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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
diff --git a/fs/dax.c b/fs/dax.c
index 1f9f2d4..cc025f8 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1354,4 +1354,118 @@
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 */