Transparent ioctls

The third argument of the transparent ioctl is a pointer to the data in user space to be copied in or out.

This address is remapped properly by the ioctl system call. The streams driver or module passes M_COPYIN or M_COPYOUT messages to the stream head and the stream head calls the copyin or copyout subroutines.

If the third argument of the ioctl subroutine points to a structure that contains a pointer (for example, ptr64) or long, remapping is solved by a new structure, copyreq64, which contains a 64-bit user space pointer. If the message block flag is set to MSG64BIT, the driver or module will pass M_COPYIN64 or M_COPYOUT64 to copy in or out a pointer within a structure. In this case, the stream head will call copyin64 or copyout64 to move the data into or out of the user address space, respectively.

struct copyreq64 {
              int     cq_cmd;         /* command type == ioc_cmd */
              cred_t *cq_cr;          /* pointer to full credentials*/
              int     cq_id;          /* ioctl id == ioc_id */
              ioc_pad cq_ad;          /* addr to copy data to/from */
              uint    cq_size;        /* number of bytes to copy */
              int     cq_flag;        /* reserved */
              mblk_t *cq_private;     /* module's private state info*/
              ptr64   cq_addr64;      /* 64-bit address */
              long    cq_filler[2];   /* reserved */
              };

The cq_addr64 field is added in the above structure and the size of the cq_filler is reduced, so overall size remains same. The driver or module first determines whether the MSG64BIT flag is set and, if so, stores the user-space 64-bit address in the cq_addr64 field.