This trace is specific to Linux's read(2) interface at a useful conceptual level. Exact functions and device paths vary by kernel version, file type, filesystem, and whether data is already cached.
1. Userspace prepares the call
The program passes a file descriptor, destination buffer, and byte count to the C library wrapper. The wrapper arranges the syscall number and arguments according to the platform ABI, then executes the architecture's syscall instruction.
2. The processor enters the kernel
The CPU changes privilege level and transfers control to a kernel entry path. The kernel validates the request and looks up the open file description associated with the calling process's descriptor. A descriptor is a process-local handle, not a disk block address.
3. The file system supplies bytes
The virtual file system dispatches through the file's operations. A regular-file read may copy bytes from page-cache pages if they are present. If data is absent, the kernel and storage stack may issue I/O and put the task to sleep until data arrives. Pipes, sockets, devices, and special files can follow different paths.
4. Return a result
The kernel copies available bytes into the userspace buffer and returns the number copied. A successful read may be shorter than requested. Zero commonly means end of file; a negative result represented through the C library indicates an error. The caller must handle partial reads when its protocol requires a complete buffer.
The Linux read(2) manual defines the observable API contract. It does not promise that every read reaches physical storage.