From: David Laight <David.Laight@ACULAB.COM>
To: "'Robert Baldyga'" <r.baldyga@samsung.com>,
Michal Nazarewicz <mina86@mina86.com>,
"balbi@ti.com" <balbi@ti.com>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] usb: gadget: ffs: don't allow to open with O_NONBLOCK flag
Date: Tue, 7 Apr 2015 16:52:56 +0000 [thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB15BBA@AcuExch.aculab.com> (raw)
In-Reply-To: <551E2FBF.5070503@samsung.com>
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From: Robert Baldyga
> Hi Michal,
>
> On 04/01/2015 05:17 PM, Michal Nazarewicz wrote:
> > On Wed, Apr 01 2015, Robert Baldyga <r.baldyga@samsung.com> wrote:
> >> FunctionFS can't support O_NONBLOCK because read/write operatons are
> >> directly translated into USB requests which are asynchoronous, so we
> >> can't know how long we will have to wait for request completion. For
> >> this reason in case of open with O_NONBLOCK flag we return
> >> -EWOULDBLOCK.
> >
> > cant is a bit strong of a word here though. It can, but in a few
> > cases it doesnt.
> >
> > It kinda saddens me that this undoes all the lines of code that were put
> > into the file to support O_NONBLOCK (e.g. FFS_NO_SETUP path of
> > ffs_ep0_read).
> >
> > Im also worried this may break existing applications which, for better
> > or worse, open the file with O_NONBLOCK.
> >
> > Most importantly though, this does not stop users from using fcntl to
> > set O_NONBLOCK, so if you really want to stop O_NONBLOCK from being set,
> > that path should be checked as well (if possible).
>
> I want rather to inform users that non-blocking i/o wouldn't work for
> epfiles. Indeed we can handle O_NONBLOCK for ep0 (for the same reason we
> can have poll), but for other epfiles there is no way to check if
> read/write operation can end up in short time. Everything is up to host.
Is that really necessary?
I'm sure there are a lot of device drivers that ignore O_NONBLOCK.
David
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next prev parent reply other threads:[~2015-04-07 16:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-01 9:39 [PATCH] usb: gadget: ffs: don't allow to open with O_NONBLOCK flag Robert Baldyga
2015-04-01 15:17 ` Michal Nazarewicz
2015-04-03 6:14 ` Robert Baldyga
2015-04-07 13:44 ` Michal Nazarewicz
2015-04-07 16:52 ` David Laight [this message]
2015-04-07 19:48 ` Michal Nazarewicz
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