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04_AdvancedFileIO/README.md

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+# Chapter 4 – Advanced File I/O
+
+## Scatter/Gather I/O
+- Scatter/gather I/O allows reading or writing data to/from multiple buffers in a single system call.
+- Uses `readv()` and `writev()`:
+  - `readv(fd, iov, iovcnt)`: reads into multiple buffers (`iov` array).
+  - `writev(fd, iov, iovcnt)`: writes from multiple buffers.
+- Improves efficiency by reducing system calls.
+
+## Event Poll (`select()`, `poll()`, `epoll`)
+- Traditional multiplexing: `select()`, `poll()` (limited scalability).
+- Linux-specific: `epoll` for efficient event notification.
+  - `epoll_create()`: create epoll instance.
+  - `epoll_ctl()`: control interest list (add, modify, remove fds).
+  - `epoll_wait()`: wait for events.
+- Edge-triggered vs level-triggered modes.
+
+## Memory-Mapped Files (`mmap()`)
+- Maps files or devices into memory for direct access.
+- System calls: `mmap()`, `munmap()`.
+- Benefits: faster I/O, shared memory.
+- Use `msync()` to synchronize changes.
+- Resizing mappings, changing protections.
+- Advisory calls:
+  - `posix_fadvise()`: give advice about expected I/O patterns.
+  - `readahead()`: prefetch file data.
+- Pros and cons of memory mapping.
+
+## Asynchronous I/O and I/O Scheduling
+- Distinction between synchronous and asynchronous I/O.
+- Linux AIO APIs for asynchronous operations.
+- I/O schedulers:
+  - Manage disk request ordering.
+  - Examples: CFQ, noop, deadline.
+- Optimizing I/O performance by choosing schedulers.
+- Concepts of disk addressing and request life cycle.
+
+## Miscellaneous
+- `ioctl()`: device-specific operations.
+- Zero-copy transfers: `sendfile()`, `splice()`.
+
+---
+
+> This chapter covers advanced Linux I/O techniques aimed at improving performance and flexibility in system programming.
+