linux-kernel - Re: [PATCH] fuse: Add support for fuse stacked I/O

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Date:	Mon, 18 Jan 2016 18:57:47 -0800
From:	Nikhilesh Reddy <reddyn@...eaurora.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Nikolaus Rath <nikolaus@...h.org>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>, Jan Kara <jack@...e.cz>,
	Theodore Ts'o <tytso@....edu>, sven.utcke@....de,
	Miklos Szeredi <miklos@...redi.hu>,
	Richard Weinberger <richard@....at>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Antonio SJ Musumeci <trapexit@...wn.link>
Subject: Re: [PATCH] fuse: Add support for fuse stacked I/O

On 01/15/2016 01:53 PM, Linus Torvalds wrote:
> On Fri, Jan 15, 2016 at 1:46 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
>> If mmap sets vm_file to the underlying thing, wouldn't CRIU and
>> anything else that uses map_files get confused?  Or did you have
>> something else in mind?
>
> Why would they care?
>
> Also, I don't think you actually need to change vm_file - we have this
> whole notion of "inode->i_data" vs "inode->i_mapping".
>
> So I think you could set the "i_mapping" of the fuse inode to be the
> i_mapping of the passed-through-to inode, and it should just work.
>
> And no, I didn't look into this very deeply, and maybe there is some
> annoying detail that would make that not work well. But that's part of
> the whole point of the i_mapping indirection: so that you can share
> the page cache when you have two separate anchor points. I think coda
> uses it for the local caching, and block devices use it to not have
> mapping aliases between different inodex that all are the same block
> device.
>
>                   Linus
>

Hi

Thanks for your support.

I am looking  into adding the mmap by change the i_mmaping but seems to 
be getting stuck for some stress tests.

Once i get that debugged and working i will definitely send out a new 
patch with that functionality.

( Sending it as a second patch will help make it easier to go through 
the legal redtape and procedures i am forced to follow).

For now i am going to update the current patch and call it "passthrough" 
as you suggested and also update the commit message giving  a clearer 
explanation of the motivation.

Once i get it tested I can send it out for consideration and review

Please do let me know if you have any questions or concerns on this and 
i will try my best to address them all.


-- 
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.