When compiling this for older kernels using the compatibility build the compiler complains about uninitialized variables: In file included from include/linux/kernel.h:20:0, from include/linux/cache.h:4, from include/linux/time.h:7, from include/linux/input.h:13, from /home/hans/work/build/media_build/v4l/compat.h:9, from <command-line>:0: /home/hans/work/build/media_build/v4l/videobuf2-core.c: In function 'vb2_mmap': include/linux/dynamic_debug.h:60:9: warning: 'plane' may be used uninitialized in this function [-Wmaybe-uninitialized] printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); \ ^ /home/hans/work/build/media_build/v4l/videobuf2-core.c:2381:23: note: 'plane' was declared here unsigned int buffer, plane; ^ In file included from include/linux/kernel.h:20:0, from include/linux/cache.h:4, from include/linux/time.h:7, from include/linux/input.h:13, from /home/hans/work/build/media_build/v4l/compat.h:9, from <command-line>:0: include/linux/dynamic_debug.h:60:9: warning: 'buffer' may be used uninitialized in this function [-Wmaybe-uninitialized] printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); \ ^ /home/hans/work/build/media_build/v4l/videobuf2-core.c:2381:15: note: 'buffer' was declared here unsigned int buffer, plane; ^ While these warnings are bogus (the call to __find_plane_by_offset will set buffer and plane), it doesn't hurt to initialize these variables. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>