Re: regressions due to 64-bit ext4 directory cookies

On Wed, Feb 13, 2013 at 2:47 PM, Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org> wrote:

> On Wed, Feb 13, 2013 at 05:41:41PM -0500, J. Bruce Fields wrote:
> > > What if we have an ioctl or a process personality flag where a broken
> > > application can tell the file system "I'm broken, please give me a
> > > degraded telldir/seekdir cookie"?  That way we don't penalize programs
> > > that are doing the right thing, while providing some accomodation for
> > > programs who are abusing the telldir cookie.
> >
> > Yeah, if there's a simple way to do that, maybe it would be worth it.
>
> Doing this as an ioctl which gets called right after opendir, i.e
> (ignoring error checking):
>
>       DIR *dir = opendir("/foo/bar/baz");
>       ioctl(dirfd(dir), EXT4_IOC_DEGRADED_READDIR, 1);
>       ...
>
> should be quite easy.  It would be a very ext3/4 specific thing,
> though.


That would work, even though it would be ext3/4 specific. What is the
recommended programmatic way to detect if the file is on ext3/4 -- we would
not want to attempt that blindly on a non-ext3/4 FS as the numerical value
of EXT4_IOC_DEGRADED_READDIR might get interpreted in dangerous ways?

Avati
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