Message data

[danielkucera]

I'm trying to get message data but I'm getting segfaults:

        if (cmd == RES1):
            print("1 SPI_IOC_MESSAGE")
            print("struct addr", data)
            msg = spi_ioc_transfer.from_address(data)
            data_len = int(msg.len)
            tx_buf_add = int(msg.tx_buf)
            print("tx_buf addr", tx_buf_add)
            print("data_len", data_len)
            tx_buf = (ctypes.c_ubyte).from_address(tx_buf_add)
            print(tx_buf)
#            print(''.join([i for i in tx_buf]))
            return msg.len
        if (cmd == RES2):

results in:

DEBUG:fuse.log-mixin:-> ioctl / (1075866368L, 140722147878816, 1L, 0L, 139711975837784)
1075866368
1 SPI_IOC_MESSAGE
struct addr 139711975837784
tx_buf addr 140722147878848
data_len 38
Segmentation fault (core dumped)

data_len is correct but the tx_buf address is very strange.
Can you help?

[danielkucera]

Ok, I've found the reason: tx_buf belongs to sending app address space so accessing it from different userspace process gives segfault. It is only possible to access it from kernel. Or is there another way?

[danielkucera]

In kernel they use copy_from_user:
https://github.com/torvalds/linux/blob/a86f69d3349569a610eb9ff3b9e4bd1c40fe62f2/drivers/spi/spidev.c#L257