linux-kernel - Re: Are there u32 atomic bitops? (or dealing w/ i

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Message-ID: <CALCETrXMPyRC_JNnU_UExqPTMU=Wf+m0tn9fN+dgxKEd5+OO7Q@mail.gmail.com>
Date:	Thu, 20 Dec 2012 15:42:24 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Chinner <david@...morbit.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: Are there u32 atomic bitops? (or dealing w/ i_flags)

On Thu, Dec 20, 2012 at 3:36 PM, Dave Chinner <david@...morbit.com> wrote:
> On Thu, Dec 20, 2012 at 12:05:09PM -0800, Andy Lutomirski wrote:
>> On Wed, Dec 19, 2012 at 11:03 PM, Dave Chinner <david@...morbit.com> wrote:
>> start_this_handle jbd2__journal_start jbd2_journal_start
>> ext4_journal_start_sb ext4_dirty_inode __mark_inode_dirty update_time
>> file_update_time ext4_page_mkwrite do_wp_page handle_pte_fault
>> handle_mm_fault
>
> Yup, as I suspected. It's a filesystem specific problem.
>
>> This is a showstopper for my software -- I'm running on a kernel with
>> the call to file_update_time commented out.
>
> Which means you are effectively running with O_CMTIME on all mmapped
> files....

Indeed.  I'm not thrilled by not having timestamps update, and IMO
adding O_CMTIME as part of the API seems like a silly way to "fix"
this.  I'd rather fix the implementation.

The problems may be fs-specific in the sense that an fs could fix them
internally, but I think something like my AS_CMTIME approach could fix
it everywhere with much less complexity.  Any thoughts on my patch
set?  (Are you the right person to review it?)

--Andy
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