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=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_MSPIKE_H2, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 4233 invoked from network); 15 Aug 2022 18:31:51 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 15 Aug 2022 18:31:51 -0000 Received: (qmail 19481 invoked by uid 550); 15 Aug 2022 18:31:49 -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 18423 invoked from network); 15 Aug 2022 18:31:48 -0000 X-Virus-Scanned: SPAM Filter at disroot.org Mime-Version: 1.0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=disroot.org; s=mail; t=1660588295; bh=zrmbZ3KpfFWhJg09zW+ndWTU/8TdCsLShB3VYHn+8UE=; h=Date:Subject:From:To:References:In-Reply-To; b=iQ0JZLO7t9G4LPmlPsIqN8EzQmwSq2ybv42/CIzy8zNduzUoQmomI0DNsiq3/fxW7 HjOytf2gdRvoHpjlsSIwvPJnwW2mlJBctagLJa/O0JCcJ0xhsn4Q/XLmzhDdJhTPLQ DN65jJidhhRYWCqQ30AxREhgYR/bUlZDrXsqOIRrJmLR11JS7/y9JkJOVG+LKI9M1I zYpNOTVYC9pVBemiRXuQvRlhObPrDM6s7yKLoVWrA5DYO09EQ1jCCmI72kde9PUyhC h/RtKXhAyUvgrgDwhRbM/CGHlZqC/+P+suO2Th+2B6v+heks8Fq8YXSRGkqWl0iBHZ 5czQuELVzMblw== Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 15 Aug 2022 15:31:30 -0300 Message-Id: From: =?utf-8?q?=C3=89rico_Nogueira?= To: References: <20220815175021.16659-1-ericonr@disroot.org> <20220815175425.GX7074@brightrain.aerifal.cx> <20220815181608.GY7074@brightrain.aerifal.cx> In-Reply-To: <20220815181608.GY7074@brightrain.aerifal.cx> Subject: Re: [musl] [PATCH] remove extraneous syscall from fopen(3) On Mon Aug 15, 2022 at 3:16 PM -03, Rich Felker wrote: > On Mon, Aug 15, 2022 at 02:58:40PM -0300, =C3=89rico 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, =C3=89rico 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(-) > > > >=20 > > > > 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) > > > > =20 > > > > fd =3D sys_open(filename, flags, 0666); > > > > if (fd < 0) return 0; > > > > - if (flags & O_CLOEXEC) > > > > - __syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC); > > > > =20 > > > > f =3D __fdopen(fd, mode); > > > > if (f) return f; > > > > --=20 > > > > 2.37.2 > > > > > > See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0 > >=20 > > 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. On some level, unless someone inherited a file descriptor or something similar, I'd expect them to have used O_CLOEXEC if they are also using "e" in mode. So hopefully this is not as much of a concern. And I don't think fdopen setting the close-on-exec flag is behavior users can rely on, seeing as glibc doesn't take "e" into account in their fdopen implementation. > 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? >From what testing I have done, a fcntl() call is essentially free, at least when compared to the cost of open(). This commit was intended only as cleanup. > > Rich