On 2021/2/8 下午11:19, Christoph Hellwig wrote:
On Mon, Feb 08, 2021 at 01:09:22AM +0800, Shiyang Ruan wrote:
With dax we cannot deal with readpage() etc. So, we create a
funciton callback to perform the file data comparison and pass

s/funciton/function/g

+#define MIN(a, b) (((a) < (b)) ? (a) : (b))

This should use the existing min or min_t helpers.


  int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
                                  struct file *file_out, loff_t pos_out,
-                                 loff_t *len, unsigned int remap_flags)
+                                 loff_t *len, unsigned int remap_flags,
+                                 compare_range_t compare_range_fn)

Can we keep generic_remap_file_range_prep as-is, and add a new
dax_remap_file_range_prep, both sharing a low-level
__generic_remap_file_range_prep implementation?  And for that
implementation I'd also go for classic if/else instead of the function
pointer.

The dax dedupe comparison need the iomap_ops pointer as argument, so my understanding is that we don't modify the argument list of generic_remap_file_range_prep(), but move its code into __generic_remap_file_range_prep() whose argument list can be modified to accepts the iomap_ops pointer. Then it looks like this:

```
int dax_remap_file_range_prep(struct file *file_in, loff_t pos_in,
                                  struct file *file_out, loff_t pos_out,
                                  loff_t *len, unsigned int remap_flags,
                                  const struct iomap_ops *ops)
{
        return __generic_remap_file_range_prep(file_in, pos_in, file_out,
                        pos_out, len, remap_flags, ops);
}
EXPORT_SYMBOL(dax_remap_file_range_prep);

int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
                                  struct file *file_out, loff_t pos_out,
                                  loff_t *len, unsigned int remap_flags)
{
        return __generic_remap_file_range_prep(file_in, pos_in, file_out,
                        pos_out, len, remap_flags, NULL);
}
EXPORT_SYMBOL(generic_remap_file_range_prep);
```

Am i right?


--
Thanks,
Ruan Shiyang.


+extern int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
+                                        struct inode *dest, loff_t destoff,
+                                        loff_t len, bool *is_same);

no need for the extern.




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