== VM instructions

=== instructions_type

these are the instructions type


==== fix_checksum_ipv4

This command will fix ipv4 checksum header 

[source,python]
----
{ 
ins_name   :  string ,"fix_checksum_ipv4"  ## this command will recalculate the ipv4 checksum 
pkt_offset : uint16_t, number,      ## the offset into the packet when the ipv4 header is located 
}
----


==== flow_man_simple

This command will allocate and manipulate flow object data 
For example, allocate a flow variable and object from 10.0.0.1-10.0.0.10

[source,python]
----
{ 
ins_name: string, "flow_man_simple" ## increment a flow variable 
flow_varible_name: string "name_of_varible" # internal software will allocate the object for this, the name should be unique
object_size : uint16_t  #size of the variable 1,2,4,8   ( max uint64)
Operation  : "inc","dec","random"  # the command could be inc from min-max start at init 
                                   # decrement 
                                   # random      
split_by_core : true/false      ##do we want to split the range by cores
init_value : number, size of object_size  (max uint64)
min_value  : number, size of object_size (max uint64)
max_value  :  number, size of object_size (max uint64)
}
----

==== write_to_pkt 

This command will copy flow varible into packet offset 

[source,c]
----
tmp_pkt_data = (flow_var +add_value)

if (big_edian){
 (varible_size )pkt[pkt_offset] =swap(tmp_pkt_data);
}
----
        

[source,python]
----
{
ins_name : string , "write_to_pkt" ## 
flow_varible_name : string "name_of_varible" # flow varible value to copy from 
pkt_offset        : uint16_t # the offset into the packet to copy the varible 
add_value         : 0 (size_of_the_varible)# when writing add this value 
big_edian         : bool  default true   # swap varible when copy yo packet 
}
----



=== Examples

=== Examples1

an examples to a programs that change src_ip in specific range for one core
range of src_ip 10.0.0.1-10.0.0.10 start from 10.0.0.7
update ipv4 checksum 
ip offset is in 14

                      offset
[ 6 - dest mac        0
  6 - src  mac        6
  2 network           12
  
  ip[0]               14
  ip[4]               18
  ip[8]-TTL,Protocol  22
  ip[12]-src_ip       26
  ip[12]-dest_ip      30
  
}
 
The program 

[source,python]
----
[ 

{
ins_name : "flow_data_inc" 
flow_varible_name : "src_ip" 
object_size :  1
operaqtion : "inc"
split_by_core : false  # one core 
init_value : 7
min_value  : 1
max_value  : 10 
} ,

{
ins_name : "write_to_pkt" 
flow_varible_name : "src_ip" 
pkt_offset        : 26,
add_value         : 0 ,
big_edian         : true
},

{ 
ins_name : "fix_checksum_ipv4" 
pkt_offset : 14
}

]
----

=== Examples2

an examples to a programs that change src_ip and dest_ip in specific range for one core
range of src_ip  10.0.0.1-10.0.0.10 start from 10.0.0.7
range of dest_ip 48.0.0.1-48.0.0.10 start from 48.0.0.7

update ipv4 checksum 
ip offset is in 14

                      offset
[ 6 - dest mac        0
  6 - src  mac        6
  2 network           12
  
  ip[0]               14
  ip[4]               18
  ip[8]-TTL,Protocol  22
  ip[12]-src_ip       26
  ip[12]-dest_ip      30
  
}

The program 

[source,python]
----

[ 

{
ins_name : "flow_data_inc" 
flow_varible_name : "src_ip" 
object_size :  1
operaqtion : "inc"
split_by_core : false  # one core 
init_value : 7
min_value  : 1
max_value  : 10 
} ,

{
ins_name : "write_to_pkt" 
flow_varible_name : "src_ip" 
pkt_offset        : 26,
add_value         : 0 ,
big_edian         : true
},

{
ins_name : "write_to_pkt" 
flow_varible_name : "src_ip" 
pkt_offset        : 30,
add_value         : 0 ,
big_edian         : true
},


{ 
ins_name : "fix_checksum_ipv4" 
pkt_offset : 14
}
]

----


=== Considerations


==== Control-Plain check

- Verify that packet offset into fix_checksum_ipv4 is less that pkt_size - min_ip_header 
- There is no stream that are orphaned  (not started at startup and nobody call them)

==== Data-Plain  check

- Convert the commands to a VM compress command 
- Allocate flow memory per flow for each stream (currently add the memory in each offset)
- VM runner at startup/ each packet