[RFC PATCH 2/9] jfs: Add jfs_iomap_begin()

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Turn jfs_get_block() into a wrapper around jfs_iomap_begin().  This fixes
a latent bug where JFS was not setting b_size when it encountered a hole.
At least mpage_readahead() does not look at b_size when the buffer is
unmapped, but iomap will care whether iomap->length is set correctly,
and so we may as well set b_size correctly as well.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 fs/jfs/inode.c | 67 +++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 50 insertions(+), 17 deletions(-)

diff --git a/fs/jfs/inode.c b/fs/jfs/inode.c
index a5dd7e53754a..1a5bdaf35e9b 100644
--- a/fs/jfs/inode.c
+++ b/fs/jfs/inode.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/fs.h>
+#include <linux/iomap.h>
 #include <linux/mpage.h>
 #include <linux/buffer_head.h>
 #include <linux/pagemap.h>
@@ -196,15 +197,21 @@ void jfs_dirty_inode(struct inode *inode, int flags)
 	set_cflag(COMMIT_Dirty, inode);
 }
 
-int jfs_get_block(struct inode *ip, sector_t lblock,
-		  struct buffer_head *bh_result, int create)
+int jfs_iomap_begin(struct inode *ip, loff_t pos, loff_t length,
+		unsigned flags, struct iomap *iomap, struct iomap *srcmap)
 {
-	s64 lblock64 = lblock;
+	s64 lblock64 = pos >> ip->i_blkbits;
+	int create = flags & IOMAP_WRITE;
 	int rc = 0;
 	xad_t xad;
 	s64 xaddr;
 	int xflag;
-	s32 xlen = bh_result->b_size >> ip->i_blkbits;
+	s32 xlen;
+
+	xlen = DIV_ROUND_UP(pos + length - (lblock64 << ip->i_blkbits),
+			    i_blocksize(ip));
+	if (xlen < 0)
+		xlen = INT_MAX;
 
 	/*
 	 * Take appropriate lock on inode
@@ -214,8 +221,8 @@ int jfs_get_block(struct inode *ip, sector_t lblock,
 	else
 		IREAD_LOCK(ip, RDWRLOCK_NORMAL);
 
-	if (((lblock64 << ip->i_sb->s_blocksize_bits) < ip->i_size) &&
-	    (!xtLookup(ip, lblock64, xlen, &xflag, &xaddr, &xlen, 0)) &&
+	if (pos < ip->i_size &&
+	    !xtLookup(ip, lblock64, xlen, &xflag, &xaddr, &xlen, 0) &&
 	    xaddr) {
 		if (xflag & XAD_NOTRECORDED) {
 			if (!create)
@@ -238,13 +245,11 @@ int jfs_get_block(struct inode *ip, sector_t lblock,
 #endif				/* _JFS_4K */
 			rc = extRecord(ip, &xad);
 			if (rc)
-				goto unlock;
-			set_buffer_new(bh_result);
+				goto err;
+			iomap->flags |= IOMAP_F_NEW;
 		}
 
-		map_bh(bh_result, ip->i_sb, xaddr);
-		bh_result->b_size = xlen << ip->i_blkbits;
-		goto unlock;
+		goto map;
 	}
 	if (!create)
 		goto unlock;
@@ -254,14 +259,14 @@ int jfs_get_block(struct inode *ip, sector_t lblock,
 	 */
 #ifdef _JFS_4K
 	if ((rc = extHint(ip, lblock64 << ip->i_sb->s_blocksize_bits, &xad)))
-		goto unlock;
+		goto err;
 	rc = extAlloc(ip, xlen, lblock64, &xad, false);
 	if (rc)
-		goto unlock;
+		goto err;
 
-	set_buffer_new(bh_result);
-	map_bh(bh_result, ip->i_sb, addressXAD(&xad));
-	bh_result->b_size = lengthXAD(&xad) << ip->i_blkbits;
+	xaddr = addressXAD(&xad);
+	xlen = lengthXAD(&xad);
+	iomap->flags |= IOMAP_F_NEW;
 
 #else				/* _JFS_4K */
 	/*
@@ -271,7 +276,14 @@ int jfs_get_block(struct inode *ip, sector_t lblock,
 	BUG();
 #endif				/* _JFS_4K */
 
-      unlock:
+map:
+	iomap->addr = xaddr << ip->i_blkbits;
+	iomap->bdev = ip->i_sb->s_bdev;
+	iomap->type = IOMAP_MAPPED;
+unlock:
+	iomap->offset = lblock64 << ip->i_blkbits;
+	iomap->length = xlen << ip->i_blkbits;
+err:
 	/*
 	 * Release lock on inode
 	 */
@@ -282,6 +294,27 @@ int jfs_get_block(struct inode *ip, sector_t lblock,
 	return rc;
 }
 
+int jfs_get_block(struct inode *ip, sector_t lblock,
+		  struct buffer_head *bh_result, int create)
+{
+	struct iomap iomap = { };
+	int ret;
+
+	ret = jfs_iomap_begin(ip, lblock << ip->i_blkbits, bh_result->b_size,
+			create ? IOMAP_WRITE : 0, &iomap, NULL);
+	if (ret)
+		return ret;
+
+	bh_result->b_size = iomap.length;
+	if (iomap.type == IOMAP_HOLE)
+		return 0;
+
+	map_bh(bh_result, ip->i_sb, iomap.addr >> ip->i_blkbits);
+	if (iomap.flags & IOMAP_F_NEW)
+		set_buffer_new(bh_result);
+	return 0;
+}
+
 static int jfs_writepage(struct page *page, struct writeback_control *wbc)
 {
 	return block_write_full_page(page, jfs_get_block, wbc);
-- 
2.34.1