[Skiboot] [PATCH] external/mambo: support mambo COW mode for PMEM disk

[Michael Neuling]

On Tue, 2020-02-18 at 14:16 -0600, Aaron Sawdey wrote:
> I've added support in mambo's "memory mmap" command to have a "cow" mode
> which just uses MAP_PRIVATE instead of MAP_SHARED on the file so that writes
> to the memory region are not sent back to the file. This allows multiple
> mambo instances to share the same filesystem image.
> 
> This is implemented by having a PMEM_MODES environment variable. If this
> is set, it is expected to contain a comma separated list of modes (rw or cow)
> for the list of files in PMEM_DISK. If there are fewer modes than files, the
> remaining files default to "rw".

I'm not a big fan of the COW name. It suggests the writes are going somewhere. I
realise this is the name used in mambo, but I'm not super keen on it. "PRIVATE"
might be a better name.

Can we call this (singular) PMEM_MODE since we have PMEM_DISK?

Can you also include an example ie

   export PMEM_DISK="mydisk1, mydisk2"
   export PMEM_MODE="rw, cow"

   Other than that, the code looks good.

   Mikey

   > 
> Thanks,
>     Aaron
> 
> 
> Signed-off-by: Aaron Sawdey <acsawdey at linux.ibm.com>
> diff --git a/external/mambo/skiboot.tcl b/external/mambo/skiboot.tcl
> index 8d1cfc66..07c38ab2 100644
> --- a/external/mambo/skiboot.tcl
> +++ b/external/mambo/skiboot.tcl
> @@ -300,20 +300,31 @@ set pmem_sizes ""
>  if { [info exists env(PMEM_VOLATILE)] } {
>      set pmem_sizes [split $env(PMEM_VOLATILE) ","]
>  }
> +set pmem_modes ""
> +if { [info exists env(PMEM_MODES)] } {
> +    set pmem_modes [split $env(PMEM_MODES) ","]
> +}
>  set pmem_root [mysim of addchild $root_node "pmem" ""]
>  mysim of addprop $pmem_root int "#address-cells" 2
>  mysim of addprop $pmem_root int "#size-cells" 2
>  mysim of addprop $pmem_root empty "ranges" ""
>  # Start above where XICS normally is at 0x1A0000000000
>  set pmem_start [expr 0x20000000000]
> +set pmem_file_ix 0
>  foreach pmem_file $pmem_files { # PMEM_DISK
>      set pmem_file [string trim $pmem_file]
>      set pmem_size [file size $pmem_file]
> -    if {[catch {mysim memory mmap $pmem_start $pmem_size $pmem_file rw}]} {
> +    if { [expr [llength $pmem_modes] > $pmem_file_ix] } {
> +	set pmem_mode [lindex $pmem_modes $pmem_file_ix]
> +    } else {
> +	set pmem_mode "rw"
> +    }
> +    if {[catch {mysim memory mmap $pmem_start $pmem_size $pmem_file
> $pmem_mode}]} {
>  	puts "ERROR: pmem: 'mysim mmap' command needs newer mambo"
>  	exit
>      }
>      set pmem_start [pmem_node_add $pmem_root $pmem_start $pmem_size]
> +    set pmem_file_ix [expr $pmem_file_ix + 1]
>  }
>  foreach pmem_size $pmem_sizes { # PMEM_VOLATILE
>      set pmem_start [pmem_node_add $pmem_root $pmem_start $pmem_size]
>