On 2013-04-08 16:54, H Hartley Sweeten wrote:
On Friday, April 05, 2013 9:52 PM, Ian Abbott wrote:
On 06/04/13 00:07, H Hartley Sweeten wrote:
The struct file_operations (*read) and (*write) operations expect the
buffer to be a __user space pointer.
Currently the (*write) operations in this driver cause this warning:
warning: incorrect type in argument 2 (different address spaces)
expected char const [noderef] <asn:1>*<noident>
got unsigned char [usertype] *buf
And the (*read) operations cause this warning:
warning: incorrect type in argument 2 (different address spaces)
expected char [noderef] <asn:1>*<noident>
got unsigned char *<noident>
Use __force to cast the buffer to a __user pointer to suppress the
warnings.
The sparse warnings are probably helpful in this case. They indicate
the driver is doing something wrong! Using __force just masks the problem.
Normally I would agree, but in this case I don't think so.
The tty read/write in this driver is not directly initiated by user space and we
don't have a __user buffer to pass to the read/write functions.
I guess the kernel buffers could be copied to __user buffers, use that buffer,
then copy the data back to the kernel buffer, but that seems like unnecessary
overhead.
Take a look at __kernel_write() in fs/read_write.c for a similar example that
is already in the kernel.
Okay, I suppose the set_fs(KERNEL_DS) calls let you pass kernel memory
pointers in place of user memory pointers, so the driver isn't doing
anything wrong, it's just using deep magic.
--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@xxxxxxxxx> )=-
-=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
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