On Tue, 21 Dec 2021, Christoph Hellwig wrote: > 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? f_mode is a much better place to put the flag! Thanks for that suggestion and all the other feedback. I'll post a new series early next week. Thanks, NeilBrown
