In a Unix system, several concurrent processes attend to different tasks. Each process
asks for system resources, be it computing power, memory, network connectivity, or
some other resource. The kernel is the big chunk of executable code in charge of handling
all such requests. Although the distinction between the different kernel tasks
isn’t always clearly marked, the kernel’s role can be split (as shown in Figure 1-1)
into the following parts:
Process management
The kernel is in charge of creating and destroying processes and handling their
connection to the outside world (input and output). Communication among different
processes (through signals, pipes, or interprocess communication primitives)
is basic to the overall system functionality and is also handled by the
kernel. In addition, the scheduler, which controls how processes share the CPU,
is part of process management. More generally, the kernel’s process management
activity implements the abstraction of several processes on top of a single
CPU or a few of them.
Memory management
The computer’s memory is a major resource, and the policy used to deal with it
is a critical one for system performance. The kernel builds up a virtual addressing
space for any and all processes on top of the limited available resources. The
different parts of the kernel interact with the memory-management subsystem
through a set of function calls, ranging from the simple malloc/free pair to much
more complex functionalities.
Filesystems
Unix is heavily based on the filesystem concept; almost everything in Unix can
be treated as a file. The kernel builds a structured filesystem on top of unstructured
hardware, and the resulting file abstraction is heavily used throughout the
whole system. In addition, Linux supports multiple filesystem types, that is, different
ways of organizing data on the physical medium. For example, disks may
be formatted with the Linux-standard ext3 filesystem, the commonly used FAT
filesystem or several others.
Device control
Almost every system operation eventually maps to a physical device. With the
exception of the processor, memory, and a very few other entities, any and all
device control operations are performed by code that is specific to the device
being addressed. That code is called a device driver. The kernel must have
embedded in it a device driver for every peripheral present on a system, from the
hard drive to the keyboard and the tape drive. This aspect of the kernel’s functions
is our primary interest in this book.
Networking
Networking must be managed by the operating system, because most network
operations are not specific to a process: incoming packets are asynchronous
events. The packets must be collected, identified, and dispatched before a process
takes care of them. The system is in charge of delivering data packets across
program and network interfaces, and it must control the execution of programs
according to their network activity. Additionally, all the routing and address resolution
issues are implemented within the kernel.
asks for system resources, be it computing power, memory, network connectivity, or
some other resource. The kernel is the big chunk of executable code in charge of handling
all such requests. Although the distinction between the different kernel tasks
isn’t always clearly marked, the kernel’s role can be split (as shown in Figure 1-1)
into the following parts:
Process management
The kernel is in charge of creating and destroying processes and handling their
connection to the outside world (input and output). Communication among different
processes (through signals, pipes, or interprocess communication primitives)
is basic to the overall system functionality and is also handled by the
kernel. In addition, the scheduler, which controls how processes share the CPU,
is part of process management. More generally, the kernel’s process management
activity implements the abstraction of several processes on top of a single
CPU or a few of them.
Memory management
The computer’s memory is a major resource, and the policy used to deal with it
is a critical one for system performance. The kernel builds up a virtual addressing
space for any and all processes on top of the limited available resources. The
different parts of the kernel interact with the memory-management subsystem
through a set of function calls, ranging from the simple malloc/free pair to much
more complex functionalities.
Filesystems
Unix is heavily based on the filesystem concept; almost everything in Unix can
be treated as a file. The kernel builds a structured filesystem on top of unstructured
hardware, and the resulting file abstraction is heavily used throughout the
whole system. In addition, Linux supports multiple filesystem types, that is, different
ways of organizing data on the physical medium. For example, disks may
be formatted with the Linux-standard ext3 filesystem, the commonly used FAT
filesystem or several others.
Device control
Almost every system operation eventually maps to a physical device. With the
exception of the processor, memory, and a very few other entities, any and all
device control operations are performed by code that is specific to the device
being addressed. That code is called a device driver. The kernel must have
embedded in it a device driver for every peripheral present on a system, from the
hard drive to the keyboard and the tape drive. This aspect of the kernel’s functions
is our primary interest in this book.
Networking
Networking must be managed by the operating system, because most network
operations are not specific to a process: incoming packets are asynchronous
events. The packets must be collected, identified, and dispatched before a process
takes care of them. The system is in charge of delivering data packets across
program and network interfaces, and it must control the execution of programs
according to their network activity. Additionally, all the routing and address resolution
issues are implemented within the kernel.
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