Help converting C code (i2c-dev)

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OK. I have the whole i2c-dev.c converted to Julia. I am having problems with how to define the ccall (again). I’ve been to the Calling C and Fortran documentation and there are no examples of how to pass a struct. Can you help again? I’m sorry to be so ignorant on this stuff.

Here’s the C Code:

#define I2C_SMBUS_BLOCK_MAX	32	/* As specified in SMBus standard */
#define I2C_SMBUS_I2C_BLOCK_MAX	32	/* Not specified but we use same structure */
union i2c_smbus_data {
	__u8 byte;
	__u16 word;
	__u8 block[I2C_SMBUS_BLOCK_MAX + 2]; /* block[0] is used for length */
	                                            /* and one more for PEC */
};

/* This is the structure as used in the I2C_SMBUS ioctl call */
struct i2c_smbus_ioctl_data {
	__u8 read_write;
	__u8 command;
	__u32 size;
	union i2c_smbus_data *data;
};

static inline __s32 i2c_smbus_access(int file, char read_write, __u8 command,
                                     int size, union i2c_smbus_data *data)
{
	struct i2c_smbus_ioctl_data args;

	args.read_write = read_write;
	args.command = command;
	args.size = size;
	args.data = data;
	return ioctl(file,I2C_SMBUS,&args);
}

Here’s the Julia code. I figured i2c_smbus_data can just become a data::Vector{UInt8} and I’ll put/get the values appropriately (something like data[1] becomes byte, data[1] and data[2] become a word [with some bit shifting], and data[1:n] becomes block).

# This is the structure as used in the I2C_SMBUS ioctl call 
mutable struct i2c_smbus_ioctl_data 
	read_write::UInt8
	command::UInt8
	size::UInt32
	data::Vector{UInt8}
end

function i2c_smbus_access(file::Int32, read_write::UInt8, command::UInt8,
                                     size::Int32, data::Vector{UInt8})
	args = i2c_smbus_ioctl_data(read_write, command, size, data)

	#args.read_write = read_write
	#args.command = command
	#args.size = size
	#args.data = data
	
	ret::Int32 = ccall((:ioctl, "libc"), Int32, (Int32, UInt16, i2c_smbus_ioctl_data), file, I2C_SMBUS, args)
	return ret
end