On Thu, Oct 15, 2020 at 10:49:01AM +0100, Christoph Hellwig wrote:

quoted

+iomap_zero_range_skip_uncached(struct inode *inode, loff_t *pos,
+		loff_t *count, loff_t *written)
+{
+	unsigned dirty_offset, bytes = 0;
+
+	dirty_offset = page_cache_seek_hole_data(inode, *pos, *count,
+				SEEK_DATA);
+	if (dirty_offset == -ENOENT)
+		bytes = *count;
+	else if (dirty_offset > *pos)
+		bytes = dirty_offset - *pos;
+
+	if (bytes) {
+		*pos += bytes;
+		*count -= bytes;
+		*written += bytes;
+	}

I find the calling conventions weird.  why not return bytes and
keep the increments/decrements of the three variables in the caller?

No particular reason. IIRC I had it both ways and just landed on this.
I'd change it, but as mentioned in the patch 1 thread I don't think this
patch is sufficient (with or without patch 1) anyways because the page
can also have been reclaimed before we get here.

Brian