Re: Migration of kernel interfaces to seq_files breaks pread() consumers

[Alexey Dobriyan <adobriyan@gmail.com>]

On Sat, Jan 24, 2009 at 06:19:24PM -0800, Andrew Morton wrote:
> On Fri, 16 Jan 2009 23:51:35 -0800 (PST) Paul Turner <pjt@google.com> wrote:
> 
> > 
> > (Specifically) Several interfaces under /proc have been migrated to use 
> > seq_files.  This was previously observed to be a problem with VMware's 
> > reading of /proc/uptime.  We're now running into the same problem on  
> > /proc/<pid>/stat; we have many consumers performing preads on this 
> > interface which break under new kernels.
> > 
> > Reverting these migrations presents other problems and doesn't scale with 
> > everyones' pet dependencies over an abi that's been
> > broken :(
> 
> We changed userspace-visible behaviour and broke real applications. 
> This is a serious matter.  So serious in fact that your report has
> languished without reply for a week.
> 
> Reverting those changes until we have a suitable reimplementation which
> doesn't bust userspace is 100% justifiable.
> 
> In which kernel versions is this regression present?
> 
> What would a revert look like?  Big and ugly or small and simple?  Do
> the original commits (which were they?) still revert OK?

This is bug http://bugzilla.kernel.org/show_bug.cgi?id=11856
Some of us think what to do here.

Original patch not revertable as is.