It seems that the documents need to be updated to reflect the change in ccf810c
The document says that there is a module option called inplace_data_updates.
* inplace_data_updates: Update data in place rather than with COW (default: 0)
This option does not exist in the code and CoW is not enabled by default:
module_param (measure_timing , int , 0444 );
MODULE_PARM_DESC (measure_timing , "Timing measurement" );
module_param (metadata_csum , int , 0444 );
MODULE_PARM_DESC (metadata_csum , "Protect metadata structures with replication and checksums" );
module_param (wprotect , int , 0444 );
MODULE_PARM_DESC (wprotect , "Write-protect pmem region and use CR0.WP to allow updates" );
module_param (data_csum , int , 0444 );
MODULE_PARM_DESC (data_csum , "Detect corruption of data pages using checksum" );
module_param (data_parity , int , 0444 );
MODULE_PARM_DESC (data_parity , "Protect file data using RAID-5 style parity." );
module_param (dram_struct_csum , int , 0444 );
MODULE_PARM_DESC (dram_struct_csum , "Protect key DRAM data structures with checksums" );
module_param (nova_dbgmask , int , 0444 );
MODULE_PARM_DESC (nova_dbgmask , "Control debugging output" );
In order to enable CoW, one needs to mount with option -o data_cow, and the message nova: Enable copy-on-write updates should be printed to dmesg
case Opt_data_cow :
set_opt (sbi -> s_mount_opt , DATA_COW );
nova_info ("Enable copy-on-write updates\n" );
break ;
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