linux-user: Add support for getting/setting RTC periodic interrupt and epoch using...

linux-user: Add support for getting/setting RTC periodic interrupt and epoch using ioctls

This patch implements functionalities of following ioctls:

RTC_IRQP_READ, RTC_IRQP_SET - Getting/Setting IRQ rate

    Read and set the frequency for periodic interrupts, for RTCs
    that support periodic interrupts. The periodic interrupt must
    be separately enabled or disabled using the RTC_PIE_ON,
    RTC_PIE_OFF requests. The third ioctl's argument is an
    unsigned long * or an unsigned long, respectively. The value
    is the frequency in interrupts per second. The set of allow‐
    able frequencies is the multiples of two in the range 2 to
    8192. Only a privileged process (i.e., one having the
    CAP_SYS_RESOURCE capability) can set frequencies above the
    value specified in /proc/sys/dev/rtc/max-user-freq. (This
    file contains the value 64 by default.)

RTC_EPOCH_READ, RTC_EPOCH_SET - Getting/Setting epoch

    Many RTCs encode the year in an 8-bit register which is either
    interpreted as an 8-bit binary number or as a BCD number. In
    both cases, the number is interpreted relative to this RTC's
    Epoch. The RTC's Epoch is initialized to 1900 on most systems
    but on Alpha and MIPS it might also be initialized to 1952,
    1980, or 2000, depending on the value of an RTC register for
    the year. With some RTCs, these operations can be used to
    read or to set the RTC's Epoch, respectively. The third
    ioctl's argument is an unsigned long * or an unsigned long,
    respectively, and the value returned (or assigned) is the
    Epoch. To set the RTC's Epoch the process must be privileged
    (i.e., have the CAP_SYS_TIME capability).

Implementation notes:

    All ioctls in this patch have a pointer to 'ulong' as their
    third argument. That is the reason why corresponding parts
    of added code in linux-user/syscall_defs.h contain special
    handling related to 'ulong' type: they use 'abi_ulong' type
    to make sure that ioctl's code is calculated correctly for
    both 32-bit and 64-bit targets. Also, 'MK_PTR(TYPE_ULONG)'
    is used for the similar reason in linux-user/ioctls.h.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Filip Bozuta <Filip.Bozuta@rt-rk.com>
Message-Id: <1579117007-7565-4-git-send-email-Filip.Bozuta@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>