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    SubjectRe: [PATCH 08/18] MM: Add AS_CAN_DIO mapping flag
    On Thu, 16 Dec 2021 at 23:57, NeilBrown <neilb@suse.de> 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.
    ...
    > diff --git a/fs/inode.c b/fs/inode.c
    > index 6b80a51129d5..bae65ccecdb1 100644
    > --- a/fs/inode.c
    > +++ b/fs/inode.c
    > @@ -1008,6 +1008,9 @@ EXPORT_SYMBOL(lockdep_annotate_inode_mutex_key);
    > void unlock_new_inode(struct inode *inode)
    > {
    > lockdep_annotate_inode_mutex_key(inode);
    > + if (inode->i_mapping->a_ops &&
    > + inode->i_mapping->a_ops->direct_IO)
    > + set_bit(AS_CAN_DIO, &inode->i_mapping->flags);
    > spin_lock(&inode->i_lock);
    > WARN_ON(!(inode->i_state & I_NEW));
    > inode->i_state &= ~I_NEW & ~I_CREATING;

    Does d_instantiate_new() also need to set AS_CAN_DIO?

    Mark

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