Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance

[Andy Lutomirski]

On Fri, Dec 11, 2015 at 1:11 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> Al Viro <viro@xxxxxxxxxxxxxxxxxx> writes:
>
>> On Fri, Dec 11, 2015 at 01:40:40PM -0600, Eric W. Biederman wrote:
>>
>>> +    inode = path.dentry->d_inode;
>>> +    filp->f_path = path;
>>> +    filp->f_inode = inode;
>>> +    filp->f_mapping = inode->i_mapping;
>>> +    path_put(&old);
>>
>> Don't.  You are creating a fairly subtle constraint on what the code in
>> fs/open.c and fs/namei.c can do, for no good reason.  You can bloody
>> well maintain the information you need without that.
>
> There is a good reason.  We can not write a race free version of ptsname
> without it.

As long as this is for new userspace code, would it make sense to just
add a new ioctl to ask "does this ptmx fd match this /dev/pts fd?"

--Andy
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