Re: [RFC][PATCH 3/5] check files for checkpointability

Serge E. Hallyn
2009-02-24T01:10:50Z

Quoting Dave Hansen (dave@linux.vnet.ibm.com):
> On Mon, 2009-02-23 at 17:49 -0600, Serge E. Hallyn wrote:
> > Quoting Dave Hansen (dave@linux.vnet.ibm.com):
> > > Introduce a files_struct counter to indicate whether a particular
> > > file_struct has ever contained a file which can not be
> > > checkpointed. This flag is a one-way trip; once it is set, it may
> > > not be unset.
> > >
> > > We assume at allocation that a new files_struct is clean and may
> > > be checkpointed. However, as soon as it has had its files filled
> > > from its parent's, we check it for real in __scan_files_for_cr().
> > > At that point, we mark it if it contained any uncheckpointable
> > > files.
> > >
> > > We also check each 'struct file' when it is installed in a fd
> > > slot. This way, if anyone open()s or managed to dup() an
> > > unsuppored file, we can catch it.
> >
> > So what is the point of tagging the files_struct counter and
> > making it a one-way trip? Why not just check every file at
> > checkpoint time?
>
> We need both.
>
> This allows us to tell where and when we went wrong. Take a process
> that's been running for a month. After 5 days it did something random
> to keep it from being checkpointed. You're going to have forgotten all
> about it 25 days later. This gives us an opportunity to spit into dmesg
> or just plain log it. It also gives the app some ability to reflect and
> see what its uncheckpointable attributes are.

Hmm. In that case, rather than refuse checkpoint, I prefer that we make
this a footnote in the /proc/$$/checkpointable output.

-serge