Re: fcntl(F_GETPATH) support

[Mateusz Guzik <mjguzik%gmail.com@localhost>]

On 9/15/19, Mateusz Guzik <mjguzik%gmail.com@localhost> wrote:
> On 9/14/19, Christos Zoulas <christos%zoulas.com@localhost> wrote:
>>
>> Comments?
>>
>> +	error = vnode_to_path(kpath, MAXPATHLEN, fp->f_vnode, l, l->l_proc);
>
> What motivates this change?
>
> I think it is a little problematic in that namecache resolution is not
> guaranteed to work. If the consumer does not check for failure or fallback
> to something else the user is going to experience "once in the blue moon"
> failures.
>
> For example clang likes to get full paths to names. On Linux it can
> trivially do it thanks to dentry cache. On other systems there is a
> compilation check for F_GETPATH. If none of this is present it goes for
> realpath, which is slover but basically works. If F_GETPATH is present,
> it is always used and there is no fallback if it fails. Then you risk
> setting yourself up for a weird compilation failure, which may not even
> repeat itself after you retry.
>
> All in all I don't think this should be added unless namecache becomes
> reliable. The above reasoning is why I did not add it to FreeBSD.
>

Now that I wrote this I suspect a kernel-based realpath could do the
trick here. Will have to take a closer look.

-- 
Mateusz Guzik <mjguzik gmail.com>