Re: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)

Daniel Phillips
2001-05-24T17:24:45Z

On Thursday 24 May 2001 02:23, Edgar Toernig wrote:
> Daniel Phillips wrote:
> > > > It's going to be marked 'd', it's a directory, not a file.
> > >
> > > Aha. So you lose the S_ISCHR/BLK attribute.
> >
> > Readdir fills in a directory type, so ls sees it as a directory and
> > does the right thing. On the other hand, we know we're on a device
> > filesystem so we will next open the name as a regular file, and
> > find ISCHR or ISBLK: good.
>
> ??? The kernel may know it, but the app? Or do you really want to
> give different stat data on stat(2) and fstat(2)? These flags are
> currently used by archive/backup prgs. It's a hint that these files
> are not regular files and shouldn't be opened for reading.
> Having a 'd' would mean that they would really try to enter the
> directory and save it's contents. Don't know what happens in this
> case to your "special" files ;-)

I guess that's much like the question 'what happens in proc?'.

Recursively entering the device directory is ok as long as everything
inside it is ok. I tried zipping /proc/bus -r and what I got is what I'd
expect if I'd cat'ed every non-directory entry. This is what I
expected. Maybe it's not right - zipping /proc/kcore is kind of
interesting. Regardless, we are no worse than proc here. In fact,
since we don't anticipate putting an elephant like kcore in as a
device property, we're a little nicer to get along with.

Correct me if I'm wrong, but what we learn from the proc example
is that tarring your whole source tree starting at / is not something
you want to do. Just extend that idea to /dev - however, if you do
it, it will produce pretty reasonable results.

What *won't* happen is, you won't get side effects from opening
your serial ports (you'd have to open them without O_DIRECTORY
to get that) so that seems like a little step forward.

I'm still thinking about some of your other comments.

--
Daniel

--
Daniel