Increasing a file's size using mmap
linux, memory-mapped-files, mmap, python
Solution
On POSIX systems at least, `mmap()` cannot be used to increase (or decrease) the size of a file. `mmap()`'s function is to memory map a portion of a file. It's logical that the thing you request to map should actually exist! Frankly, I'm really surprised that you would actually be able to do this under MS Windows.
If you want to grow a file, just `ftruncate()` it before you `mmap()` it.
Problem
In Python on Windows I can create a large file by ``` from mmap import mmap f = open('big.file', 'w') f.close() f = open('big.file', 'r+') m = mmap(f.fileno(), 10**9) ``` And now `big.file` is (about) 1 gigabyte. On Linux, though, this will return `ValueError: mmap length is greater than file size`. Is there a way to get the same behavior on Linux as with Windows? That is, to be able to increase a file's size using `mmap`?