This function passes a command-name and argument to an ENGINE. The cmd_name
is converted to a command number and the control command is called using
'arg' as an argument (unless the ENGINE doesn't support such a command, in
which case no control command is called). The command is checked for input
flags, and if necessary the argument will be converted to a numeric value. If
cmd_optional is non-zero, then if the ENGINE doesn't support the given
cmd_name the return value will be success anyway. This function is intended
for applications to use so that users (or config files) can supply
engine-specific config data to the ENGINE at run-time to control behaviour of
specific engines. As such, it shouldn't be used for calling ENGINE_ctrl()
functions that return data, deal with binary data, or that are otherwise
supposed to be used directly through ENGINE_ctrl() in application code. Any
"return" data from an ENGINE_ctrl() operation in this function will be lost -
the return value is interpreted as failure if the return value is zero,
success otherwise, and this function returns a boolean value as a result. In
other words, vendors of 'ENGINE'-enabled devices should write ENGINE
implementations with parameterisations that work in this scheme, so that
compliant ENGINE-based applications can work consistently with the same
configuration for the same ENGINE-enabled devices, across applications.
This function passes a command-name and argument to an ENGINE. The cmd_name is converted to a command number and the control command is called using 'arg' as an argument (unless the ENGINE doesn't support such a command, in which case no control command is called). The command is checked for input flags, and if necessary the argument will be converted to a numeric value. If cmd_optional is non-zero, then if the ENGINE doesn't support the given cmd_name the return value will be success anyway. This function is intended for applications to use so that users (or config files) can supply engine-specific config data to the ENGINE at run-time to control behaviour of specific engines. As such, it shouldn't be used for calling ENGINE_ctrl() functions that return data, deal with binary data, or that are otherwise supposed to be used directly through ENGINE_ctrl() in application code. Any "return" data from an ENGINE_ctrl() operation in this function will be lost - the return value is interpreted as failure if the return value is zero, success otherwise, and this function returns a boolean value as a result. In other words, vendors of 'ENGINE'-enabled devices should write ENGINE implementations with parameterisations that work in this scheme, so that compliant ENGINE-based applications can work consistently with the same configuration for the same ENGINE-enabled devices, across applications.