* [musl] ioctl signature
@ 2024-05-24 17:03 Rafael Ávila de Espíndola
2024-05-24 17:10 ` Rich Felker
0 siblings, 1 reply; 2+ messages in thread
From: Rafael Ávila de Espíndola @ 2024-05-24 17:03 UTC (permalink / raw)
To: musl
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, ...);
Thanks,
Rafael
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [musl] ioctl signature
2024-05-24 17:03 [musl] ioctl signature Rafael Ávila de Espíndola
@ 2024-05-24 17:10 ` Rich Felker
0 siblings, 0 replies; 2+ messages in thread
From: Rich Felker @ 2024-05-24 17:10 UTC (permalink / raw)
To: Rafael Ávila de Espíndola; +Cc: musl
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which is obsolete but the relevant historical standard.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
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