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SubjectRe: [RFC][PATCH 8/8] check files for checkpointability
On Mon, 2 Mar 2009 07:37:54 -0600
"Serge E. Hallyn" <serue@us.ibm.com> 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.
> >
> > Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
>
> So on a practical note, Ingo's scheme appears to be paying off. In
> order for any program's files_struct to be checkpointable right now,
> it must be statically compiled, else ld.so (I assume) looks up
> /proc/$$/status. So since proc is not checkpointable, the result
> is irreversibly non-checkpointable.
>
> So... does it make sense to mark proc as checkpointable? Do we
> reasonably assume that the same procfile will be available at
> restart?

With respect to /proc/$x/* where $x is the pid the restarted task wants,
is that not a chicken-and-egg problem?

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