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CLONE_NEWIPC documentation

PATCH Michael Kerrisk 4 participants 7 messages Nov 19, 2008 – Nov 23, 2008 Man-pages: manual pages for Linux -- Sections 2, 3, 4, 5, and 7

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Michael Kerrisk

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#0 lore raw

Kirill, Pavel,

Below is a patch to document the CLONE_NEWIPC flag that was added in 2.6.19.

Could you please review and let me know of improvements or inaccuracies?

Cheers,

Michael

man2/clone.2 +48 -0
@@ -225,6 +224,36 @@ Calls to
 .BR umask (2)
 performed later by one of the processes do not affect the other process.
 .TP
+.BR CLONE_NEWIPC " (since Linux 2.4.19)"
+If
+.B CLONE_NEWIPC
+is set, then create the process in a new IPC namespace.
+If this flag is not set, then (as with
+.BR fork (2)),
+the process is created in the same IPC namespace as
+the calling process.
+This flag is intended for the implementation of control groups.
+
+An IPC namespace consistes of the set of identifiers for
+System V IPC objects.
+(These objects are created using
+.BR msgctl (2),
+.BR semctl (2),
+and
+.BR shmctl (2)).
+Objects created in an IPC namespace are visible to other processes
+that are members of that namespace,
+but are not visible to processes in other IPC namespaces.
+
+Use of this flag requires: a kernel configured with the
+.B CONFIG_SYSVIPC
+and
+.B CONFIG_IPC_NS
+configuration options and that the process be privileged
+.RB ( CAP_SYS_ADMIN ).
+This flag can't be specified in conjunction with
+.BR CLONE_SYSVSEM .
+.TP
 .BR CLONE_NEWNS " (since Linux 2.4.19)"
 Start the child in a new namespace.
 

@@ -729,6 +758,14 @@ were specified in
 .TP
 .B EINVAL
 Both
+.B CLONE_NEWIPC
+and
+.B CLONE_SYSVSEM
+were specified in
+.IR flags .
+.TP
+.B EINVAL
+Both
 .BR CLONE_NEWPID
 and
 .BR CLONE_THREAD

@@ -742,6 +779,16 @@ when a zero value is specified for
 .IR child_stack .
 .TP
 .B EINVAL
+.BR CLONE_NEWIPC
+was specified in
+.IR flags ,
+but the kernel was not configured with the
+.B CONFIG_SYSVIPC
+and
+.BR CONFIG_IPC_NS
+options.
+.TP
+.B EINVAL
 .BR CLONE_NEWPID
 was specified in
 .IR flags ,
#1 lore raw
Quoted 18 lines · Michael Kerrisk

Kirill, Pavel,

Below is a patch to document the CLONE_NEWIPC flag that was added in 2.6.19.

Could you please review and let me know of improvements or inaccuracies?

Cheers,

Michael

man2/clone.2 +0 -0
@@ -225,6 +224,36 @@ Calls to
 .BR umask (2)
 performed later by one of the processes do not affect the other process.
 .TP

man2/clone.2 Calls to · line 236

Quoted 10 lines
man2/clone.2 +9 -0
+.BR CLONE_NEWIPC " (since Linux 2.4.19)"
+If
+.B CLONE_NEWIPC
+is set, then create the process in a new IPC namespace.
+If this flag is not set, then (as with
+.BR fork (2)),
+the process is created in the same IPC namespace as
+the calling process.
 
+This flag is intended for the implementation of control groups.

The above sentence is wrong.

+This flag is intended for the implementation of containers.

Would be correct.

Both control groups and namespaces feed into the user space container concept. Control groups are multiprocess resource limits. Namespaces are affect the mapping from resource name to resource.

What is interesting is you can unshare a sysvipc namespace and still have sysvipc shared memory mapped from another sysvipc namespace.

This is something that needs to be watched for.

Eric
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#2 lore raw
Quoted 9 lines · Eric W. Biederman
Quoted 7 lines · Michael Kerrisk

Kirill, Pavel,

Below is a patch to document the CLONE_NEWIPC flag that was added in 2.6.19.

Could you please review and let me know of improvements or inaccuracies?

I would also add that an interesting effect of the sysvipc namespace is the automatic cleanup of sysvipc objects when the namespace is destroyed.

Thanks

C.
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author
#3 lore raw

Cedric,

Quoted 5 lines · Cedric Le Goater
Quoted 4 lines · Eric W. Biederman
Quoted 2 lines · Michael Kerrisk

Kirill, Pavel,

Quoted 8 lines
Quoted 5 lines
Quoted 5 lines

Below is a patch to document the CLONE_NEWIPC flag that was added in 2.6.19.

Could you please review and let me know of improvements or inaccuracies?

I would also add that an interesting effect of the sysvipc namespace is the automatic cleanup of sysvipc objects when the namespace is destroyed.

And the namespace is destroyed, when the last proces in the namespace terminates, right?

Cheers,

Michael

Signature · 9 lines
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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#4 lore raw
Quoted 11 lines · Michael Kerrisk

Cedric,

Quoted 8 lines · Cedric Le Goater
Quoted 7 lines · Eric W. Biederman
Quoted 5 lines · Michael Kerrisk

Kirill, Pavel,

Below is a patch to document the CLONE_NEWIPC flag that was added in 2.6.19.

Quoted 7 lines
Quoted 4 lines
Quoted 2 lines
Quoted 2 lines

Could you please review and let me know of improvements or inaccuracies?

I would also add that an interesting effect of the sysvipc namespace is the automatic cleanup of sysvipc objects when the namespace is destroyed.

And the namespace is destroyed, when the last proces in the namespace terminates, right?

exactly.

Thanks,

C.
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author
#5 lore raw
Quoted 14 lines · Cedric Le Goater
Quoted 13 lines · Michael Kerrisk

Cedric,

Quoted 10 lines · Cedric Le Goater
Quoted 9 lines · Eric W. Biederman
Quoted 7 lines · Michael Kerrisk

Kirill, Pavel,

Below is a patch to document the CLONE_NEWIPC flag that was added in 2.6.19.

Could you please review and let me know of improvements or inaccuracies?

Quoted 7 lines
Quoted 5 lines
Quoted 2 lines

I would also add that an interesting effect of the sysvipc namespace is the automatic cleanup of sysvipc objects when the namespace is destroyed.

And the namespace is destroyed, when the last proces in the namespace terminates, right?

exactly.

Thanks Cedric. I've added that point to the documentation.

Cheers,

Michael

Signature · 9 lines
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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#6 lore raw
In reply to Eric W. Biederman
Quoted 8 lines · Eric W. Biederman
Quoted 1 line

+This flag is intended for the implementation of control groups.

The above sentence is wrong.

+This flag is intended for the implementation of containers.

Would be correct.

Quoted 8 lines

Both control groups and namespaces feed into the user space container concept. Control groups are multiprocess resource limits. Namespaces are affect the mapping from resource name to resource.

What is interesting is you can unshare a sysvipc namespace and still have sysvipc shared memory mapped from another sysvipc namespace.

This is something that needs to be watched for.

Oh, I see, so please disregard my last msg, it seems Eric was plenty clear.

thanks,
-serge