Re: [RFC PATCH] iomap: generalize IOMAP_INLINE to cover tail-packing case

[Andreas Gruenbacher <agruenba@redhat.com>]

Something along the lines of the attached, broken patch might work in
the end.

Andreas

---
 fs/buffer.c           | 10 ++++--
 fs/iomap.c            | 74 +++++++++++++++++++++++++++++--------------
 include/linux/iomap.h |  3 ++
 3 files changed, 61 insertions(+), 26 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index e450c55f6434..8d8668e377ab 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1873,8 +1873,8 @@ void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
 EXPORT_SYMBOL(page_zero_new_buffers);
 
 static void
-iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
-		struct iomap *iomap)
+iomap_to_bh(struct inode *inode, struct page *page, sector_t block,
+		struct buffer_head *bh, struct iomap *iomap)
 {
 	loff_t offset = block << inode->i_blkbits;
 
@@ -1924,6 +1924,10 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 				inode->i_blkbits;
 		set_buffer_mapped(bh);
 		break;
+	case IOMAP_INLINE:
+		__iomap_read_inline_data(inode, page, iomap);
+		set_buffer_uptodate(bh);
+		break;
 	}
 }
 
@@ -1969,7 +1973,7 @@ int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
 				if (err)
 					break;
 			} else {
-				iomap_to_bh(inode, block, bh, iomap);
+				iomap_to_bh(inode, page, block, bh, iomap);
 			}
 
 			if (buffer_new(bh)) {
diff --git a/fs/iomap.c b/fs/iomap.c
index 45aa58e837b5..61188e95def2 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -260,24 +260,47 @@ struct iomap_readpage_ctx {
 	struct list_head	*pages;
 };
 
-static void
-iomap_read_inline_data(struct inode *inode, struct page *page,
+#define offset_in_block(offset, inode) \
+	((unsigned long)(offset) & (i_blocksize(inode) - 1))
+
+static bool
+inline_data_within_block(struct inode *inode, struct iomap *iomap,
+		unsigned int size)
+{
+	unsigned int off = offset_in_block(iomap->inline_data, inode);
+
+	return size <= i_blocksize(inode) - off;
+}
+
+void
+__iomap_read_inline_data(struct inode *inode, struct page *page,
 		struct iomap *iomap)
 {
-	size_t size = i_size_read(inode);
+	size_t size = offset_in_block(i_size_read(inode), inode);
+	unsigned int poff = offset_in_page(iomap->offset);
+	unsigned int bsize = i_blocksize(inode);
 	void *addr;
 
 	if (PageUptodate(page))
 		return;
 
-	BUG_ON(page->index);
-	BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
+	BUG_ON(!inline_data_within_block(inode, iomap, size));
 
 	addr = kmap_atomic(page);
-	memcpy(addr, iomap->inline_data, size);
-	memset(addr + size, 0, PAGE_SIZE - size);
+	memcpy(addr + poff, iomap->inline_data, size);
+	memset(addr + poff + size, 0, bsize - size);
 	kunmap_atomic(addr);
-	SetPageUptodate(page);
+}
+
+static void
+iomap_read_inline_data(struct inode *inode, struct page *page,
+		struct iomap *iomap)
+{
+	unsigned int poff = offset_in_page(iomap->offset);
+	unsigned int bsize = i_blocksize(inode);
+
+	__iomap_read_inline_data(inode, page, iomap);
+	iomap_set_range_uptodate(page, poff, bsize);
 }
 
 static loff_t
@@ -292,11 +315,8 @@ 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) {
-		WARN_ON_ONCE(pos);
+	if (iomap->type == IOMAP_INLINE)
 		iomap_read_inline_data(inode, page, iomap);
-		return PAGE_SIZE;
-	}
 
 	/* zero post-eof blocks as the page may be mapped */
 	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
@@ -637,6 +657,11 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len,
 	if (PageUptodate(page))
 		return 0;
 
+	if (iomap->type == IOMAP_INLINE) {
+		iomap_read_inline_data(inode, page, iomap);
+		return 0;
+	}
+
 	do {
 		iomap_adjust_read_range(inode, iop, &block_start,
 				block_end - block_start, &poff, &plen);
@@ -682,9 +707,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
 		goto out_no_page;
 	}
 
-	if (iomap->type == IOMAP_INLINE)
-		iomap_read_inline_data(inode, page, iomap);
-	else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
+	if (iomap->flags & IOMAP_F_BUFFER_HEAD)
 		status = __block_write_begin_int(page, pos, len, NULL, iomap);
 	else
 		status = __iomap_write_begin(inode, pos, len, page, iomap);
@@ -761,11 +784,11 @@ iomap_write_end_inline(struct inode *inode, struct page *page,
 {
 	void *addr;
 
-	WARN_ON_ONCE(!PageUptodate(page));
-	BUG_ON(pos + copied > PAGE_SIZE - offset_in_page(iomap->inline_data));
+	BUG_ON(!inline_data_within_block(inode, iomap, pos + copied));
 
 	addr = kmap_atomic(page);
-	memcpy(iomap->inline_data + pos, addr + pos, copied);
+	memcpy(iomap->inline_data + offset_in_block(pos, inode),
+	       addr + offset_in_page(pos), copied);
 	kunmap_atomic(addr);
 
 	mark_inode_dirty(inode);
@@ -1064,7 +1087,7 @@ iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
 		const struct iomap_ops *ops)
 {
 	unsigned int blocksize = i_blocksize(inode);
-	unsigned int off = pos & (blocksize - 1);
+	unsigned int off = offset_in_block(pos, inode);
 
 	/* Block boundary? Nothing to do */
 	if (!off)
@@ -1772,21 +1795,26 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
 	struct iov_iter *iter = dio->submit.iter;
 	size_t copied;
 
-	BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
+	BUG_ON(!inline_data_within_block(inode, iomap, pos + length));
 
 	if (dio->flags & IOMAP_DIO_WRITE) {
 		loff_t size = inode->i_size;
 
 		if (pos > size)
-			memset(iomap->inline_data + size, 0, pos - size);
-		copied = copy_from_iter(iomap->inline_data + pos, length, iter);
+			memset(iomap->inline_data +
+			       offset_in_block(size, inode), 0, pos - size);
+		copied = copy_from_iter(iomap->inline_data +
+					offset_in_block(pos, inode),
+					length, iter);
 		if (copied) {
 			if (pos + copied > size)
 				i_size_write(inode, pos + copied);
 			mark_inode_dirty(inode);
 		}
 	} else {
-		copied = copy_to_iter(iomap->inline_data + pos, length, iter);
+		copied = copy_to_iter(iomap->inline_data +
+				      offset_in_block(pos, inode),
+				      length, iter);
 	}
 	dio->size += copied;
 	return copied;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 2103b94cb1bf..a8a60dd2fdc0 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -131,6 +131,9 @@ static inline struct iomap_page *to_iomap_page(struct page *page)
 	return NULL;
 }
 
+void __iomap_read_inline_data(struct inode *inode, struct page *page,
+		struct iomap *iomap);
+
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops);
 int iomap_readpage(struct page *page, const struct iomap_ops *ops);
-- 
2.20.1