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1. Top results related to what are protocols in operating systems in c

   • What are the Protocols in Objective-C?

     Objective-C is a language versatile and sophisticated enough for iOS and Mac OS GUI programming. One Objective-C feature that can be called both flexible and dynamic is the use of protocols. Protocols help in the creation of interfaces where a class implementation needs to follow a set of methods and properties.

     Table of Content

     • What are the Protocols in Objective-C?
     • Types of Protocols in Objective-C
     • Syntax and Keywords
     • Examples
     • Conclusion

     What are the Protocols in Objective-C?A protocol is a normative approach to constrain a set of classes that may require a common interface, for instance, delegates, data sources, and observers.

     • This approach can also integrate secondary, or multiple, inheritance which is not permitted when working with Cocoa classes.
     • A single class can be responsible for multiple protocols, which means it can easily adapt the behavior of several other classes without necessarily subclassing these classes.

     Types of Protocols in Objective-CThere are two types of protocols in Objective-C, formal and informal protocols.

     Formal ProtocolsIn the formal protocol declaration, the name of the protocol and its methods and properties are used after the prefix @protocol. Protocols declare methods and properties with modifiers, like @required or @optional, to indicate the needed implementation by the classes that accept the protocol. After this, the @end statement must appear. It marks the end of the protocol declaration.

     For instance, the below code defines an arbitrary protocol called PrintProtocolDelegate, specifically, in which it declares a single necessary method called processCompleted.

     -@protocol PrintProtocolDelegate@requiredvoid processCompleted...

     • “Categories are a way of adding methods to the existing class without its subclassing” – groups methods that don’t add new behaviors to the original class.
     • A non-official protocol is a list of rules that are not required by classes to implement, but they are expected to be available while the classes are under execution.
     • They are however checked by the compiler, therefore programs may contain the methods even though the particular classes that are accepting them do not implement them at all.
     • They don’t correspond to the function declarations as returned by the header files so they are substantially more difficult to identify and apply.
     • These collisions result from the repeated use of names that are the same but possess various signatures or connotations.

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     1/5

   • What are the meanings of parameters passed to sem_init() in Semaphores(Operating Systems)?

     Top Answer

     Answered Nov 16, 2016 · 1 votes

     Always try to read Linux documentation(man <command or system_call>) for these type of doubts.

     for your case man sem_init

     sem_init() initializes the unnamed semaphore at the address pointed to by sem. The value argument specifies the initial value for the semaphore.

     web link of the man pages

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     2/5

   • What are Ring 0 and Ring 3 in the context of operating systems?

     Top Answer

     Answered May 29, 2021 · 146 votes

     Linux x86 ring usage overview

     Understanding how rings are used in Linux will give you a good idea of what they are designed for.

     In x86 protected mode, the CPU is always in one of 4 rings. The Linux kernel only uses 0 and 3:

     • 0 for kernel
     • 3 for users

     This is the most hard and fast definition of kernel vs userland.

     Why Linux does not use rings 1 and 2: CPU Privilege Rings: Why rings 1 and 2 aren't used?

     How is the current ring determined?

     The current ring is selected by a combination of:

     • global descriptor table: a in-memory table of GDT entries, and each entry has a field Privl which encodes the ring.The LGDT instruction sets the address to the current descriptor table.See also: http://wiki.osdev.org/Global_Descriptor_Table
     • the segment registers CS, DS, etc., which point to the index of an entry in the GDT.For example, CS = 0 means the first entry of the GDT is currently active for the executing code.

     What can each ring do?

     The CPU chip is physically built so that:

     • ring 0 can do anything
     • ring 3 cannot run several instructions and write to several registers, most notably: cannot change its own ring! Otherwise, it could set itself to ring 0 and rings would be useless.In other words, cannot modify the current segment descriptor, which determines the current ring.
     • cannot modify the page tables: How does x86 paging work?In other words, cannot modify the CR3 register, and paging itself prevents modification of the page tables.This prevents one process from seeing the memory of other processes for security / ease of programming reasons.
     • cannot register interrupt handlers. Those are configured by writing to memory locations, which is also prevented by paging.Handlers run in ring 0, and would break the security model.In other words, cannot use the LGDT and LIDT instructions.
     • cannot do IO instructions like in and out , and thus have arbitrary hardware accesses.Otherwise, for example, file permissions would be useless if any program could directly read from disk.More precisely thanks to Michael Petch: it is actually possible for the OS to allow IO instructions on ring 3, this is actually controlled by the Task state segment.What is not possible is for ring 3 to give itself permission to do so if it didn't have it in the first place.Linux always disallows it. See also: Why doesn't Linux use the hardware context switch via the TSS?

