iomap: Support inline data with block size < page size

Remove the restriction that inline data must start on a page boundary
in a file.  This allows, for example, the first 2KiB to be stored out
of line and the trailing 30 bytes to be stored inline.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/iomap/buffered-io.c

@@ -209,28 +209,26 @@ static int iomap_read_inline_data(struct inode *inode, struct page *page,
 		struct iomap *iomap)
 {
 	size_t size = i_size_read(inode) - iomap->offset;
+	size_t poff = offset_in_page(iomap->offset);
 	void *addr;
 
 	if (PageUptodate(page))
-		return 0;
+		return PAGE_SIZE - poff;
 
-	/* inline data must start page aligned in the file */
-	if (WARN_ON_ONCE(offset_in_page(iomap->offset)))
-		return -EIO;
 	if (WARN_ON_ONCE(size > PAGE_SIZE -
 			 offset_in_page(iomap->inline_data)))
 		return -EIO;
 	if (WARN_ON_ONCE(size > iomap->length))
 		return -EIO;
-	if (WARN_ON_ONCE(page_has_private(page)))
-		return -EIO;
+	if (poff > 0)
+		iomap_page_create(inode, page);
 
-	addr = kmap_atomic(page);
+	addr = kmap_atomic(page) + poff;
 	memcpy(addr, iomap->inline_data, size);
-	memset(addr + size, 0, PAGE_SIZE - size);
+	memset(addr + size, 0, PAGE_SIZE - poff - size);
 	kunmap_atomic(addr);
-	SetPageUptodate(page);
-	return 0;
+	iomap_set_range_uptodate(page, poff, PAGE_SIZE - poff);
+	return PAGE_SIZE - poff;
 }
 
 static inline bool iomap_block_needs_zeroing(struct inode *inode,
@@ -252,13 +250,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	unsigned poff, plen;
 	sector_t sector;
 
-	if (iomap->type == IOMAP_INLINE) {
-		int ret = iomap_read_inline_data(inode, page, iomap);
-
-		if (ret)
-			return ret;
-		return PAGE_SIZE;
-	}
+	if (iomap->type == IOMAP_INLINE)
+		return iomap_read_inline_data(inode, page, iomap);
 
 	/* zero post-eof blocks as the page may be mapped */
 	iop = iomap_page_create(inode, page);
@@ -593,10 +586,15 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
 static int iomap_write_begin_inline(struct inode *inode,
 		struct page *page, struct iomap *srcmap)
 {
+	int ret;
+
 	/* needs more work for the tailpacking case; disable for now */
 	if (WARN_ON_ONCE(srcmap->offset != 0))
 		return -EIO;
-	return iomap_read_inline_data(inode, page, srcmap);
+	ret = iomap_read_inline_data(inode, page, srcmap);
+	if (ret < 0)
+		return ret;
+	return 0;
 }
 
 static int