On Tue, Mar 26, 2019 at 02:02:55PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> Add a new vm_operations struct btrfs_dax_vm_ops
> specifically for dax files.
>
> Since we will be removing(nulling) readpages/writepages for dax
> return ENOEXEC only for non-dax files.
>
> dax_insert_entry() looks ugly. Do you think we should break it
> into dax_insert_cow_entry() and dax_insert_entry()?
I would (or replace the two bools with flags), but people seem not to
like my stylistic choices. :)
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> ---
> fs/btrfs/ctree.h | 1 +
> fs/btrfs/dax.c | 11 +++++++++++
> fs/btrfs/file.c | 18 ++++++++++++++++--
> fs/dax.c | 17 ++++++++++-------
> 4 files changed, 38 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 3bcd2a4959c1..0e5060933bde 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3802,6 +3802,7 @@ int btree_readahead_hook(struct extent_buffer *eb, int err);
> /* dax.c */
> ssize_t btrfs_file_dax_read(struct kiocb *iocb, struct iov_iter *to);
> ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *from);
> +vm_fault_t btrfs_dax_fault(struct vm_fault *vmf);
> #else
> static inline ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *from)
> {
> diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
> index 49619fe3f94f..927f962d1e88 100644
> --- a/fs/btrfs/dax.c
> +++ b/fs/btrfs/dax.c
> @@ -157,4 +157,15 @@ ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *iter)
> }
> return ret;
> }
> +
> +vm_fault_t btrfs_dax_fault(struct vm_fault *vmf)
> +{
> + vm_fault_t ret;
> + pfn_t pfn;
> + ret = dax_iomap_fault(vmf, PE_SIZE_PTE, &pfn, NULL, &btrfs_iomap_ops);
> + if (ret & VM_FAULT_NEEDDSYNC)
> + ret = dax_finish_sync_fault(vmf, PE_SIZE_PTE, pfn);
> +
> + return ret;
> +}
> #endif /* CONFIG_FS_DAX */
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 3b320d0ab495..196c8f37ff9d 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -2214,15 +2214,29 @@ static const struct vm_operations_struct btrfs_file_vm_ops = {
> .page_mkwrite = btrfs_page_mkwrite,
> };
>
> +#ifdef CONFIG_FS_DAX
> +static const struct vm_operations_struct btrfs_dax_vm_ops = {
> + .fault = btrfs_dax_fault,
> + .page_mkwrite = btrfs_dax_fault,
> + .pfn_mkwrite = btrfs_dax_fault,
> +};
> +#else
> +#define btrfs_dax_vm_ops btrfs_file_vm_ops
> +#endif
> +
> static int btrfs_file_mmap(struct file *filp, struct vm_area_struct *vma)
> {
> struct address_space *mapping = filp->f_mapping;
> + struct inode *inode = file_inode(filp);
>
> - if (!mapping->a_ops->readpage)
> + if (!IS_DAX(inode) && !mapping->a_ops->readpage)
> return -ENOEXEC;
>
> file_accessed(filp);
> - vma->vm_ops = &btrfs_file_vm_ops;
> + if (IS_DAX(inode))
> + vma->vm_ops = &btrfs_dax_vm_ops;
> + else
> + vma->vm_ops = &btrfs_file_vm_ops;
>
> return 0;
> }
> diff --git a/fs/dax.c b/fs/dax.c
> index 21ee3df6f02c..41061da42771 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
Whoah, waitaminute, I thought this was a "twiddle stuff inside btrfs
only" patch...
> @@ -708,14 +708,15 @@ static int copy_user_dax(struct block_device *bdev, struct dax_device *dax_dev,
> */
> static void *dax_insert_entry(struct xa_state *xas,
> struct address_space *mapping, struct vm_fault *vmf,
> - void *entry, pfn_t pfn, unsigned long flags, bool dirty)
> + void *entry, pfn_t pfn, unsigned long flags, bool dirty,
> + bool cow)
> {
> void *new_entry = dax_make_entry(pfn, flags);
>
> if (dirty)
> __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>
> - if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {
> + if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
> unsigned long index = xas->xa_index;
> /* we are replacing a zero page with block mapping */
> if (dax_is_pmd_entry(entry))
> @@ -732,7 +733,7 @@ static void *dax_insert_entry(struct xa_state *xas,
> dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
> }
>
> - if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> + if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> /*
> * Only swap our new entry into the page cache if the current
> * entry is a zero page or an empty entry. If a normal PTE or
> @@ -1031,7 +1032,7 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
> vm_fault_t ret;
>
> *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
> - DAX_ZERO_PAGE, false);
> + DAX_ZERO_PAGE, false, false);
>
> ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);
> trace_dax_load_hole(inode, vmf, ret);
> @@ -1408,7 +1409,8 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
> goto error_finish_iomap;
>
> entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
> - 0, write && !sync);
> + 0, write && !sync,
> + (iomap.flags & IOMAP_F_COW) != 0);
Assuming you stick with bool cow, you don't need the != 0 test.
>
> /*
> * If we are doing synchronous page fault and inode needs fsync,
> @@ -1487,7 +1489,7 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
>
> pfn = page_to_pfn_t(zero_page);
> *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
> - DAX_PMD | DAX_ZERO_PAGE, false);
> + DAX_PMD | DAX_ZERO_PAGE, false, false);
>
> ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
> if (!pmd_none(*(vmf->pmd))) {
> @@ -1610,7 +1612,8 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
> goto finish_iomap;
>
> entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
> - DAX_PMD, write && !sync);
> + DAX_PMD, write && !sync,
> + false);
Why don't PMD faults support COW?
--D
>
> /*
> * If we are doing synchronous page fault and inode needs fsync,
> --
> 2.16.4
>
