From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_MSPIKE_H2,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 2496 invoked from network); 15 Aug 2022 18:16:26 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 15 Aug 2022 18:16:26 -0000 Received: (qmail 7793 invoked by uid 550); 15 Aug 2022 18:16:23 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 7755 invoked from network); 15 Aug 2022 18:16:22 -0000 Date: Mon, 15 Aug 2022 14:16:09 -0400 From: Rich Felker To: =?utf-8?B?w4lyaWNv?= Nogueira Cc: musl@lists.openwall.com Message-ID: <20220815181608.GY7074@brightrain.aerifal.cx> References: <20220815175021.16659-1-ericonr@disroot.org> <20220815175425.GX7074@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [PATCH] remove extraneous syscall from fopen(3) On Mon, Aug 15, 2022 at 02:58:40PM -0300, Érico Nogueira wrote: > On Mon Aug 15, 2022 at 2:54 PM -03, Rich Felker wrote: > > On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote: > > > the __fdopen() call afterwards will set the close-on-exec flag with the > > > same syscall if "e" was specified in mode > > > --- > > > src/stdio/fopen.c | 2 -- > > > 1 file changed, 2 deletions(-) > > > > > > diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c > > > index e1b91e12..22b72edf 100644 > > > --- a/src/stdio/fopen.c > > > +++ b/src/stdio/fopen.c > > > @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode) > > > > > > fd = sys_open(filename, flags, 0666); > > > if (fd < 0) return 0; > > > - if (flags & O_CLOEXEC) > > > - __syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC); > > > > > > f = __fdopen(fd, mode); > > > if (f) return f; > > > -- > > > 2.37.2 > > > > See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0 > > If the relevant part of that commit is that the flag is added > immediately after, would moving the SYS_fcntl call in __fdopen to the > top of the functon be acceptable? Oh, I missed that it also happens in __fdopen from the 'e' being present, and misunderstood your patch as just removing the fallback entirely. No, it's not acceptable to move the fcntl in __fdopen above the malloc because it would make fdopen modify the fd status on failure. I guess it's questionable whether we care "how soon" after the open it happens -- either way this is not a thread-safe fallback precluding fd leak on old/broken kernels. But since malloc may be application-provided, failure to set it before the malloc like we're doing now would be a "worse behavior" in some sense, exposing the incorrect fd state to a non-multithreaded application. So I'm not sure if it's a good idea to change this or not. Do you have reason to believe it's affecting performance in real-world usage? Rich