[v9,5/8] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

Commit Message

Shiyang Ruan Sept. 15, 2021, 10:44 a.m. UTC

Punch hole on a reflinked file needs dax_iomap_cow_copy() too.
Otherwise, data in not aligned area will be not correct.  So, add the
CoW operation for not aligned case in dax_iomap_zero().

Signed-off-by: Shiyang Ruan <[e-mail]>
Reviewed-by: Ritesh Harjani <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
---
 fs/dax.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

Comments

Christoph Hellwig Sept. 16, 2021, 6:16 a.m. UTC | #1

On Wed, Sep 15, 2021 at 06:44:58PM +0800, Shiyang Ruan wrote:
> +	rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> +	if (rc < 0)
> +		goto out;
> +	memset(kaddr + offset, 0, size);
> +	if (srcmap->addr != IOMAP_HOLE && srcmap->addr != iomap->addr) {

Should we also check that ->dax_dev for iomap and srcmap are different
first to deal with case of file system with multiple devices?

Otherwise looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Shiyang Ruan Sept. 16, 2021, 8:49 a.m. UTC | #2

On 2021/9/16 14:16, Christoph Hellwig wrote:
> On Wed, Sep 15, 2021 at 06:44:58PM +0800, Shiyang Ruan wrote:
>> +	rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
>> +	if (rc < 0)
>> +		goto out;
>> +	memset(kaddr + offset, 0, size);
>> +	if (srcmap->addr != IOMAP_HOLE && srcmap->addr != iomap->addr) {
> 
> Should we also check that ->dax_dev for iomap and srcmap are different
> first to deal with case of file system with multiple devices?

I have not thought of this case.  Isn't it possible to CoW between 
different devices?


--
Thanks,
Ruan

> 
> Otherwise looks good:
> 
> Reviewed-by: Christoph Hellwig <[e-mail]>
>

Darrick J. Wong Sept. 16, 2021, 10:55 p.m. UTC | #3

On Thu, Sep 16, 2021 at 04:49:19PM +0800, Shiyang Ruan wrote:
> 
> 
> On 2021/9/16 14:16, Christoph Hellwig wrote:
> > On Wed, Sep 15, 2021 at 06:44:58PM +0800, Shiyang Ruan wrote:
> > > +	rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> > > +	if (rc < 0)
> > > +		goto out;
> > > +	memset(kaddr + offset, 0, size);
> > > +	if (srcmap->addr != IOMAP_HOLE && srcmap->addr != iomap->addr) {
> > 
> > Should we also check that ->dax_dev for iomap and srcmap are different
> > first to deal with case of file system with multiple devices?
> 
> I have not thought of this case.  Isn't it possible to CoW between different
> devices?

There's nothing in the iomap API that prevents a filesystem from doing
that, though there are no filesystems today that do such a thing.

That said, if btrfs ever joins the fold (and adds DAX support) then they
could totally COW to a different device.

--D

> 
> 
> --
> Thanks,
> Ruan
> 
> > 
> > Otherwise looks good:
> > 
> > Reviewed-by: Christoph Hellwig <[e-mail]>
> > 
> 
>

Patch

diff --git a/fs/dax.c b/fs/dax.c
index 4f346e25e488..ca4308c85988 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1212,6 +1212,7 @@  static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
 s64 dax_iomap_zero(struct iomap_iter *iter, loff_t pos, u64 length)
 {
 	const struct iomap *iomap = &iter->iomap;
+	const struct iomap *srcmap = &iter->srcmap;
 	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
 	pgoff_t pgoff;
 	long rc, id;
@@ -1230,21 +1231,27 @@  s64 dax_iomap_zero(struct iomap_iter *iter, loff_t pos, u64 length)
 
 	id = dax_read_lock();
 
-	if (page_aligned)
+	if (page_aligned) {
 		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
-	else
-		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
-	if (rc < 0) {
-		dax_read_unlock(id);
-		return rc;
+		goto out;
 	}
 
-	if (!page_aligned) {
-		memset(kaddr + offset, 0, size);
+	rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
+	if (rc < 0)
+		goto out;
+	memset(kaddr + offset, 0, size);
+	if (srcmap->addr != IOMAP_HOLE && srcmap->addr != iomap->addr) {
+		rc = dax_iomap_cow_copy(pos, size, PAGE_SIZE, srcmap,
+					kaddr);
+		if (rc < 0)
+			goto out;
+		dax_flush(iomap->dax_dev, kaddr, PAGE_SIZE);
+	} else
 		dax_flush(iomap->dax_dev, kaddr + offset, size);
-	}
+
+out:
 	dax_read_unlock(id);
-	return size;
+	return rc < 0 ? rc : size;
 }
 
 static loff_t dax_iomap_iter(const struct iomap_iter *iomi,