Commit a7d73fe6 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Dave Chinner
Browse files

dax: provide an iomap based fault handler 



Very similar to the existing dax_fault function, but instead of using
the get_block callback we rely on the iomap_ops vector from iomap.c.
That also avoids having to do two calls into the file system for write
faults.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
parent a254e568

fs/dax.c

+114 −0
Original line number Diff line number Diff line
@@ -1354,4 +1354,118 @@ iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter, 
	return done ? done : ret;

}

EXPORT_SYMBOL_GPL(iomap_dax_rw);



/**

 * iomap_dax_fault - handle a page fault on a DAX file

 * @vma: The virtual memory area where the fault occurred

 * @vmf: The description of the fault

 * @ops: iomap ops passed from the file system

 *

 * When a page fault occurs, filesystems may call this helper in their fault

 * or mkwrite handler for DAX files. Assumes the caller has done all the

 * necessary locking for the page fault to proceed successfully.

 */

int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,

			struct iomap_ops *ops)

{

	struct address_space *mapping = vma->vm_file->f_mapping;

	struct inode *inode = mapping->host;

	unsigned long vaddr = (unsigned long)vmf->virtual_address;

	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;

	sector_t sector;

	struct iomap iomap = { 0 };

	unsigned flags = 0;

	int error, major = 0;

	void *entry;



	/*

	 * Check whether offset isn't beyond end of file now. Caller is supposed

	 * to hold locks serializing us with truncate / punch hole so this is

	 * a reliable test.

	 */

	if (pos >= i_size_read(inode))

		return VM_FAULT_SIGBUS;



	entry = grab_mapping_entry(mapping, vmf->pgoff);

	if (IS_ERR(entry)) {

		error = PTR_ERR(entry);

		goto out;

	}



	if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)

		flags |= IOMAP_WRITE;



	/*

	 * Note that we don't bother to use iomap_apply here: DAX required

	 * the file system block size to be equal the page size, which means

	 * that we never have to deal with more than a single extent here.

	 */

	error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);

	if (error)

		goto unlock_entry;

	if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {

		error = -EIO;		/* fs corruption? */

		goto unlock_entry;

	}



	sector = iomap.blkno + (((pos & PAGE_MASK) - iomap.offset) >> 9);



	if (vmf->cow_page) {

		switch (iomap.type) {

		case IOMAP_HOLE:

		case IOMAP_UNWRITTEN:

			clear_user_highpage(vmf->cow_page, vaddr);

			break;

		case IOMAP_MAPPED:

			error = copy_user_dax(iomap.bdev, sector, PAGE_SIZE,

					vmf->cow_page, vaddr);

			break;

		default:

			WARN_ON_ONCE(1);

			error = -EIO;

			break;

		}



		if (error)

			goto unlock_entry;

		if (!radix_tree_exceptional_entry(entry)) {

			vmf->page = entry;

			return VM_FAULT_LOCKED;

		}

		vmf->entry = entry;

		return VM_FAULT_DAX_LOCKED;

	}



	switch (iomap.type) {

	case IOMAP_MAPPED:

		if (iomap.flags & IOMAP_F_NEW) {

			count_vm_event(PGMAJFAULT);

			mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);

			major = VM_FAULT_MAJOR;

		}

		error = dax_insert_mapping(mapping, iomap.bdev, sector,

				PAGE_SIZE, &entry, vma, vmf);

		break;

	case IOMAP_UNWRITTEN:

	case IOMAP_HOLE:

		if (!(vmf->flags & FAULT_FLAG_WRITE))

			return dax_load_hole(mapping, entry, vmf);

		/*FALLTHRU*/

	default:

		WARN_ON_ONCE(1);

		error = -EIO;

		break;

	}



 unlock_entry:

	put_locked_mapping_entry(mapping, vmf->pgoff, entry);

 out:

	if (error == -ENOMEM)

		return VM_FAULT_OOM | major;

	/* -EBUSY is fine, somebody else faulted on the same PTE */

	if (error < 0 && error != -EBUSY)

		return VM_FAULT_SIGBUS | major;

	return VM_FAULT_NOPAGE | major;

}

EXPORT_SYMBOL_GPL(iomap_dax_fault);

#endif /* CONFIG_FS_IOMAP */

include/linux/dax.h

+2 −0
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *, 
		  get_block_t, dio_iodone_t, int flags);

int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);

int dax_truncate_page(struct inode *, loff_t from, get_block_t);

int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,

			struct iomap_ops *ops);

int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);

int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);

void dax_wake_mapping_entry_waiter(struct address_space *mapping,