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=-1.5 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, HTML_MESSAGE,MAILING_LIST_MULTI,RCVD_IN_DNSWL_LOW,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 11700 invoked from network); 30 Jun 2023 08:02:50 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 30 Jun 2023 08:02:50 -0000 Received: (qmail 13822 invoked by uid 550); 30 Jun 2023 08:02:46 -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 13797 invoked from network); 30 Jun 2023 08:02:45 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688112154; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rNSnjrIDbm6AOV3jeiylUVOUdmdeHjIY8XS75UaagZc=; b=AKYqL37plaO7rZi+XgOtrVrSBAfTXD9+PjcJgmGavz9GVONYBfl0B0X3mERKnzwE55SqRW zDKQeRCvz9BVOkPadYCDLY8vIowTBkQuKGDyWLgE1FbE68mMrk8bzBFputfy2SvuDImJ+M /UJflSEbL8im03A/sh3B/XUSyIvowaY= X-MC-Unique: 6MMoAFxRP7e4sM8S52L5Ig-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688112148; x=1690704148; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=rNSnjrIDbm6AOV3jeiylUVOUdmdeHjIY8XS75UaagZc=; b=bD4ErsHFy13ZbJPXc8+7tuBKyF7gBDghPwcdVzH0rjto0UwbiEh86FvlMxlFAdQlNs 6Ip4uxeYGRwq63D290+aL9fA8SbeCqQqFQPWahcGVbL6lVbfPpmfcPbY2Cau+w8iczV9 ndHVZTFhIVznsPMUO73+14s0DeuWkXM0hXnMg7HVa8Bir/HAPG5nyIP7qs2z/p9wO13f 4Sy0WX0pMtmZ18uCUBoZdcOphAYqaUNJepBQSGe9WTejHRVVLW3g4iGJQRAyJKHowQCp rjlWL1D51JBd++eLV1gGoujFR9bgnDgeZ5FigvpfidtbvdHBuXGsAi5vYXCQfTFAc51e pM3A== X-Gm-Message-State: ABy/qLa72NxxSrfTvNqouXrzM4OthDaouE05WpSeDmyb9nicUX3iFbK3 Ap7Ast0GN2fSKweAzVVrTXo6Wy1UGmD30B6larPDVqc+JX4B+8RxhrCX4RbtEX0+8X2T2M89A++ ab7AqHWraKe0fcrcykcjnoEdlCvIi2sdY8w== X-Received: by 2002:a2e:9599:0:b0:2b6:a841:e686 with SMTP id w25-20020a2e9599000000b002b6a841e686mr1543302ljh.6.1688112148719; Fri, 30 Jun 2023 01:02:28 -0700 (PDT) X-Google-Smtp-Source: APBJJlHhVm34v0fu3sGbA5ZiiKxqDjRFpPP7/SRf0tnasF/NJHkPscrID8MolJJW9Rv68Y69ZwyYpvw0h1rFBBSUDKk= X-Received: by 2002:a2e:9599:0:b0:2b6:a841:e686 with SMTP id w25-20020a2e9599000000b002b6a841e686mr1543287ljh.6.1688112148436; Fri, 30 Jun 2023 01:02:28 -0700 (PDT) MIME-Version: 1.0 References: <20230628175329.GA16113@brightrain.aerifal.cx> <20230628191525.GS20050@brightrain.aerifal.cx> <8e65a459-a933-38b4-5f82-f7016c107d91@cs.ucla.edu> In-Reply-To: <8e65a459-a933-38b4-5f82-f7016c107d91@cs.ucla.edu> From: Jonathan Wakely Date: Fri, 30 Jun 2023 09:02:17 +0100 Message-ID: To: libc-coord@lists.openwall.com Cc: Rich Felker , linux-man@vger.kernel.org, musl@lists.openwall.com, libc-alpha@sourceware.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/alternative; boundary="000000000000f2efdf05ff543cf3" Subject: [musl] Re: [libc-coord] Re: regression in man pages for interfaces using loff_t --000000000000f2efdf05ff543cf3 Content-Type: text/plain; charset="UTF-8" On Fri, 30 Jun 2023 at 08:11, Paul Eggert wrote: > On 2023-06-28 12:15, Rich Felker wrote: > > > There's also the problem that off64_t is "exactly 64-bit" which makes > > it unsuitable as an interface type for cross-platform functions where > > one could imagine the native type being larger (rather horrifying but > > possible). > > Although we won't have files with 2**63 bytes any time soon, this is the > best argument for preferring "loff_t" to "off64_t". > > But come to think of it, it'd be better to document the type simply as > "off_t", with a footnote saying the equivalent of "this assumes that on > 32-bit glibc platforms you compile with -DFILE_OFFSET_BITS=64 like any > sane person would." The intent really is off_t here, and that will > remain true even if off_t ever widens past 64 bits. > > All the apps I know that use the syscalls in question simply pass > values that fit in off_t to these functions, and this will work > regardless of whether these apps are compiled with 64- or (horrors!) > 32-bit off_t. Admittedly the footnote solution would not be perfect, but > it's good enough, and it would sidestep the loff_t vs off64_t confusion. > For APIs like copy_file_range(2) and splice(2) the arguments are loff_t* so you can't just "pass arguments that fit in off_t" to them. You have to get the pointer type correct, because writing 64-bits through a 32-bit off_t would be bad. And in C++ it won't even compile unless you get the pointer types exactly right (C compilers will typically allow the mismatch with just a warning). People miss footnotes. I would really prefer if the signature shown in the man page used a type that will actually compile. If it shows off_t, that won't compile for 32-bit systems without LFS support enabled. --000000000000f2efdf05ff543cf3 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Fri, 30 Jun 2023 at 08:11, Paul Eggert= wrote:
On 2023-06-28 12:15, Rich Felker wrote:

> There's also the problem that off64_t is "exactly 64-bit"= ; which makes
> it unsuitable as an interface type for cross-platform functions where<= br> > one could imagine the native type being larger (rather horrifying but<= br> > possible).

Although we won't have files with 2**63 bytes any time soon, this is th= e
best argument for preferring "loff_t" to "off64_t".

But come to think of it, it'd be better to document the type simply as =
"off_t", with a footnote saying the equivalent of "this assu= mes that on
32-bit glibc platforms you compile with -DFILE_OFFSET_BITS=3D64 like any sane person would." The intent really is off_t here, and that will remain true even if off_t ever widens past 64 bits.

All the apps I know that use the syscalls in question simply pass
values that fit in off_t to these functions, and this will work
regardless of whether these apps are compiled with 64- or (horrors!)
32-bit off_t. Admittedly the footnote solution would not be perfect, but it's good enough, and it would sidestep the loff_t vs off64_t confusion= .

For APIs like copy_file_range(2) and = splice(2) the arguments are loff_t* so you can't just "pass argume= nts that fit in off_t" to them. You have to get the pointer type corre= ct, because writing 64-bits through a 32-bit off_t would be bad. And in C++= it won't even compile unless you get the pointer types exactly right (= C compilers will typically allow the mismatch with just a warning).

People miss footnotes. I would really prefer if the signat= ure shown in the man page used a type that will actually compile. If it sho= ws off_t, that won't compile for 32-bit systems without LFS support ena= bled.

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