Re: [Qemu-devel] [PATCH v4 5/5] xfs: disable map_sync for async flush

[Darrick J. Wong]

On Thu, Apr 04, 2019 at 09:09:12AM +1100, Dave Chinner wrote:
> On Wed, Apr 03, 2019 at 04:10:18PM +0530, Pankaj Gupta wrote:
> > Virtio pmem provides asynchronous host page cache flush
> > mechanism. we don't support 'MAP_SYNC' with virtio pmem 
> > and xfs.
> > 
> > Signed-off-by: Pankaj Gupta <address@hidden>
> > ---
> >  fs/xfs/xfs_file.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 1f2e2845eb76..dced2eb8c91a 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -1203,6 +1203,14 @@ xfs_file_mmap(
> >     if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC))
> >             return -EOPNOTSUPP;
> >  
> > +   /* We don't support synchronous mappings with DAX files if
> > +    * dax_device is not synchronous.
> > +    */
> > +   if (IS_DAX(file_inode(filp)) && !dax_synchronous(
> > +           xfs_find_daxdev_for_inode(file_inode(filp))) &&
> > +                                   (vma->vm_flags & VM_SYNC))
> > +           return -EOPNOTSUPP;
> > +
> >     file_accessed(filp);
> >     vma->vm_ops = &xfs_file_vm_ops;
> >     if (IS_DAX(file_inode(filp)))
> 
> All this ad hoc IS_DAX conditional logic is getting pretty nasty.
> 
> xfs_file_mmap(
> ....
> {
>       struct inode    *inode = file_inode(filp);
> 
>       if (vma->vm_flags & VM_SYNC) {
>               if (!IS_DAX(inode))
>                       return -EOPNOTSUPP;
>               if (!dax_synchronous(xfs_find_daxdev_for_inode(inode))
>                       return -EOPNOTSUPP;
>       }
> 
>       file_accessed(filp);
>       vma->vm_ops = &xfs_file_vm_ops;
>       if (IS_DAX(inode))
>               vma->vm_flags |= VM_HUGEPAGE;
>       return 0;
> }
> 
> 
> Even better, factor out all the "MAP_SYNC supported" checks into a
> helper so that the filesystem code just doesn't have to care about
> the details of checking for DAX+MAP_SYNC support....

Seconded, since ext4 has nearly the same flag validation logic.

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> address@hidden