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To: Dave Hansen <haveblue@us.ibm.com>
Cc: Andrew Morton <akpm@osdl.org>, Herbert Poetzl <herbert@13thfloor.at>,
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Subject: Re: [PATCH 0/9] namespaces: Introduction
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From: ebiederm@xmission.com (Eric W. Biederman)
Date: Sat, 20 May 2006 18:48:25 -0600
In-Reply-To: <1148069089.6623.197.camel@localhost.localdomain> (Dave
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Dave Hansen <haveblue@us.ibm.com> writes:

> On Fri, 2006-05-19 at 08:13 -0700, Andrew Morton wrote:
>> snapshot/restart/migration worry me.  If they require complete
>> serialisation of complex kernel data structures then we have a problem,
>> because it means that any time anyone changes such a structure they need to
>> update (and test) the serialisation.
>
> The idea of actually serializing kernel data structures keeps me up at
> night.  This is especially true when we already have some method of
> exporting these structures to userspace.

Serialization of kernel data structures is a thorny issue, that
we are far enough away from that we don't need to tackle just yet.
I do consider it a failure to export/import things properly if you
need to use the same kernel version.

For the short term all that is interesting from a checkpoint/restart/migration
perspective is that you can have multiple instances of global identifiers,
pids, sysvipc ids, etc.

> However, the proc-maps/mmap approach would require new interfaces to be
> implemented.  There are plenty of attributes not currently readily
> visible to userspace like VM_NONLINEAR, or resources which are normally
> inaccessible to userspace like deleted files.  Those would need extended
> user/kernel interfaces.

Deleted files are accessible through /proc/<pid>/fd.

Eric
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