Re: [RFC] persistent store

[Tony Luck]

On Sun, Nov 21, 2010 at 5:59 PM, Huang Ying <ying.huang@xxxxxxxxx> wrote:
> This patch provides a general "read" interface for kmsg_dumper and some
> other persistent storage users. Another possible choice is to just
> extend the original interface to add persistent store support. For
> example, we can add a "read" function in kmsg_dumper, and output the
> content of persistent store via extend /dev/kmsg via prefix every line
> comes from persistent store or adding some "ioctl" to do that. (But it
> seems that nobody likes "ioctl").

In Linux (and Unix before it) "everything is a file" ... but this
doesn't work very well if the file has internal structure (e.g.
is made of records that can be individually changed or
deleted).  A filesystem seems a much better model.

>> "writer" which writes a record with a type to the persistent store
>
> I think it is necessary to require this to be NMI safe (in comments?),
> because hardware error handler may need to write to persistent storage
> in NMI context. Or we can add a "flag" field to let storage provider
> advocate its capability of NMI safe.

I can add a comment to pstore.h to document the NMI-safe
requirement for the "writer" function.

>>   - Which device(s) should error records be written to?
>>     All of them? Start with one and move on when it is
>>     full?  Write some types of records to one device?
>
> The persistent storage may be full, and the writing may fail. So I think
> we can just try to write one by one, until the first success writing.

A good option - if we ever find someone luck enough to have
more than one persistent store device.

>> +       sysfs_remove_bin_file(&pstore_kset->kobj, &search_pstore->attr);
>
> It seems that the corresponding memory is not freed after erasing.

Ouch!  Good catch.  Will add a kfree()

-Tony
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