linux-kernel - Re: [PATCH] usb: gadget: ffs: don't allow to open with O

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Message-ID: <xa1tfv8bafec.fsf@mina86.com>
Date:	Tue, 07 Apr 2015 21:48:27 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	David Laight <David.Laight@...LAB.COM>,
	'Robert Baldyga' <r.baldyga@...sung.com>,
	"balbi\@ti.com" <balbi@...com>
Cc:	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: ffs: don't allow to open with O_NONBLOCK flag

> From: Robert Baldyga
>> 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.

On Tue, Apr 07 2015, David Laight wrote:
> Is that really necessary?
> I'm sure there are a lot of device drivers that ignore O_NONBLOCK.

FFS partially supports O_NONBLOCK which may fool people into thinking it
has full support.

epfiles don’t implement poll though so I’m not sure how users would
imagine O_NONBLOCK being used with them.  ep0, on the other hand,
implements poll and (as far as I can see and despite what Robert wrote)
suffers from the same problem so it may be considered a bigger issue.

Overall though, I do agree that we need to consider whether the current
situation is really a serious problem.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
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