From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752276AbbDAPRl (ORCPT ); Wed, 1 Apr 2015 11:17:41 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:37833 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056AbbDAPRh convert rfc822-to-8bit (ORCPT ); Wed, 1 Apr 2015 11:17:37 -0400 From: Michal Nazarewicz To: Robert Baldyga , balbi@ti.com Cc: gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Robert Baldyga Subject: Re: [PATCH] usb: gadget: ffs: don't allow to open with O_NONBLOCK flag In-Reply-To: <1427881176-30522-1-git-send-email-r.baldyga@samsung.com> Organization: http://mina86.com/ References: <1427881176-30522-1-git-send-email-r.baldyga@samsung.com> User-Agent: Notmuch/0.19+53~g2e63a09 (http://notmuchmail.org) Emacs/25.0.50.1 (x86_64-unknown-linux-gnu) X-Face: PbkBB1w#)bOqd`iCe"Ds{e+!C7`pkC9a|f)Qo^BMQvy\q5x3?vDQJeN(DS?|-^$uMti[3D*#^_Ts"pU$jBQLq~Ud6iNwAw_r_o_4]|JO?]}P_}Nc&"p#D(ZgUb4uCNPe7~a[DbPG0T~!&c.y$Ur,=N4RT>]dNpd;KFrfMCylc}gc??'U2j,!8%xdD Face: 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 X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 X-Hashcash: 1:20:150401:gregkh@linuxfoundation.org::rfApR825DdwOLcLV:0000000000000000000000000000000000003Ub X-Hashcash: 1:20:150401:balbi@ti.com::CK7V/IdC/eC108Wc:000000Isq X-Hashcash: 1:20:150401:r.baldyga@samsung.com::D6IYql4SrnikF3XG:00000000000000000000000000000000000000000dzL X-Hashcash: 1:20:150401:linux-kernel@vger.kernel.org::UY3SG5XZqHKOtE+9:0000000000000000000000000000000001JIV X-Hashcash: 1:20:150401:r.baldyga@samsung.com::d6HGgigNc1MtV4hx:0000000000000000000000000000000000000000586e X-Hashcash: 1:20:150401:linux-usb@vger.kernel.org::4EZ9eeFOkM6Zq5to:0000000000000000000000000000000000007umr Date: Wed, 01 Apr 2015 17:17:32 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 01 2015, Robert Baldyga 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. ‘can’t’ is a bit strong of a word here though. It can, but in a few cases it doesn’t. 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). I’m 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). > Signed-off-by: Robert Baldyga > --- > drivers/usb/gadget/function/f_fs.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c > index 175c995..1014911 100644 > --- a/drivers/usb/gadget/function/f_fs.c > +++ b/drivers/usb/gadget/function/f_fs.c > @@ -538,6 +538,14 @@ static int ffs_ep0_open(struct inode *inode, struct file *file) > if (unlikely(ffs->state == FFS_CLOSING)) > return -EBUSY; > > + /* > + * We are not supporting 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. > + */ > + if (unlikely(file->f_flags & O_NONBLOCK)) > + return -EWOULDBLOCK; > + > file->private_data = ffs; > ffs_data_opened(ffs); > > @@ -874,6 +882,14 @@ ffs_epfile_open(struct inode *inode, struct file *file) > if (WARN_ON(epfile->ffs->state != FFS_ACTIVE)) > return -ENODEV; > > + /* > + * We are not supporting 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. > + */ > + if (unlikely(file->f_flags & O_NONBLOCK)) > + return -EWOULDBLOCK; > + > file->private_data = epfile; > ffs_data_opened(epfile->ffs); > > -- > 1.9.1 > -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +------ooO--(_)--Ooo--