linux-kernel - Re: [RFC][PATCH 8/8] check files for checkpointability

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Message-ID: <20090301170010.GC18867@us.ibm.com>
Date:	Sun, 1 Mar 2009 11:00:10 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...e.hu>,
	containers <containers@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oren Laadan <orenl@...columbia.edu>,
	Alexey Dobriyan <adobriyan@...il.com>, hch@...radead.org
Subject: Re: [RFC][PATCH 8/8] check files for checkpointability

Quoting Sukadev Bhattiprolu (sukadev@...ux.vnet.ibm.com):
> Dave Hansen [dave@...ux.vnet.ibm.com] wrote:
> | 
> | 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.
> 
> Hmm. Why not just copy ->may_checkpoint setting from parent (or old)
> files_struct ? If parent is not checkpointable, then child won't be
> and vice-versa - no ?

No.  We don't clear the files_struct checkpointable flag when an
uncheckpointable file is closed.  But if the parent has closed
all uncheckpointable files before forking, then the child can
be started with a checkpointable files_struct.

Otherwise it wouldn't just be the task which has a one-way trip to
uncheckpointability, but process trees, and - assuming init does
anything uncheckpointable at all - the whole system :)

-serge
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