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

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Message-ID: <20090223234911.GB2590@us.ibm.com>
Date:	Mon, 23 Feb 2009 17:49:11 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	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>
Subject: Re: [RFC][PATCH 3/5] check files for checkpointability

Quoting Dave Hansen (dave@...ux.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?

-serge
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