linux-kernel - Re: splice methods in character device driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4A0AFC62.3090002@pentek.com>
Date:	Wed, 13 May 2009 12:59:14 -0400
From:	Steve Rottinger <steve@...tek.com>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: splice methods in character device driver

Thanks!  This really helped me to progress using this interface.  My
current problem
is passing in the pages into splice_to_pipe.  The pages are associated
with a PCI BAR,
not main memory.  I'm wondering if this could be a problem?  Within my
driver, I use
ioremap() to map in the desired PCI BAR space; then, use virt_to_page()
to generate the
page table, based on the address returned from ioremap().   I can see
the correct pages
being received on the other end (by instrumenting the splice_to_file()
routine).  However,
the data in the resulting outfile does not match the data contained
within in my PCI BAR. I
see that splice_to_file() uses kmap_atomic() to mapping in the page,
before performing a
memcpy.  Is this going to be valid on an page that doesn't reside in
main memory?


Jens Axboe wrote:
> On Mon, May 11 2009, Steve Rottinger wrote:
>   
>> Hi,
>>
>> Has anyone successfully implemented the splice() method's in a character
>> device driver?
>> I'm having a tough time finding any existing drivers that implement
>> these method's, which
>> I can use as an example. Specifically, it is unclear to me, as to how I
>> need to set up .ops
>> in the splice_pipe_desc, when using splice_to_pipe(). 
>> My ultimate goal is to use splice to move data from a high speed data
>> acquisition device,
>> which has a buffer in PCI space to disk without the need for going
>> through block memory.
>>     
>
> I implemented ->splice_write() for /dev/null for testing purposes, but I
> doubt that you'll find much inspiration there.
>
> To use splice_to_pipe(), basically all you need to do is provide some
> way of stuffing the data pages in question into a struct page *pages[].
> See fs/splice.c:vmsplice_to_pipe(), for instance. Then you need to
> provide a way to ensure that these pages can be settled if they need to
> be accessed. Splice doesn't require that the IO is completed on the
> pages before they are put in the pipe, that's part of the power of the
> design. So if your design is allocating the pages in the ->splice_read()
> handler and initiating IO to these pages, then you need to provide a
> suitable ->confirm() hook that can wait on this IO to complete if
> needed. ->map() and ->unmap() can typically use the generic functions,
> ditto ->release(). You can implement ->steal() easily if you use the
> method of dynamically allocating pages for each IO instead of reusing
> them.
>
> So it should not be very hard, your best inspiration is likely to be
> found in fs/splice.c itself.
>
>   

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/