It seems all filesystems but XFS ignore O_SYNC for fallocate, and never make sure the size update transaction made it to disk. Given that a fallocate without FALLOC_FL_KEEP_SIZE very much is a data operation (it adds new blocks that return zeroes) that seems like a fairly nasty surprise for O_SYNC users. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html