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The drm vblank handling uses 'timeval' to store timestamps in either
monotonic or wall-clock time base. In either case, it reads the current
time as a ktime_t in get_drm_timestamp() and converts it from there.
This is a bit suspicious, as users of 'timeval' often suffer from
the time_t overflow in y2038. I have gone through this code and
found that it is unlikely to cause problems here:
- The user space ABI does not use time_t or timeval, but uses
'u32' and 'long' as the types. This means at least that rebuilding
user programs against a new libc with 64-bit time_t does not
change the ABI.
- As of commit c61eef726a ("drm: add support for monotonic vblank
timestamps") in linux-3.8, the monotonic timestamp is the default
and can only get reverted to wall-clock through a module-parameter.
- With the default monotonic timestamps, there is no problem at all.
- The drm_wait_vblank_ioctl() interface is alway safe on 64-bit
architectures, on 32-bit it might overflow the 'long' timestamps
in 2038 with wall-clock timestamps.
- The event handling uses 'u32' seconds, which overflow in 2106
on both 32-bit and 64-bit machines, when wall-clock timestamps
are used.
- The effect of overflowing either of the two is only temporary
(during the overflow, and is likely to keep working again
afterwards. It is likely the same problem as observing a
'settimeofday()' call, which was the reason for moving to the
monotonic timestamps in the first place.
Overall, this seems good enough, so my patch removes the use of
'timeval' from the vblank handling altogether and uses ktime_t
consistently, except for the part where we copy the data to user
space structures in the existing format.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.