                         |    5 +
>>  fs/pstore/blkbuf.c                         |   46 ++
>>  fs/pstore/blkzone.c                        | 1168 ++++++++++++++++++++++++++++
>>  include/linux/pstore_blk.h                 |   62 ++
>>  7 files changed, 1528 insertions(+)
>>  create mode 100644 Documentation/admin-guide/pstore-block.rst
>>  create mode 100644 fs/pstore/blkbuf.c
>>  create mode 100644 fs/pstore/blkzone.c
>>  create mode 100644 include/linux/pstore_blk.h
>>
>> --
>> 1.9.1
>>
> 
>