On Fri, Dec 11, 2015 at 2:18 PM, H. Peter Anvin <h...@zytor.com> wrote:
> On 12/11/15 14:12, Andy Lutomirski wrote:
>>>
>>> For the newinstance case st_dev should match between the master and the
>>> slave. Unfortunately this is not the case for a legacy ptmx, as a
>>> stat() on the master descriptor still returns the st_dev, st_rdev, and
>>> st_ino for the ptmx device node.
>>
>> Sure, but I'm not talking about stat. I'm saying that we could add a
>> new ioctl that works on any ptmx fd (/dev/ptmx or /dev/pts/ptmx) that
>> answers the question "does this ptmx logically belong to the given
>> devpts filesystem".
>>
>> Since it's not stat, we can make it do whatever we want, including
>> following a link to the devpts instance that isn't f_path or f_inode.
>>
>
> Sure. My thinking, though, was whether or not we can do something that
> works on legacy kernels, and/or is less intrusive than new ioctls.
>
> What is the actual operation we need?
To do the whole shebang at once:
ioctl(ptmx_fd, TIOCWHATEVER, fd_to_devpts_mount);
returns the slave number if fd_to_devpts_mount points to the right
place or an error if not.
ptsname(fd) logically does:
fd_to_devpts_mount = open("/dev/pts", O_RDONLY | O_DIRECTORY);
int n = ioctl(fd, TIOCWHATEVER, fd_to_devpts_mount);
close(fd_to_devpts_mount);
if (n < 0)
return some error;
return "/dev/pts/" + n;
I think that all kinds of variants are possible.
--Andy
>
> -hpa
>
--
Andy Lutomirski
AMA Capital Management, LLC
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