ext4: create EXT4_MAX_BLOCKS() macro

Create a macro to calculate length + offset -> maximum blocks
This adds more readability.
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -262,6 +262,9 @@ struct ext4_io_submit {
 				 (s)->s_first_ino)
 #endif
 #define EXT4_BLOCK_ALIGN(size, blkbits)		ALIGN((size), (1 << (blkbits)))
+#define EXT4_MAX_BLOCKS(size, offset, blkbits) \
+	((EXT4_BLOCK_ALIGN(size + offset, blkbits) >> blkbits) - (offset >> \
+								  blkbits))
 
 /* Translate a block number to a cluster number */
 #define EXT4_B2C(sbi, blk)	((blk) >> (sbi)->s_cluster_bits)

fs/ext4/extents.c

@@ -4961,13 +4961,8 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 
 	trace_ext4_fallocate_enter(inode, offset, len, mode);
 	lblk = offset >> blkbits;
-	/*
-	 * We can't just convert len to max_blocks because
-	 * If blocksize = 4096 offset = 3072 and len = 2048
-	 */
-	max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
-		- lblk;
 
+	max_blocks = EXT4_MAX_BLOCKS(len, offset, blkbits);
 	flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
 	if (mode & FALLOC_FL_KEEP_SIZE)
 		flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
@@ -5030,12 +5025,8 @@ int ext4_convert_unwritten_extents(handle_t *handle, struct inode *inode,
 	unsigned int credits, blkbits = inode->i_blkbits;
 
 	map.m_lblk = offset >> blkbits;
-	/*
-	 * We can't just convert len to max_blocks because
-	 * If blocksize = 4096 offset = 3072 and len = 2048
-	 */
-	max_blocks = ((EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits) -
-		      map.m_lblk);
+	max_blocks = EXT4_MAX_BLOCKS(len, offset, blkbits);
+
 	/*
 	 * This is somewhat ugly but the idea is clear: When transaction is
 	 * reserved, everything goes into it. Otherwise we rather start several

fs/ext4/file.c

@@ -144,8 +144,7 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			int err, len;
 
 			map.m_lblk = pos >> blkbits;
-			map.m_len = (EXT4_BLOCK_ALIGN(pos + length, blkbits) >> blkbits)
-				- map.m_lblk;
+			map.m_len = EXT4_MAX_BLOCKS(length, pos, blkbits);
 			len = map.m_len;
 
 			err = ext4_map_blocks(NULL, inode, &map, 0);