[PATCH 08/15] dax: add dax_iomap_cow to copy a mmap page before writing

[Goldwyn Rodrigues]

From: Goldwyn Rodrigues <rgold...@suse.com>

dax_iomap_cow copies a page before presenting for mmap.

Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com>
---
 fs/dax.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index e254535dd830..21ee3df6f02c 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1269,6 +1269,33 @@ static bool dax_fault_is_synchronous(unsigned long flags,
                && (iomap->flags & IOMAP_F_DIRTY);
 }
 
+static int dax_iomap_cow(struct iomap *iomap, loff_t pos, pfn_t *pfn)
+{
+       void *daddr;
+       pgoff_t pgoff;
+       long rc;
+       int id;
+       sector_t sector;
+
+       pos = round_down(pos, PAGE_SIZE);
+
+       sector = round_down(iomap->addr + iomap->offset - pos, PAGE_SIZE) >> 9;
+       rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);
+       if (rc)
+               return rc;
+
+       id = dax_read_lock();
+       rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &daddr, pfn);
+       if (rc < 0)
+               goto out;
+
+       dax_to_dax_copy(iomap, pos, daddr, PAGE_SIZE);
+
+out:
+       dax_read_unlock(id);
+       return rc;
+}
+
 static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
                               int *iomap_errp, const struct iomap_ops *ops)
 {
@@ -1372,7 +1399,11 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault 
*vmf, pfn_t *pfnp,
                        count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
                        major = VM_FAULT_MAJOR;
                }
-               error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
+
+               if (iomap.flags & IOMAP_F_COW)
+                       error = dax_iomap_cow(&iomap, pos, &pfn);
+               else
+                       error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
                if (error < 0)
                        goto error_finish_iomap;
 
-- 
2.16.4