On Fri, Dec 17, 2021 at 10:48:23AM +1100, NeilBrown wrote: > Currently various places test if direct IO is possible on a file by > checking for the existence of the direct_IO address space operation. > This is a poor choice, as the direct_IO operation may not be used - it is > only used if the generic_file_*_iter functions are called for direct IO > and some filesystems - particularly NFS - don't do this. > > Instead, introduce a new mapping flag: AS_CAN_DIO and change the various > places to check this (avoiding a pointer dereference). > unlock_new_inode() will set this flag if ->direct_IO is present, so > filesystems do not need to be changed. > > NFS *is* changed, to set the flag explicitly and discard the direct_IO > entry in the address_space_operations for files. For other can flags related to file operations we usuall stash them into file->f_mode. Any reason to treat this different?