     How do programs and operating systems transition between rings?

     • when the CPU is turned on, it starts running the initial program in ring 0 (well kind of, but it is a good approximation). You can think this initial program as being the kernel (but it is normally a bootloader that then calls the kernel still in ring 0).
     • when a userland process wants the kernel to do something for it like write to a file, it uses an instruction that generates an interrupt such as int 0x80 or syscall to signal the kernel. x86-64 Linux syscall hello world example:

     .datahello_world: .ascii "hello world\n" hello_world_len = . - hello_world.text.global _start_start: /* write */ mov $1, %rax mov $1, %rdi mov $hello_world, %rsi mov $hello_world_len, %rdx syscall- /* exit */ mov $60, %rax mov $0, %rdi syscall-

     compile and run:

     as -o hello_world.o hello_world.Sld -o hello_world.out hello_world.o./hello_world.out-

     GitHub upstream.

     When this happens, the CPU calls an interrupt callback handler which the kernel registered at boot time. Here is a concrete baremetal example that registers a handler and uses it.

     This handler runs in ring 0, which decides if the kernel will allow this action, do the action, and restart the userland program in ring 3. x86_64

     • when the exec system call is used (or when the kernel will start /init), the kernel prepares the registers and memory of the new userland process, then it jumps to the entry point and switches the CPU to ring 3
     • If the program tries to do something naughty like write to a forbidden register or memory address (because of paging), the CPU also calls some kernel callback handler in ring 0.But since the userland was naughty, the kernel might kill the process this time, or give it a warning with a signal.
     • When the kernel boots, it setups a hardware clock with some fixed frequency, which generates interrupts periodically.This hardware clock generates interrupts that run ring 0, and allow it to schedule which userland processes to wake up.This way, scheduling can happen even if the processes are not making any system calls.

     What is the point of having multiple rings?

     There are two major advantages of separating kernel and userland:

     • it is easier to make programs as you are more certain one won't interfere with the other. E.g., one userland process does not have to worry about overwriting the memory of another program because of paging, nor about putting hardware in an invalid state for another process.
     • it is more secure. E.g. file permissions and memory separation could prevent a hacking app from reading your bank data. This supposes, of course, that you trust the kernel.

     How to play around with it?

     I've created a bare metal setup that should be a good way to manipulate rings directly: https://github.com/cirosantilli/x86-bare-metal-examples

     I didn't have the patience to make a userland example unfortunately, but I did go as far as paging setup, so userland should be feasible. I'd love to see a pull request.

     Alternatively, Linux kernel modules run in ring 0, so you can use them to try out privileged operations, e.g. read the control registers: How to access the control registers cr0,cr2,cr3 from a program? Getting segmentation fault

     Here is a convenient QEMU + Buildroot setup to try it out without killing your host.

     The downside of kernel modules is that other kthreads are running and could interfere with your experiments. But in theory you can take over all interrupt handlers with your kernel module and own the system, that would be an interesting project actually.

     Negative rings

     While negative rings are not actually referenced in the Intel manual, there are actually CPU modes which have further capabilities than ring 0 itself, and so are a good fit for the "negative ring" name.

     One example is the hypervisor mode used in virtualization.

     For further details see:

     • https://security.stackexchange.com/questions/129098/what-is-protection-ring-1
     • https://security.stackexchange.com/questions/216527/ring-3-exploits-and-existence-of-other-rings

     ARM

     In ARM, the rings are called Exception Levels instead, but the main ideas remain the same.

