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In-Reply-To: <20060429075311.GB1886@kroah.com>
Subject: Re: [PATCH] s390: Hypervisor File System
To: Greg KH <greg@kroah.com>, joel.becker@oracle.com
Cc: akpm@osdl.org, ioe-lkml@rameria.de, joern@wohnheim.fh-wedel.de,
       linux-kernel@vger.kernel.org, mschwid2@de.ibm.com,
       penberg@cs.helsinki.fi
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From: Michael Holzheu <HOLZHEU@de.ibm.com>
Date: Tue, 2 May 2006 15:00:20 +0200
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Hi Greg and Joel,

Greg KH <greg@kroah.com> wrote on 04/29/2006 09:53:11 AM:
> On Fri, Apr 28, 2006 at 11:22:25AM +0200, Michael Holzheu wrote:
> > On zSeries machines there exists an interface which allows the
operating
> > system  to retrieve LPAR hypervisor accounting data. For example, it is
> > possible to get usage data for physical and virtual cpus. In order to
> > provide this information to user space programs, I implemented a new
> > virtual Linux file system named 'hypfs' using the Linux 2.6 libfs
> > framework. The name 'hypfs' stands for 'Hypervisor Filesystem'. All the
> > accounting information is put into different virtual files which can be
> > accessed from user space. All data is represented as ASCII strings.
> >
> > When the file system is mounted the accounting information is retrieved
> > and a file system tree is created with the attribute files containing
> > the cpu information. The content of the files remains unchanged until a
> > new update is made. An update can be triggered from user space through
> > writing 'something' into a special purpose update file.
> >
> > We create the following directory structure:
> >
> > <mount-point>/
> >         update
> >         cpus/
> >                 <cpu-id>
> >                         type
> >                         mgmtime
> >                 <cpu-id>
> >                         ...
> >         hyp/
> >                 type
> >         systems/
> >                 <lpar-name>
> >                         cpus/
> >                                 <cpu-id>
> >                                         type
> >                                         mgmtime
> >                                         cputime
> >                                         onlinetime
> >                                 <cpu-id>
> >                                         ...
> >                 <lpar-name>
> >                         cpus/
> >                                 ...
> >
> > - update: File to trigger update
> > - cpus/: Directory for all physical cpus
> > - cpus/<cpu-id>/: Directory for one physical cpu.
> > - cpus/<cpu-id>/type: Type name of physical zSeries cpu.
> > - cpus/<cpu-id>/mgmtime: Physical-LPAR-management time in microseconds.
> > - hyp/: Directory for hypervisor information
> > - hyp/type: Typ of hypervisor (currently only 'LPAR Hypervisor')
> > - systems/: Directory for all LPARs
> > - systems/<lpar-name>/: Directory for one LPAR.
> > - systems/<lpar-name>/cpus/<cpu-id>/: Directory for the virtual cpus
> > - systems/<lpar-name>/cpus/<cpu-id>/type: Typ of cpu.
> > - systems/<lpar-name>/cpus/<cpu-id>/mgmtime:
> > Accumulated number of microseconds during which a physical
> > CPU was assigned to the logical cpu and the cpu time was
> > consumed by the hypervisor and was not provided to
> > the LPAR (LPAR overhead).
> >
> > - systems/<lpar-name>/cpus/<cpu-id>/cputime:
> > Accumulated number of microseconds during which a physical CPU
> > was assigned to the logical cpu and the cpu time was consumed
> > by the LPAR.
> >
> > - systems/<lpar-name>/cpus/<cpu-id>/onlinetime:
> > Accumulated number of microseconds during which the logical CPU
> > has been online.
> >
> > As mount point for the filesystem /sys/hypervisor is created.
> >
> > The update process is triggered when writing 'something' into the
> > 'update' file at the top level hypfs directory. You can do this e.g.
> > with 'echo 1 > update'. During the update the whole directory structure
> > is deleted and built up again.
>
> This sounds a lot like configfs.  Why not use that instead?
>

After having a deeper look into configfs, I do not understand how
to create a directory tree. Is it somehow possible to create a
directory tree as a result of mkdir? Maybe I missed here
something...

Michael

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