linux-kernel - Re: [PATCH] pramdisk: new block disk driver to perform persistent storage

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Message-ID: <CAPcyv4gA4zs1Y4dosZ+5rkcuRbY7=R12JP1EnJ4J4ktjg9NVSg@mail.gmail.com>
Date:	Fri, 18 Sep 2015 09:41:43 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Lin Yongting <linyongting@...wei.com>, Jens Axboe <axboe@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Weinberger <richard@....at>,
	Matthew Wilcox <willy@...ux.intel.com>, wangxiaozhe@...wei.com,
	Ingo Molnar <mingo@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pramdisk: new block disk driver to perform persistent storage

On Fri, Sep 18, 2015 at 9:18 AM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> On Fri, Sep 18, 2015 at 03:46:30PM +0800, Lin Yongting wrote:
>> In embed devices, user space applications will use reserved memory
>> (i.e. persistent memory) to store business data, the data is kept
>> in this memory region after system rebooting or panic.
>>
>> pramdisk is a block disk driver based on Persistent memory, it provide
>> file system interface for application to read/write data in persistent
>> memory. Application can use pramdisk to store log file or business data
>> in persistent memory in the way of file system operation, avoid operating
>> or managing memory directly.
>>
>> pramdisk support multiple Persistent menory regions and each one is a
>> block device named as /dev/pram<N>.
>>
>> Usage:
>> modprobe pramdisk.ko pmem=<size1>@<addr2> [ pmem=<size2>@<addr2> ... ]
>>
>> For example:
>>   modprobe pramdisk.ko pmem=20M@...0M pmem=20M@...0M
>>   mkfs.ext3 /dev/pram1
>>   mkdir /tmp/test1
>>   mount -t ext3 /dev/pram1 /tmp/test1
>>
>> Signed-off-by: Lin Yongting <linyongting@...wei.com>
>> Signed-off-by: Wang xiaozhe <wangxiaozhe@...wei.com>
>
> I think you already have this functionality with the PMEM driver and the
> memmap=nn[KMG]!ss[KMG] command line parameter?  What are you trying to
> accomplish with this driver that you can't do with PMEM?

Moreover, if your embedded firmware publishes persistent memory ranges
you can reuse the drivers/nvdimm/e820.c driver.  As long as your
platform code in the kernel names those iomem_resource(s) as
""Persistent Memory (legacy)" they will be auto discovered and
surfaced by the libnvidmm sub-system.
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