     There exist 4 exception levels in ARMv8, commonly used as:

     .text.global _start_start: /* write */ mov x0, 1 ldr x1, =msg ldr x2, =len mov x8, 64 svc 0- /* exit */ mov x0, 0 mov x8, 93 svc 0msg: .ascii "hello syscall v8\n"len = . - msg-

     sudo apt-get install qemu-user gcc-arm-linux-gnueabihfarm-linux-gnueabihf-as -o hello.o hello.Sarm-linux-gnueabihf-ld -o hello hello.oqemu-arm hello-

     • EL0: userland
     • EL1: kernel ("supervisor" in ARM terminology).Entered with the svc instruction (SuperVisor Call), previously known as swi before unified assembly, which is the instruction used to make Linux system calls. Hello world ARMv8 example:hello.S .text.global _start_start: /* write */ mov x0, 1 ldr x1, =msg ldr x2, =len mov x8, 64 svc 0 /* exit */ mov x0, 0 mov x8, 93 svc 0msg: .ascii "hello syscall v8\n"len = . - msgGitHub upstream.Test it out with QEMU on Ubuntu 16.04: sudo apt-get install qemu-user gcc-arm-linux-gnueabihfarm-linux-gnueabihf-as -o hello.o hello.Sarm-linux-gnueabihf-ld -o hello hello.oqemu-arm helloHere is a concrete baremetal example that registers an SVC handler and does an SVC call.
     • EL2: hypervisors, for example Xen.Entered with the hvc instruction (HyperVisor Call).A hypervisor is to an OS, what an OS is to userland.For example, Xen allows you to run multiple OSes such as Linux or Windows on the same system at the same time, and it isolates the OSes from one another for security and ease of debug, just like Linux does for userland programs.Hypervisors are a key part of today's cloud infrastructure: they allow multiple servers to run on a single hardware, keeping hardware usage always close to 100% and saving a lot of money.AWS for example used Xen until 2017 when its move to KVM made the news.
     • EL3: yet another level. TODO example.Entered with the smc instruction (Secure Mode Call)

     The ARMv8 Architecture Reference Model DDI 0487C.a - Chapter D1 - The AArch64 System Level Programmer's Model - Figure D1-1 illustrates this beautifully:

     The ARM situation changed a bit with the advent of ARMv8.1 Virtualization Host Extensions (VHE). This extension allows the kernel to run in EL2 efficiently:

     VHE was created because in-Linux-kernel virtualization solutions such as KVM have gained ground over Xen (see e.g. AWS' move to KVM mentioned above), because most clients only need Linux VMs, and as you can imagine, being all in a single project, KVM is simpler and potentially more efficient than Xen. So now the host Linux kernel acts as the hypervisor in those cases.

     From the image we can see that when the bit E2H

     of register HCR_EL2

     equals 1, then VHE is enabled, and:

     • the Linux kernel runs in EL2 instead of EL1
     • when HCR_EL2.TGE == 1, we are a regular host userland program. Using sudo can destroy the host as usual.
     • when HCR_EL2.TGE == 0 we are a guest OS (e.g. when you run an Ubuntu OS inside QEMU KVM inside the host Ubuntu. Doing sudo cannot destroy the host unless there's a QEMU/host kernel bug.

     Note how ARM, maybe due to the benefit of hindsight, has a better naming convention for the privilege levels than x86, without the need for negative levels: 0 being the lower and 3 highest. Higher levels tend to be created more often than lower ones.

     The current EL can be queried with the MRS instruction: what is the current execution mode/exception level, etc?

     ARM does not require all exception levels to be present to allow for implementations that don't need the feature to save chip area. ARMv8 "Exception levels" says:

     An implementation might not include all of the Exception levels. All implementations must include EL0 and EL1. EL2 and EL3 are optional.

     QEMU for example defaults to EL1, but EL2 and EL3 can be enabled with command line options: qemu-system-aarch64 entering el1 when emulating a53 power up

     Code snippets tested on Ubuntu 18.10.

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   • operating systems memory management paging scheme in c

     Top Answer

     Answered Jun 03, 2015 · 2 votes

     The Solution is

     #include<stdio.h>#include<conio.h>#include<stdlib.h>void main(){ int mbt[50]; int i, j, k, pa, bs, bfree, bfree_mode, ps, js, var = 0, var2=0, jn, job;clrscr(); printf("\n\t\t PAGING\n"); printf("\n\t Enter the physical address space:"); scanf("%d",&pa); printf("\n\t Enter the Block size:"); scanf("%d",&bs); bfree = pa / bs; printf("\n\t the number of blocks are = %d\n",bfree); bfree_mode = bfree; for( i = 0 ; i < bfree ; i++ ) { mbt[i] = 0; } printf("How many jobs do you want to enter to the memory ?\n"); scanf("%d",&jn); for ( j = 0 ; j <= jn+2 ; j++ ) { printf("Enter %d Job size :\n",j+1); scanf("%d",&job); k = var; var = job / bs ; if (job % bs !=0) var +=1; if ( var <= bfree ) { var2 += var; for ( k ; k < var2 ; k++ ) { mbt[k] = j+1; } bfree -= var; printf("mbt[0] = OS Reserved!\n"); for ( i = 1 ; i < bfree_mode ; i++) printf("mbt[%d] = %d\n",i,mbt[i]); }else if ( var > bfree ) { printf("\nThe Memory is not enough for the %d Job",j+1); break; } }getch();}

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     4/5

   • In c#, what are the rules for defining a pure method?

