To generate this patch, we can follow these reasoning steps:

Step 1. Root Cause Analysis:

1. Identify the vulnerable operation:
   - The vulnerability occurs in the expression: `map.m_len << inode->i_blkbits`
   - This is a left shift operation, which can lead to integer overflow if not handled carefully.

2. Analyze the data types:
   - `map.m_len` is likely an integer type (int or unsigned int)
   - `inode->i_blkbits` is also likely an integer type
   - The result is assigned to `bh->b_size`, which might be a larger integer type

3. Understand the potential overflow:
   - If `map.m_len` is large and `inode->i_blkbits` is not small, the left shift operation can cause an integer overflow
   - This overflow can lead to unexpected results or security vulnerabilities

4. Consider the context:
   - This operation is calculating a size, which suggests it should always be positive and potentially large

Step 2. Fixing Strategy:

1. Prevent integer overflow:
   - To avoid overflow, we need to ensure the operation is performed using a larger data type

2. Choose an appropriate data type:
   - `u64` (unsigned 64-bit integer) is a good choice for size calculations as it can represent very large values

3. Apply the fix:
   - Cast `map.m_len` to `u64` before the left shift operation
   - This ensures the entire calculation is performed using 64-bit arithmetic, preventing overflow

4. Resulting patch:
   ```
   < 		bh->b_size = map.m_len << inode->i_blkbits;
   ---
   > 		bh->b_size = (u64)map.m_len << inode->i_blkbits;
   ```

This patch addresses the CWE-190 (Integer Overflow or Wraparound) vulnerability by ensuring that the calculation is performed using a 64-bit unsigned integer, which can safely handle much larger values without overflow.