On Mon, Jan 24, 2022 at 02:48:32PM +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 f_mode flag: FMODE_CAN_ODIRECT and change the > various places to check this (avoiding pointer dereferences). > do_dentry_open() 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. Looks good: Reviewed-by: Christoph Hellwig <hch@xxxxxx> It would be nice to throw in a cleanup to remove noop_direct_IO as well.