     Top Answer

     Answered Jun 20, 2020 · 11 votes

     According to Wikipedia - Pure function:

     In computer programming, a function may be considered a pure function if both below statements about the function hold:

     • The function always evaluates the same result value given the same argument value(s). The function result value cannot depend on any hidden information or state that may change while program execution proceeds or between different executions of the program, nor can it depend on any external input from I/O devices (usually—see below).
     • Evaluation of the result does not cause any semantically observable side effect or output, such as mutation of mutable objects or output to I/O devices (usually—see below).

     The Microsoft documentation for the PureAttribute states this:

     Indicates that a type or method is pure, that is, it does not make any visible state changes.

     Microsofts description of what a pure method is is somewhat shorter and is missing one key piece, the fact that a pure method should always evaluate to the same result given the same input arguments.

     So is your method pure?

     • If you feed it the same rectangle and the same other argument values, it will always generate the same output, it does not use any other variables or information than what was provided to it through parameters.
     • Assuming that your usage of Rectangle is System.Drawing.Rectangle, which is a struct, then even though the method appears to be changing the rectangle it is only changing its own private copy of it, and thus you will not see any observable side effects of this method.
     • It does not use or change state (state is considered everything external to the argument values).

     So yes, this method is pure.

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     5/5

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2. kuleuven-diepenbeek.github.io › osc-course › ch2-c2.1: The C programming language :: Operating Systems and C

   kuleuven-diepenbeek.github.io › osc-course › ch2-c

   • Cached

   The UNIX, Windows and OSX kernels are fully written in C. The operating system of your cellphone, smartwatch or handheld all build on top of C. A huge amount of languages such as Java (JVM), Python, Ruby and PHP are first and foremost implemented in C. osc-1-files @wgroeneveld1.

3. www.geeksforgeeks.org › types-of-network-protocolsTypes of Network Protocols and Their Uses - GeeksforGeeks

   www.geeksforgeeks.org › types-of-network-protocols

   • Cached

   • What Is Network Protocol?
   • How Do Network Protocols Work?
   • Types of Network Protocols
   • Network Communication
   • Network Management
   • Network Security
   • Some Other Protocols

   A network protocol is a set of rules that govern data communication between different devices in the network. It determines what is being communicated, how it is being communicated, and when it is being communicated. It permits connected devices to communicate with each other, irrespective of internal and structural differences.

   See full list on geeksforgeeks.org

   It is essential to understand how devices communicate over a network by recognizing network protocols. The Open Systems Interconnection (OSI),the most widely used model, illustrates how computer systems interact with one another over a network. The communication mechanism between two network devices is shown by seven different layers in the OSI mod...

   See full list on geeksforgeeks.org

   In most cases, communication across a network like the Internetuses the OSI model. The OSI model has a total of seven layers. Secured connections, network management, and network communication are the three main tasks that the network protocolperforms. The purpose of protocols is to link different devices. The protocols can be broadly classified in...

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   Communication protocols are really important for the functioning of a network. They are so crucial that it is not possible to have computer networks without them. These protocols formally set out the rules and formats through which data is transferred. These protocols handle syntax, semantics, error detection, synchronization, and authentication. B...

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   These protocols assist in describing the procedures and policies that are used in monitoring, maintaining, and managing the computer network. These protocols also help in communicating these requirements across the network to ensure stable communication. Network management protocols can also be used for troubleshootingconnections between a host and...

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   These protocols secure the data in passage over a network. These protocols also determine how the network secures data from any unauthorized attempts to extract or review data. These protocols make sure that no unauthorized devices, users, or services can access the network data. Primarily, these protocols depend on encryption to secure data.

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   Internet Message Access Protocol

   1. ICMP protocol is used to retrieve message from the mail server. By using ICMP mail user can view and manage mails on his system.

