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Subject: Re: [RFC v7 2/5] dt-bindings: pstore-block: new support for blkoops
To:     Rob Herring <robh@kernel.org>
Cc:     Kees Cook <keescook@chromium.org>,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Mark Rutland <mark.rutland@arm.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "David S. Miller" <davem@davemloft.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        devicetree@vger.kernel.org
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From:   liaoweixiong <liaoweixiong@allwinnertech.com>
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Date:   Fri, 15 Feb 2019 09:06:57 +0800
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On 2019-02-14 04:30, Rob Herring wrote:
> On Wed, Feb 13, 2019 at 7:51 AM liaoweixiong
> <liaoweixiong@allwinnertech.com> wrote:
>>
>>
>> On 2019-01-31 00:07, Rob Herring wrote:> On Wed, Jan 23, 2019 at
>> 08:05:13PM +0800, liaoweixiong wrote:
>>>> Create DT binding document for blkoops.
>>>>
>>>> Signed-off-by: liaoweixiong <liaoweixiong@allwinnertech.com>
>>>> ---
>>>>  .../devicetree/bindings/pstore-block/blkoops.txt   | 32 ++++++++++++++++++++++
>>>
>>> /bindings/pstore/...
>>>
>>> I wouldn't call it blkoops either. I believe ramoops is called that to
>>> maintain compatibility keeping the same kernel module name that
>>> preceeded pstore.
>>>
>>
>> Fixed.
>>
>> In addition, I don't known whether should we move
>> ramreserved-memory/ooos.txt to /bindings/pstore. This is for maintainer
>> to decide, and do it on other patch.
>>
>>>>  MAINTAINERS                                        |  1 +
>>>>  2 files changed, 33 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/pstore-block/blkoops.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/pstore-block/blkoops.txt b/Documentation/devicetree/bindings/pstore-block/blkoops.txt
>>>> new file mode 100644
>>>> index 0000000..a25835b
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/pstore-block/blkoops.txt
>>>> @@ -0,0 +1,32 @@
>>>> +Blkoops oops logger
>>>> +===================
>>>> +
>>>> +Blkoops provides a block partition for oops, excluding panics now, so they can
>>>> +be recovered after a reboot.
>>>> +
>>>> +Any space of block partition will be used for a circular buffer of oops records.
>>>> +These records have a configurable size, with a size of 0 indicating that they
>>>> +should be disabled.
>>>> +
>>>> +"partition-size" and at least one of "dmesg-size" or "pmsg-size" must be set
>>>> +non-zero, but are otherwise optional as listed below.
>>>> +
>>>> +Blkoops will take value from Kconfig if device tree do not set, but settings
>>>> +from module parameters can also overwrite them.
>>>
>>> That's all kernel details not relevant to the binidng.
>>>
>>
>> Deleted.
>>
>>>> +
>>>> +Required properties:
>>>> +
>>>> +- compatible: must be "blkoops".
>>>> +
>>>> +- partition-size: size in kbytes, must be a multiple of 4.
>>>
>>> This seems unnecessary given a partition has a known size.
>>>
>>
>> partition-size is necessary for psotre/blk. User should tell pstore/blk
>> how large space can it use.
> 
> The partition table says how big a partition is. If you only want to
> use part of it, then make the partition smaller or use a file system.
> This is a solved problem, so we don't need a new way in DT to handle
> this.
> 

You are right, partition size is known and pstore/blk can get it
automatically from specified block device. I will try to do it on next
version patch.
But i prefer to rename partition-size to total-size and move it to
optional properties. Total-size means how big space pstore/blk can use.
It is not only about partition size as pstore/blk can use ram if no
partition specified.
So, I will process as follow logic:
1. If specify total size, use total size.
2. If no total size but specify partition, get size from partition.

>>>> +Optional properties:
>>>> +
>>>> +- partition-path: strings must begin with "/dev", tell blkoops which partition
>>>> +  it can used. If it is not set, blkoops will drop all data when reboot.
>>>
>>> No. '/dev/...' is a Linux thing and doesn't belong in DT.
>>>
>>> You should define a partition UUID and/or label and the kernel can find
>>> the right partition to use.
>>>
>>
>> pstore/blk do general read/write by filp_open/kernel_read/kernel_write,
>> which need device path.
>> In addition, i have no idea how to use UUID and/or label to do general
>> read/write on kernel layer, can you give me a tip?
> 
> The kernel can mount a filesystem by label or UUID though I think
> those are filesystem UUID and label, not partition UUID and label. But
> certainly bootloaders find the EFI system partition by UUID.
> 

As your words, those are file system UUID and label, not partition
UUID/label. Pstore is a file system, there is no other file system any
more for specified partition. Pstore/blk can't get specified partition
by UUID or label.
As far as i know, block device manager on user space scans each block
device and matches file system table to get UUID and label. Not even all
file systems have UUID/label.
MTD device may has label, but it is not suitable for all block device.
How if i cancel the prefix requirement for /dev and add it to the codes?
Then rename partition-path to block-device, by this, DT property may be
"mmcblk0p10" or "sda6" .

> Rob
> 

-- 
liaoweixiong