Re: Bug in man page for CONSOLE_IOCTL(4) - KDGETMODE

Hello Chris

On 07/16/2016 05:11 AM, Chris Gassib wrote:

Description:
The manual entry for KDGETMODE specifies "argp points to a long which
is set to one of the above values." At least on x86_64-bit Fedora24,
the text should probably specify argp is an int (32-bit), rather than
a long (64-bit).

Repo:
Open a file descriptor to the local console, and execute some code like the following:
    long arg = -1;
    if (-1 == ioctl(fd, KDGETMODE, &arg)) { return -1; }
    printf("KDGETMODE: 0x%lx\n", arg);

Now try this version:
    int arg = -1;
    if (-1 == ioctl(fd, KDGETMODE, &arg)) { return -1; }
    printf("KDGETMODE: 0x%x\n", arg);

Result:
The first version gives this result:
KDGETMODE: 0xffffffff00000001

The second version gives this result:
KDGETMODE: 0x1

Expected:
Either documentation incorrect, or the API is. One of them should be
changed so they match, or perhaps the documentation should specify
that it only applies to the 32-bit version.

Reading the source confirms your point, and it's the documentation that
should be fixed. I've made that change. Thanks for the report.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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