Re: Should we nonblocking open FIFO files in COPY?

On Wed, Dec 27, 2017 at 10:18:03AM +0800, Adam Lee wrote:
> On Tue, Dec 26, 2017 at 11:48:58AM -0800, Robert Haas wrote:
> > On Thu, Dec 21, 2017 at 10:10 PM, Adam Lee <ali(at)pivotal(dot)io> wrote:
> > > I have an issue that COPY from a FIFO, which has no writers, could not be
> > > canceled, because COPY invokes AllocateFile() -> fopen() -> blocking open().
> >
> > Hmm. What about the case where we try to open a plain file that's on
> > an inaccessible filesystem, e.g. due to a disk failure? Allowing
> > cancel to work just for FIFOs would be OK, I guess, but allowing it
> > for other open() calls that hang would be better. I'm not sure if we
> > can make it work that way, but it would be nice if we could.
>
> That is doable, just stat() and check before open().

I think TOCTOU when I read such things.. The data folder is a trusted
environment but any patches doing things like that ought to be careful.
--
Michael