On Thu 21-12-17 09:12:52, Dan Williams wrote:
> On Thu, Dec 21, 2017 at 8:30 AM, Jan Kara <jack@xxxxxxx> wrote:
> > Ext4 needs to pass through error from its iomap handler to the page
> > fault handler so that it can properly detect ENOSPC and force
> > transaction commit and retry the fault (and block allocation). Add
> > argument to dax_iomap_fault() for passing such error.
> >
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> > fs/dax.c | 9 ++++++---
> > fs/ext2/file.c | 2 +-
> > fs/ext4/file.c | 2 +-
> > fs/xfs/xfs_file.c | 2 +-
> > include/linux/dax.h | 2 +-
> > 5 files changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index 95981591977a..f3afa1d6156c 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1096,7 +1096,7 @@ static bool dax_fault_is_synchronous(unsigned long flags,
> > }
> >
> > static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
> > - const struct iomap_ops *ops)
> > + int *iomap_errp, const struct iomap_ops *ops)
> > {
> > struct vm_area_struct *vma = vmf->vma;
> > struct address_space *mapping = vma->vm_file->f_mapping;
> > @@ -1149,6 +1149,8 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
> > * that we never have to deal with more than a single extent here.
> > */
> > error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
> > + if (iomap_errp)
> > + *iomap_errp = error;
>
> Since we already have 'struct iomap' tracking the state of the iomap
> should we track the error status there as well? I.e. move the on
> stack allocation of struct iomap to the per-fs dax fault handlers.
I don't think that's really adequate. Firstly because at least part of
struct iomap needs to be initialized inside dax_iomap_fault() and secondly
because by the time dax_iomap_fault() returns, mapping information in struct
iomap may be invalid (as we unlocked radix tree entry). So I think it is
really better to pass back only the error code and keep struct iomap
internal to dax_iomap_fault().
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
