Chapter 4

chp4/README.md

@@ -1,42 +1,45 @@
 # Chapter 4 – Advanced File I/O
 
-## File Metadata and the `stat` Family
+## Scatter/Gather I/O
-- Use `stat()`, `fstat()`, `lstat()` to retrieve file metadata:
+- Scatter/gather I/O allows reading or writing data to/from multiple buffers in a single system call.
-  - File type, size, inode number, permissions, ownership, timestamps (atime, mtime, ctime).
+- Uses `readv()` and `writev()`:
-- The `stat` structure includes all these details.
+  - `readv(fd, iov, iovcnt)`: reads into multiple buffers (`iov` array).
+  - `writev(fd, iov, iovcnt)`: writes from multiple buffers.
+- Improves efficiency by reducing system calls.
 
-## File Types
+## Event Poll (`select()`, `poll()`, `epoll`)
-- Regular file, directory, symbolic link, character/block device, FIFO, socket.
+- Traditional multiplexing: `select()`, `poll()` (limited scalability).
-- Use macros like `S_ISREG()`, `S_ISDIR()` to test file types.
+- 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.
 
-## File Permissions and Modes
+## Memory-Mapped Files (`mmap()`)
-- Represented by 12 bits (e.g., `rwxr-xr--`), plus sticky/SUID/SGID bits.
+- Maps files or devices into memory for direct access.
-- Manipulate with `chmod()`, `fchmod()`, `umask()`.
+- System calls: `mmap()`, `munmap()`.
-- Ownership changed with `chown()` and `fchown()`.
+- 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.
 
-## Links
+## Asynchronous I/O and I/O Scheduling
-- **Hard links**: multiple filenames point to the same inode.
+- Distinction between synchronous and asynchronous I/O.
-- **Symbolic links**: separate files that reference other paths; can be broken.
+- Linux AIO APIs for asynchronous operations.
-- Use `link()`, `unlink()`, `symlink()`, `readlink()`.
+- 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.
 
-## Directories
+## Miscellaneous
-- Open with `opendir()`, read entries with `readdir()`.
+- `ioctl()`: device-specific operations.
-- Low-level: `getdents()` system call.
+- Zero-copy transfers: `sendfile()`, `splice()`.
 
-## File Timestamps
+---
-- `utime()`, `utimes()`, `futimens()`, and `utimensat()` to update access/modification times.
 
-## File Descriptors and Flags
+> This chapter covers advanced Linux I/O techniques aimed at improving performance and flexibility in system programming.
-- Manipulate with `fcntl()`:
-  - Set non-blocking mode (`O_NONBLOCK`), FD_CLOEXEC flag, file locks.
-  - Duplicate with `dup()` and `dup2()`.
 
-## File Locking
-- `flock()` for advisory locking (whole file).
-- `fcntl()` for POSIX record locking (ranges).
-
-## Temporary Files
-- `tmpfile()`, `mkstemp()` are safe methods to create temp files.
-
-## Summary
-- Chapter 3 focuses on extended file handling: metadata, links, directories, file modes, and advanced descriptor manipulation.

chp4/readv.c

@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+int main(void) {
+    char foo[48], bar[51], baz[49];
+    int fd = open("buccaneer.txt", O_RDONLY);
+    if (fd == -1) {
+        perror("open");
+        return 1;
+    }
+
+    // setup our iovec structures
+    struct iovec iov[3];
+    iov[0].iov_base = foo;
+    iov[0].iov_len = sizeof(foo);
+    iov[1].iov_base = bar;
+    iov[1].iov_len = sizeof(bar);
+    iov[2].iov_base = baz;
+    iov[2].iov_len = sizeof(baz);
+
+    // read into the structures with a single call
+    int nr = readv(fd, iov, 3);
+    if (nr == -1) {
+        perror("readv");
+        return 1;
+    }
+
+    for (int i = 0; i < 3; i++)
+        printf("%d: %s", i, (char *)iov[i].iov_base);
+
+    if (close(fd)) {
+        perror("close");
+        return 1;
+    }
+
+    return 0;
+}

chp4/writev.c

@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+int main(void) {
+    struct iovec iov[3];
+
+    char *buf[] = {
+        "The term buccaneer comes from the word boucan.\n",
+        "A boucan is a wooden frame used for cooking meet.\n",
+        "Buccaneer is the West Indies name for a pirate.\n"
+    };
+
+    int fd = open("buccaneer.txt", O_WRONLY | O_CREAT | O_TRUNC);
+    if (fd == -1) {
+        perror("open");
+        return 1;
+    }
+
+    // fill out three iovec structures
+    for (int i = 0; i < 3; i++) {
+        iov[i].iov_base = buf[i];
+        iov[i].iov_len = strlen(buf[i]) + 1;
+    }
+
+    // with a single call, write them all out
+    ssize_t nr = writev(fd, iov, 3);
+    if (nr == -1) {
+        perror("writev");
+        return 1;
+    }
+
+    printf("wrote %lu bytes\n", nr);
+
+    if (close(fd)) {
+        perror("close");
+        return 1;
+    }
+
+    return 0;
+}