Xen devel - Jun 2008 - [PATCH][TOOLS] libxc: mmap fixes for BSD

Hi!

On BSD, mmap()ing files works on on-disk files but not on
pseudo filesystems like kernfs or procfs.
Therefore, attached patch mmap()s anonymous memory.

Linux equivalents are sysfs and procfs to above BSD''s
pseudo-filesystems.
On Linux, mmap is implemented for sysfs but it is questionable to me
how write operations work since (most) files in sysfs have
static content. So this patch may fix some problems
with a Linux Dom0, too.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>


-- 
AMD Saxony, Dresden, Germany
Operating System Research Center

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   Dr. Hans-R. Deppe, Thomas McCoy


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On 10/6/08 15:09, "Christoph Egger" <Christoph.Egger@amd.com>
wrote:
> On BSD, mmap()ing files works on on-disk files but not on
> pseudo filesystems like kernfs or procfs.
> Therefore, attached patch mmap()s anonymous memory.
> 
> Linux equivalents are sysfs and procfs to above BSD''s
pseudo-filesystems.
> On Linux, mmap is implemented for sysfs but it is questionable to me
> how write operations work since (most) files in sysfs have
> static content. So this patch may fix some problems
> with a Linux Dom0, too.
We can hide special setup in mmap(/proc/xen/privcmd) that is necessary for
later foreign mapping operations. Perhaps xc_map_foreign_ranges() interface
could be changed so that it does the mmap(), then fills in the .va field in
the array of entries that it is passed, and finally return the address it
got from mmap()?

This would make xc_map_foreign_ranges() similar to our other xc_map*()
functions, which all hide the mmap() invocation inside their implementation.

 -- Keir



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On Tuesday 10 June 2008 16:21:56 Keir Fraser wrote:
> On 10/6/08 15:09, "Christoph Egger"
<Christoph.Egger@amd.com> wrote:
> > On BSD, mmap()ing files works on on-disk files but not on
> > pseudo filesystems like kernfs or procfs.
> > Therefore, attached patch mmap()s anonymous memory.
> >
> > Linux equivalents are sysfs and procfs to above BSD''s
pseudo-filesystems.
> > On Linux, mmap is implemented for sysfs but it is questionable to me
> > how write operations work since (most) files in sysfs have
> > static content. So this patch may fix some problems
> > with a Linux Dom0, too.
>
> We can hide special setup in mmap(/proc/xen/privcmd) that is necessary for
> later foreign mapping operations. Perhaps xc_map_foreign_ranges() interface
> could be changed so that it does the mmap(), then fills in the .va field in
> the array of entries that it is passed, and finally return the address it
> got from mmap()?
>
> This would make xc_map_foreign_ranges() similar to our other xc_map*()
> functions, which all hide the mmap() invocation inside their
> implementation.
That''s fine with me.

Christoph

-- 
AMD Saxony, Dresden, Germany
Operating System Research Center

Legal Information:
AMD Saxony Limited Liability Company & Co. KG
Sitz (Geschäftsanschrift):
   Wilschdorfer Landstr. 101, 01109 Dresden, Deutschland
Registergericht Dresden: HRA 4896
vertretungsberechtigter Komplementär:
   AMD Saxony LLC (Sitz Wilmington, Delaware, USA)
Geschäftsführer der AMD Saxony LLC:
   Dr. Hans-R. Deppe, Thomas McCoy


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On Tuesday 10 June 2008 16:21:56 Keir Fraser wrote:
> On 10/6/08 15:09, "Christoph Egger"
<Christoph.Egger@amd.com> wrote:
> > On BSD, mmap()ing files works on on-disk files but not on
> > pseudo filesystems like kernfs or procfs.
> > Therefore, attached patch mmap()s anonymous memory.
> >
> > Linux equivalents are sysfs and procfs to above BSD''s
pseudo-filesystems.
> > On Linux, mmap is implemented for sysfs but it is questionable to me
> > how write operations work since (most) files in sysfs have
> > static content. So this patch may fix some problems
> > with a Linux Dom0, too.
>
> We can hide special setup in mmap(/proc/xen/privcmd) that is necessary for
> later foreign mapping operations. Perhaps xc_map_foreign_ranges() interface
> could be changed so that it does the mmap(), then fills in the .va field in
> the array of entries that it is passed, and finally return the address it
> got from mmap()?
>
> This would make xc_map_foreign_ranges() similar to our other xc_map*()
> functions, which all hide the mmap() invocation inside their
> implementation.
>
>  -- Keir
Here is the patch. This also cleans up and fixes memory leaks in the
error path.

Christoph

-- 
AMD Saxony, Dresden, Germany
Operating System Research Center

Legal Information:
AMD Saxony Limited Liability Company & Co. KG
Sitz (Geschäftsanschrift):
   Wilschdorfer Landstr. 101, 01109 Dresden, Deutschland
Registergericht Dresden: HRA 4896
vertretungsberechtigter Komplementär:
   AMD Saxony LLC (Sitz Wilmington, Delaware, USA)
Geschäftsführer der AMD Saxony LLC:
   Dr. Hans-R. Deppe, Thomas McCoy


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