linux-kernel - Re: [patch 1/1] PM: Adds remount fs ro at suspend

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Date:	Sat, 03 Feb 2007 15:34:57 -1000
From:	akuster <akuster@...sta.com>
To:	Christoph Hellwig <hch@...radead.org>, akuster@...sta.com,
	linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: [patch 1/1] PM: Adds remount fs ro at suspend



Christoph Hellwig wrote:
> On Fri, Feb 02, 2007 at 01:50:10PM -1000, akuster@...sta.com wrote:
>>
>> This adds the ability for the file system to remounted as read only during a
>> system suspend.  Log the mount points so when the resume occurs, they can be 
>> remounted back to their original states. This is so in an advent of a power
>> failure, we try our best to keep data from being corrupted or lost.
> 
> Can you please explain why this can't be done in userspace?  

I am sure it can.  The idea came from customer inputs, speed is my 
guess. echo mem > /sys/../state seems a whole lot simpler and cleaner 
than having userspace figure out what it mounted and then doing echo mem.

In fact
> all existing suspend solutions seem to be doing fine doing things like
> this in userspace.

I guess I missed that boat. If you don't mind, could you point at one 
solution.

> 
>> +static struct suspremount *suspremount_list;
>> +
< snipped>

>> +void suspend_remount_all_fs_ro(void)
>> +{
>> +	suspremount_list = NULL;
>> +	emergency_remount();
> 
> NACK.  emergency_remount is exactly what it sais and should never ever
> be used for a system that you want to keep on using later on.  

The code "emergency_remount" is almost identical to what we have been 
using. I wanted to reuse existing code rather than dup it.

If you
> look at it's implementation it's not correct and can't serve as more than
> a bandaid for susrq. 

 From our customer experience, we have not gotten an bad feedback on it. 
  It seems to address there needs.

  In fact we should probably just remove it..
> 
>> +EXPORT_SYMBOL(suspend_remount_all_fs_ro);
> 
> And something like this for sure should not be exported.
> 
>> +EXPORT_SYMBOL(resume_remount_fs_rw);
> 
> ditto.
> 

All the code corrects have been address in my upcoming version.

Many thanks for you time and feedback.

Armin
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