[commandersaki]

you lose explicit error handling

I've never had to use mmap but this is always been the issue in my head. If you're treating I/O as memory pages, what happens when you read a page and it needs to "fault" by reading the backing storage but the storage fails to deliver? What can be said at that point, or does the program crash?

[kennethallen]

If you fail to load an mmapped page because of an I/O error, Unix-like OSes interrupt your program with SIGBUS/SIGSEGV. It might be technically possible to write a program that would handle those signals and recover, but it seems like a lot more work and complexity than just checking errno after a read system call.