linux-kernel - Re: [PATCH] update ctime and mtime for mmaped write

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Message-ID: <45DDF9C1.4090003@redhat.com>
Date:	Thu, 22 Feb 2007 15:14:57 -0500
From:	Peter Staubach <staubach@...hat.com>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	akpm@...ux-foundation.org, hugh@...itas.com,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] update ctime and mtime for mmaped write

Miklos Szeredi wrote:
>>>> Why is the flag checked in __fput()?
>>>>     
>>>>         
>>> It's because of this bit in the standard:
>>>
>>>     If there is no such call and if the underlying file is modified
>>>     as a result of a write reference, then these fields shall be
>>>     marked for update at some time after the write reference.
>>>
>>> It could be done in munmap/mremap, but it seemed more difficult to
>>> track down all the places where the vma is removed.  But yes, that may
>>> be a nicer solution.
>>>       
>> It seems to me that, with this support, a file, which is mmap'd,
>> modified, but never msync'd or munmap'd, will never get its mtime
>> updated.  Or did I miss that?
>>
>> I also don't see how an mmap'd block device will get its mtime
>> updated either.
>>     
>
> __fput() will be called when there are no more references to 'file',
> then it will update the time if the flag is set.  This applies to
> regular files as well as devices.
>
>   

I suspect that you will find that, for a block device, the wrong inode
gets updated.  That's where the bd_inode_update_time() portion of my
proposed patch came from.

> But I've moved the check from __fput to remove_vma() in the next
> revision of the patch, which would give slightly nicer semantics, and
> be equally conforming.

This still does not address the situation where a file is 'permanently'
mmap'd, does it?

    Thanx...

       ps
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