external/mambo: support mambo COW mode for PMEM disk

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".

Signed-off-by: Aaron Sawdey <acsawdey@linux.ibm.com>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

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]