From: Jonathan Wakely <jwakely@redhat.com>
To: libc-coord@lists.openwall.com
Cc: Rich Felker <dalias@libc.org>,
linux-man@vger.kernel.org, musl@lists.openwall.com,
libc-alpha@sourceware.org
Subject: [musl] Re: [libc-coord] Re: regression in man pages for interfaces using loff_t
Date: Fri, 30 Jun 2023 09:02:17 +0100 [thread overview]
Message-ID: <CACb0b4nkLFOi4q=SSBSD_7aH4FRt9H4sRHQz6wF5O-x9PiwnFA@mail.gmail.com> (raw)
In-Reply-To: <8e65a459-a933-38b4-5f82-f7016c107d91@cs.ucla.edu>
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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.
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next prev parent reply other threads:[~2023-06-30 8:02 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-28 17:53 [musl] " Rich Felker
2023-06-28 18:21 ` [musl] " Paul Eggert
2023-06-28 19:15 ` Rich Felker
2023-06-30 7:11 ` Paul Eggert
2023-06-30 8:02 ` Jonathan Wakely [this message]
2023-06-30 8:14 ` [musl] Re: [libc-coord] " Jonathan Wakely
2023-06-30 8:30 ` Sam James
2023-06-30 19:44 ` Paul Eggert
2023-07-02 1:18 ` A. Wilcox
2023-07-02 19:21 ` Paul Eggert
2023-07-03 18:16 ` Jakub Wilk
2023-07-03 21:35 ` Paul Eggert
2023-07-08 17:03 ` Alejandro Colomar
2023-07-09 6:07 ` [musl] [PATCH v4] off64_t: prefer off_t for splice, etc Paul Eggert
2023-07-09 6:16 ` [musl] Re: [libc-coord] " Sam James
2023-07-15 15:08 ` Alejandro Colomar
2023-07-15 18:35 ` Rich Felker
2023-07-15 20:01 ` Paul Eggert
2023-07-16 0:35 ` Alejandro Colomar
2023-07-16 0:39 ` Alejandro Colomar
2023-06-30 23:37 ` [musl] Re: regression in man pages for interfaces using loff_t Rich Felker
2023-07-01 7:24 ` [musl] Re: [libc-coord] " Paul Eggert
2023-07-01 13:36 ` Szabolcs Nagy
2023-07-01 23:02 ` Paul Eggert
2023-07-01 14:32 ` Rich Felker
2023-07-01 18:45 ` Alejandro Colomar
2023-07-01 23:06 ` Paul Eggert
2023-06-28 19:19 ` Szabolcs Nagy
2023-06-28 19:28 ` Rich Felker
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