[RFC][PATCH 0/5] uts namespaces: Introduction

[Serge E. Hallyn]

Introduce utsname namespaces.  Instead of a single system_utsname
containing hostname domainname etc, a process can request it's
copy of the uts info to be cloned.  The data will be copied from
it's original, but any further changes will not be seen by processes
which are not it's children, and vice versa.

This is useful, for instance, for vserver/openvz, which can now clone
a new uts namespace for each new virtual server.

This patchset is based on Kirill Korotaev's Mar 24 submission, taking
comments (in particular from James Morris and Eric Biederman) into
account.

Some performance results are attached.  I was mainly curious whether
it would be worth putting the task_struct->uts_ns pointer inside
a #ifdef CONFIG_UTS_NS.  The result show that leaving it in when
CONFIG_UTS_NS=n has negligable performance impact, so that is the
approach this patch takes.

-serge

Performance testing was done on a 2-cpu hyperthreaded
x86 box with 16G ram.  The following tests were run:
	dbench (20 times, four clients, on reiser fs non-isolated partition)
	tbench (20 times, 5 connections)
	kernbench (20 times)
	reaim (20 times ranging from 1 to 15 users)

They were run on 2.6.17-rc1:
	pristine
	patched, but with !CONFIG_UTS_NS ("disabled")
	patched with CONFIG_UTS_NS=y ("enabled")

All results are presented as means +/- 95% confidence interval.

Dbench results:
pristine:          387.080727 +/- 9.344585
patched disabled:  389.524364 +/- 9.574921
patched enabled:   370.155600 +/- 30.127808

Tbench results:
pristine:         388.940100 +/- 18.095104
patched disabled: 389.173700 +/- 23.658035
patched enabled:  394.333200 +/- 25.813393

Kernbench results:
pristine:          70.317500 +/- 0.210833
patched, disabled: 70.860000 +/- 0.179292
patched, enabled:  70.346500 +/- 0.184784

Reaim results:
pristine:
        Nclients      Mean         95% CI
           1     106080.000000  11327.896029
           3     236057.142000  18205.544810
           5     247867.136000  23536.800062
           7     265370.000000  21284.335743
           9     262969.936000  18225.497529
          11     278256.000000  6230.342816
          13     284288.016000  8924.589388
          15     286987.170000  7881.034658

patched, disabled:
        Nclients      Mean         95% CI
           1     105400.000000  8739.978241
           3     229500.000000  0.000000
           5     252325.176667  16685.663423
           7     265125.000000  6747.777319
           9     271258.645000  11715.635212
          11     280662.608333  7775.229351
          13     277719.706667  8173.390359
          15     278515.421667  10963.211450

patched, enabled:
        Nclients      Mean         95% CI
           1     102000.000000  0.000000
           3     224400.000000  14159.870036
           5     242963.288000  40529.490781
           7     255150.000000  8745.802081
           9     270154.284000  8918.863136
          11     283134.260000  12239.361252
          13     288497.540000  11336.550964
          15     280022.728000  8804.882369

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