From: Oliver Neukum <oliver@neukum.org>
To: Stefan Klug <stefan.klug@baslerweb.com>
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
stern@rowland.harvard.edu
Subject: Re: [PATCH][RFC] USB: zerocopy support for usbfs
Date: Wed, 02 Jul 2014 20:58:37 +0200 [thread overview]
Message-ID: <1404327517.10859.3.camel@linux-fkkt.site> (raw)
In-Reply-To: <53B42B14.7010303@baslerweb.com>
On Wed, 2014-07-02 at 17:53 +0200, Stefan Klug wrote:
> Implementation details:
> The patch only touches drivers/usb/core/devio.c.
> In procy_do_submiturb(), it is checked if zerocopy is allowed. This is
> currently a rough
> check which compares the number of required pages to
> ps->dev->bus->sg_tablesize.
It seems to me that the check is per call, so using
multiple calls one could still pin unlimited amounts
of memory.
> I don't know if there is more to check there.
> Then the user memory provided inside the usbdevfs_urb structure is
> pinned to
> physical memory using get_user_pages_fast().
> All the user pages are added to the scatter-gather list and the logic
> continues as before.
How do you enforce the cache coherency rules?
Also you don't have a fall back if get_user_pages_fast()
returns less than requested. It seems to me that than you
ought to fall back buffered IO.
Regards
Oliver
next prev parent reply other threads:[~2014-07-02 19:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-02 15:53 [PATCH][RFC] USB: zerocopy support for usbfs Stefan Klug
2014-07-02 17:55 ` Greg KH
2014-07-03 7:06 ` Stefan Klug
2014-07-02 18:24 ` Alan Stern
2014-07-02 18:49 ` Peter Stuge
2014-07-02 19:31 ` Alan Stern
2014-07-02 19:42 ` Peter Stuge
2014-07-02 20:40 ` Alan Stern
2014-07-03 7:48 ` Stefan Klug
2014-07-03 8:40 ` David Laight
2014-07-03 14:15 ` Alan Stern
2014-07-02 18:58 ` Oliver Neukum [this message]
2014-07-02 19:38 ` Alan Stern
2014-07-03 8:22 ` Stefan Klug
2014-07-04 8:55 ` Oliver Neukum
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