Today's linux-next build (powerpc ppc44x_defconfig) failed like this:
drivers/mtd/ubi/gluebi.c: In function 'gluebi_get_device':
drivers/mtd/ubi/gluebi.c:126: error: implicit declaration of function 'IS_ERR'
drivers/mtd/ubi/gluebi.c:129: error: implicit declaration of function 'PTR_ERR'
Introduced by commit ec5c514efde253de7f28668c88bbae26d2a293de ("UBI: make
gluebi a separate module") from the ubi tree. I guess the conversion
managed to remove an implicit include of linux/err.h.
I have reverted that commit for today. I then needed to also revert
commit 518ceef0c9ca97023e45ae46aedaefa240c690a6 ("UBI: remove built-in
gluebi") to make it build again.