[PATCH v4] iomap: support tail packing inline read

[Gao Xiang]

This tries to add tail packing inline read to iomap, which can support
several inline tail blocks. Similar to the previous approach, it cleans
post-EOF in one iteration.

The write path remains untouched since EROFS cannot be used for testing.
It'd be better to be implemented if upcoming real users care rather than
leave untested dead code around.

Cc: Christoph Hellwig <hch at lst.de>
Cc: Darrick J. Wong <djwong at kernel.org>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Andreas Gruenbacher <andreas.gruenbacher at gmail.com>
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
v3: https://lore.kernel.org/r/20210719144747.189634-1-hsiangkao@linux.alibaba.com
changes since v3:
 - update return value type of iomap_read_inline_data to int;
 - fix iomap_write_begin_inline() pointed out by Andreas.

 fs/iomap/buffered-io.c | 52 ++++++++++++++++++++++++++----------------
 fs/iomap/direct-io.c   | 11 +++++----
 2 files changed, 39 insertions(+), 24 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 87ccb3438bec..0edc8bbb35d1 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -205,25 +205,25 @@ struct iomap_readpage_ctx {
 	struct readahead_control *rac;
 };
 
-static void
+static int
 iomap_read_inline_data(struct inode *inode, struct page *page,
-		struct iomap *iomap)
+		struct iomap *iomap, loff_t pos)
 {
-	size_t size = i_size_read(inode);
+	unsigned int size, poff = offset_in_page(pos);
 	void *addr;
 
-	if (PageUptodate(page))
-		return;
-
-	BUG_ON(page_has_private(page));
-	BUG_ON(page->index);
-	BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
+	/* inline source data must be inside a single page */
+	BUG_ON(iomap->length > PAGE_SIZE - offset_in_page(iomap->inline_data));
+	/* handle tail-packing blocks cross the current page into the next */
+	size = min_t(unsigned int, iomap->length + pos - iomap->offset,
+		     PAGE_SIZE - poff);
 
 	addr = kmap_atomic(page);
-	memcpy(addr, iomap->inline_data, size);
-	memset(addr + size, 0, PAGE_SIZE - size);
+	memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size);
+	memset(addr + poff + size, 0, PAGE_SIZE - poff - size);
 	kunmap_atomic(addr);
-	SetPageUptodate(page);
+	iomap_set_range_uptodate(page, poff, PAGE_SIZE - poff);
+	return PAGE_SIZE - poff;
 }
 
 static inline bool iomap_block_needs_zeroing(struct inode *inode,
@@ -246,18 +246,18 @@ 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);
-		iomap_read_inline_data(inode, page, iomap);
-		return PAGE_SIZE;
-	}
-
-	/* zero post-eof blocks as the page may be mapped */
 	iop = iomap_page_create(inode, page);
+	/* needs to skip some leading uptodate blocks */
 	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
 	if (plen == 0)
 		goto done;
 
+	if (iomap->type == IOMAP_INLINE) {
+		plen = iomap_read_inline_data(inode, page, iomap, pos);
+		goto done;
+	}
+
+	/* zero post-eof blocks as the page may be mapped */
 	if (iomap_block_needs_zeroing(inode, iomap, pos)) {
 		zero_user(page, poff, plen);
 		iomap_set_range_uptodate(page, poff, plen);
@@ -589,6 +589,18 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
 	return 0;
 }
 
+static int iomap_write_begin_inline(struct inode *inode, loff_t pos,
+		struct page *page, struct iomap *srcmap)
+{
+	/* needs more work for the tailpacking case, disable for now */
+	if (WARN_ON_ONCE(srcmap->offset != 0))
+		return -EIO;
+	if (PageUptodate(page))
+		return 0;
+	iomap_read_inline_data(inode, page, srcmap, 0);
+	return 0;
+}
+
 static int
 iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
 		struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
@@ -618,7 +630,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
 	}
 
 	if (srcmap->type == IOMAP_INLINE)
-		iomap_read_inline_data(inode, page, srcmap);
+		status = iomap_write_begin_inline(inode, pos, page, srcmap);
 	else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
 		status = __block_write_begin_int(page, pos, len, NULL, srcmap);
 	else
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 9398b8c31323..ee6309967b77 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -379,22 +379,25 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
 {
 	struct iov_iter *iter = dio->submit.iter;
 	size_t copied;
+	void *dst = iomap->inline_data + pos - iomap->offset;
 
-	BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
+	/* inline data must be inside a single page */
+	BUG_ON(length > PAGE_SIZE - offset_in_page(iomap->inline_data));
 
 	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 + size - iomap->offset,
+			       0, pos - size);
+		copied = copy_from_iter(dst, 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(dst, length, iter);
 	}
 	dio->size += copied;
 	return copied;
-- 
2.24.4