RE: [Xen-devel] [PATCH][RESEND]Nvram patch for IA64

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> >> Yes, static good configurations can be made for different guest OS 
> >> (RHEL, SLES, Win 2003, Win Vista). But I am afraid this workaround 
> >> will have potential issue, because we are unable to 
> predict how guest 
> >> OS would use variable.
> > 
> > Is the variable contents the same for all installs of each 
> of the OSes 
> > you list?
> 
> No, different OS has differrent configurations.

But do all installs of the same OS have the same variable contents? That
was the question.
  
> >>> Further, storing it in a file will create compilcations 
> when we move 
> >>> to running qemu in stub domains -- we'll need a way of passing it 
> >>> across xenbus.
> >> 
> >> Could you please elaborate what the "complications" is? Per my 
> >> understanding, even without NVRAM file, qemu in stub domain still 
> >> need to read/write the disk image file.
> > 
> > You won't be able to write stuff to a file directly, you'll need to 
> > use a front/back driver, which is needlessly complicated. xenbus is 
> > definitely the way to go.
> > 
> >> It is also OK to store NVRAM in xenstore, but seems 
> xenstore have no 
> >> capability to store binary data, it can only store 
> null-termincated 
> >> strings.  If we want to directly store EFI variable in xenstore 
> >> instead of sotre NVRAM binary, we need to para-virtualize guest 
> >> firmware GetVariable/Setvariable interface, which is more 
> >> complicated.
> > 
> > You'll have to escape the NULLs. It might be easiest just 
> to store the 
> > hex string.
> > 
> > You don't need to paravirtulize it as qemu can do the trivial 
> > conversion.
> > 
> > Ian
>  
> OK. this should work. Then the only concern is the size of 
> NVRAM. 64KB data is quite large for xenstore. Is it 
> acceptable to xenstore? Maybe qemu need to compress the data 
> first. Usually, most of the NVRAM content is free area, which 
> is continuous byte "0xFF", so compresion can reduce the size 
> significantly.

Break it into 64 byte (128 character) chunks and only populate nodes
that are not all ones.

Ian

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