src/drive.c uses fread(3) like it’s read(2)

The code in src/drive.c that calls `fread(3)` treats its return (a `size_t`) as if it were the return from `read(2)` (a `ssize_t`).

For `fread(3)` the return value will never be negative. Instead, any time the return value is less than the amount requested, you need to check for both failure and EOF using `ferror(3)` and `feof(3)` respectively.
