From mboxrd@z Thu Jan 1 00:00:00 1970 From: Changli Gao Subject: Re: [PATCH v2 3/4]: sendfile: remove flags paramter of do_splice_direct() Date: Sun, 30 May 2010 07:58:30 +0800 Message-ID: References: <1274885054-15698-1-git-send-email-xiaosuo@gmail.com> <1275150019.22648.615.camel@gandalf.stny.rr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Miklos Szeredi , axboe@kernel.dk, Al Viro , mszeredi@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Eric Dumazet , Frederic Weisbecker , Ingo Molnar To: rostedt@goodmis.org Return-path: Received: from mail-pz0-f204.google.com ([209.85.222.204]:54819 "EHLO mail-pz0-f204.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756794Ab0E2X6u convert rfc822-to-8bit (ORCPT ); Sat, 29 May 2010 19:58:50 -0400 In-Reply-To: <1275150019.22648.615.camel@gandalf.stny.rr.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sun, May 30, 2010 at 12:20 AM, Steven Rostedt = wrote: > [ Removed matthew@wil.cx since I'm getting errors in sending to that = address ] > > > On Sat, 2010-05-29 at 09:59 +0800, Changli Gao wrote: >> On Fri, May 28, 2010 at 6:06 PM, Changli Gao wro= te: >> > On Fri, May 28, 2010 at 5:40 PM, Miklos Szeredi wrote: >> >> On Wed, 26 May 2010, Changli Gao wrote: >> >>> remove flags paramter of do_splice_direct(). >> >>> >> >>> the flags parameter of do_splice_direct() doesn't mean non-block= read of >> >>> in file, >> >> >> >> Actually, it does. =C2=A0Look at the SPLICE_F_NONBLOCK usage in >> >> __generic_splice_file_read(). >> >> >> > >> > Oh, I checked the code again. You're right. However, why don't we >> > check the flags of in file instead in __generic_file_splice_read()= ? >> > >> >> I am afraid that __generic_file_splice_read() should not use SPLICE_= =46_NONBLOCK. >> >> Here is the comment from the commit 42324c62704365d6a3e89138dea55909= d2f26afe : >> >> <> Linus introduced =C2=A0SPLICE_F_NONBLOCK in commit >> 29e350944fdc2dfca102500790d8ad6d6ff4f69d >> (splice: add SPLICE_F_NONBLOCK flag ) >> >> =C2=A0 It doesn't make the splice itself necessarily nonblocking (be= cause the >> =C2=A0 actual file descriptors that are spliced from/to may block un= less they >> =C2=A0 have the O_NONBLOCK flag set), but it makes the splice pipe o= perations >> =C2=A0 nonblocking. >> >> Linus intention was clear : let SPLICE_F_NONBLOCK control the splice >> pipe mode only >> EOF >> >> And I have greped the whole code: >> > > >> kernel/trace/trace.c: =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (flags &= SPLICE_F_NONBLOCK) >> >> besides the __generic_file_splice_read(), there are two users: relay >> and trace. I believe they all misuse this flag. >> > > > The trace splice never blocks anyway. Since we have no good method to > wake up a waiter. That is, we never know if it is safe to call wakeup= , > because a tracepoint may be in a section where the rq lock is held. > > The only thing that passing SPLICE_F_NONBLOCK does in that code is to > return -EAGAIN when there is nothing in the buffer. Otherwise, it > returns 0. > But why not use (file->f_flags & O_NONBLOCK) instead, as tracing_splice_read_pipe() does? --=20 Regards=EF=BC=8C Changli Gao(xiaosuo@gmail.com) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html