VFS File Operations & fops

The per-method contract the VFS imposes on struct file_operations implementations. Each fops callback has exact return semantics; the driver owns private_data lifetime, the struct file refcount, and the module refcount. Load references/README.md before writing a new .read / .write / .llseek / .open / .release / .unlocked_ioctl path.

When to use

• Writing, reviewing, or debugging a driver that installs a struct file_operations on a device node, char device, proc/debugfs file, or other VFS object.
• Implementing .open / .release, .read / .write, .llseek, .unlocked_ioctl / .compat_ioctl.
• Reasoning about private_data lifetime, struct file refcounting (get_file / fput), or the module-unloaded-while-open class of bugs.
• Reviewing patches for CWE-416 / CWE-476 / CWE-252 regressions inside file-operation callbacks.