From: Rich Felker <dalias@libc.org>
To: "Rafael Ávila de Espíndola" <rafael@espindo.la>
Cc: musl@lists.openwall.com
Subject: Re: [musl] ioctl signature
Date: Fri, 24 May 2024 13:10:18 -0400 [thread overview]
Message-ID: <20240524171018.GE10433@brightrain.aerifal.cx> (raw)
In-Reply-To: <87v833cfb4.fsf@espindo.la>
On Fri, May 24, 2024 at 05:03:59PM +0000, Rafael Ávila de Espíndola wrote:
> The signature of ioctl in musl is
>
> int ioctl (int, int, ...);
>
> In glibc it is
>
> int ioctl(int fd, unsigned long request, ...);
>
> The requests are always 32 bits, and the most significant bit is used to
> indicated that this ioctl is a read operation. This means that some
> constants are negative numbers if using an int. I have noticed this
> because rust's interface to libc matches the system libc implementation,
> and in alpine I got an error for a literal out of range for
> 0xc0104801. I don't know if a C compiler would produce a warning, but
> that seems somewhat reasonable.
>
> Should the declaration be changed to use an unsigned request?:
>
> int ioctl (int, unsigned int, ...);
The declaration matches the POSIX definition of the ioctl interface,
which is obsolete but the relevant historical standard. From a C
standpoint it doesn't really matter whether the argument is signed or
unsigned since either way the value round-trips right.
I think we explored trying to make the constants come out as signed to
match the interface, but there were reasons that didn't work well
either.
Rich
prev parent reply other threads:[~2024-05-24 17:10 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-24 17:03 Rafael Ávila de Espíndola
2024-05-24 17:10 ` Rich Felker [this message]
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