   Session Initiation Protocol

   1. SIP is used in video, voice, and messaging application. This protocol is used to initiating, Managing, Terminating the session between two users while they are communicating.

   Real-Time Transport Protocol

   1. This protocol is used to forward audio, video over IP network. This protocol is used with SIP protocol to send audio, video at real-time.

   See full list on geeksforgeeks.org

4. People also ask

   What is a protocol in Computer Science?

   • Protocols usually include systems for error detection, correction, and encryption to assure data integrity and security during transmission. TCP, for example, uses sequence numbers and acknowledgment messages to ensure that data is delivered reliably. A Computer Science portal for geeks.

   Protocol and Standard in Computer Networks - GeeksforGeeks

   www.geeksforgeeks.org/protocol-and-standard-in-computer-networks/

   See all results for this question

   What is a network layer protocol?

   • It is known as a network layer protocol. In most cases, communication across a network like the Internet uses the OSI model. The OSI model has a total of seven layers. Secured connections, network management, and network communication are the three main tasks that the network protocol performs. The purpose of protocols is to link different devices.

   Types of Network Protocols and Their Uses - GeeksforGeeks

   www.geeksforgeeks.org/types-of-network-protocols-and-their-uses/

   See all results for this question

   What is network communication protocol?

   • Below mentioned are some network communication protocol: Hypertext Transfer Protocol (HTTP) It is a layer 7 protocol that is designed for transferring a hypertext between two or more systems. HTTP works on a client-server model, most of the data sharing over the web is done through using HTTP. Transmission Control Protocol (TCP)

   Types of Network Protocols and Their Uses - GeeksforGeeks

   www.geeksforgeeks.org/types-of-network-protocols-and-their-uses/

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   What is a protocol stack?

   • The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. Some of these terms are used interchangeably but strictly speaking, the suite is the definition of the communication protocols, and the stack is the software implementation of them.

   Protocol stack - Wikipedia

   en.wikipedia.org/wiki/Protocol_stack

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5. www.freecodecamp.org › news › osi-model-networkingThe OSI Model – The 7 Layers of Networking Explained in Plain ...

   www.freecodecamp.org › news › osi-model-networking

   • Cached

   • Layer 1 is the physical layer. There’s a lot of technology in Layer 1 - everything from physical network devices, cabling, to how the cables hook up to the devices.
   • Layer 2 is the data link layer. Layer 2 defines how data is formatted for transmission, how much data can flow between nodes, for how long, and what to do when errors are detected in this flow.
   • Layer 3 is the network layer. This is where we send information between and across networks through the use of routers. Instead of just node-to-node communication, we can now do network-to-network communication.
   • Layer 4 is the transport layer. This where we dive into the nitty gritty specifics of the connection between two nodes and how information is transmitted between them.

6. www.geeksforgeeks.org › protocol-and-standard-inProtocol and Standard in Computer Networks - GeeksforGeeks

   www.geeksforgeeks.org › protocol-and-standard-in

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   Apr 8, 2024 · Protocols and standards enable secure and efficient computer network communication. They regulate data exchange, formatting, endpoints, and reliable device communication. These protocols and standards ensure network security and performance. Compliance can prevent data breaches and system breakdowns.

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8. en.wikipedia.org › wiki › Communication_protocolCommunication protocol - Wikipedia

   en.wikipedia.org › wiki › Communication_protocol

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   Protocols are to communication what algorithms or programming languages are to computations. Operating systems usually contain a set of cooperating processes that manipulate shared data to communicate with each other. This communication is governed by well-understood protocols, which can be embedded in the process code itself.

9. en.wikipedia.org › wiki › Protocol_stackProtocol stack - Wikipedia

   en.wikipedia.org › wiki › Protocol_stack

   • Cached

   The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. Some of these terms are used interchangeably but strictly speaking, the suite is the definition of the communication protocols, and the stack is the software implementation of them. [1]

10. www.khanacademy.org › open-standards-and-protocolsOpen protocol development (article) | Khan Academy

    www.khanacademy.org › open-standards-and-protocols

    • Cached

    The importance of being open. An open (nonproprietary) protocol is one that is not owned by any particular company and not limited to a particular company's products. The protocols in the Internet stack are open so that any computing device can follow the protocol to join the global network. You don't need to ask for permission to follow the ...