COMP 3000 Essay 1 2010 Question 2 - Revision history

Soma: Unprotected "COMP 3000 Essay 1 2010 Question 2"

2010-11-08T15:32:35Z

Unprotected "COMP 3000 Essay 1 2010 Question 2"

← Older revision	Revision as of 15:32, 8 November 2010
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Soma: /* Process Control Calls */

2010-10-17T16:51:08Z

Process Control Calls

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	each of these are called when different arguments are given.		each of these are called when different arguments are given.

	The following are the definitions for the these system calls as described by this [http://www.di.uevora.pt/~lmr/syscalls.html]		The following are the definitions for the these system calls as described by this [http://www.di.uevora.pt/~lmr/syscalls.html] '''NOTE: only execve() is an actual system call. The rest are C library functions that wrap execve(). This is true for UNIX and Linux. --Anil'''

	''execl()'': Takes the path name of an executable program (binary file) as its first argument. The rest of the arguments are a list of command		''execl()'': Takes the path name of an executable program (binary file) as its first argument. The rest of the arguments are a list of command

Soma: /* Information Maintenance Calls */

2010-10-17T16:47:57Z

Information Maintenance Calls

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	== Information Maintenance Calls==		== Information Maintenance Calls==
	Information maintenance calls are system calls that return the computers personal information back to the user or change it completely. These type of calls can be split up into three groups get/set time or date, get/set system data and get/set process, file, or device attributes. To fully understand the difference between Linux and UNIX in ~~regrades~~ to system calls, one must explore the three sub-types of information maintenance calls and see how they have changed over time.		Information maintenance calls are system calls that return the computers personal information back to the user or change it completely. These type of calls can be split up into three groups get/set time or date, get/set system data and get/set process, file, or device attributes. To fully understand the difference between Linux and UNIX in regards to system calls, one must explore the three sub-types of information maintenance calls and see how they have changed over time.

	The first sub type is Get/set of time and/or date. In Linux, this can be done by a few different system calls, there are: 'gettimeofday' to get the time, 'settimeofday' to set it, 'time' returns the time in seconds and a few other ones like 'ftime'.In the earliest versions UNIX the used the system call was 'stime', which was used to interact with time and dates. 'stime' could return the time and date and sets the system’s idea of the time and date by altering the seconds. 'stime' is still being used by Linux because it is successful, unlike 'settimeofday', which was created to change timezones (tz_dsttime) as well as the time but each occurrence of this field call in the kernel source (apart from declaration) is a bug thus failing.		The first sub type is Get/set of time and/or date. In Linux, this can be done by a few different system calls, there are: 'gettimeofday' to get the time, 'settimeofday' to set it, 'time' returns the time in seconds and a few other ones like 'ftime'.In the earliest versions UNIX the used the system call was 'stime', which was used to interact with time and dates. 'stime' could return the time and date and sets the system’s idea of the time and date by altering the seconds. 'stime' is still being used by Linux because it is successful, unlike 'settimeofday', which was created to change timezones (tz_dsttime) as well as the time but each occurrence of this field call in the kernel source (apart from declaration) is a bug thus failing.

Soma: /* Answer */

2010-10-17T15:50:43Z

Answer

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	=Answer=		=Answer=

	A system call is a mean by which programs in the user space can access kernel services. Systems calls vary from operating system to operating system, although the underlying concepts tends to be the same. In general, a process is not supposed to be able to access the kernel directly. It can't access kernel memory and it can't call kernel functions. ~~When the CPU prevents a process from accessing the kernel, this prevention is commonly known as, the protected mode. On the other hand, system~~ calls are an exception to this rule. ~~For example, older~~ x86 processors used an interrupt mechanism to go from user-space to kernel-space, but newer processor (PentiumII+) provided instructions that optimize this transition using sysenter and sysexit instructions (Hayward, Mike. Intel P6 vs P7 system call performance. [http://lkml.org/lkml/2002/12/9/13], December 9, 2002). ~~All system calls are small programs built using the C programming language.~~		A system call is a mean by which programs in the user space can access kernel services. Systems calls vary from operating system to operating system, although the underlying concepts tends to be the same. In general, a process is not supposed to be able to access the kernel directly. It can't access kernel memory and it can't call kernel functions. System calls are an exception to this rule. Older x86 processors used an interrupt mechanism to go from user-space to kernel-space, but newer processor (PentiumII+) provided instructions that optimize this transition using sysenter and sysexit instructions (Hayward, Mike. Intel P6 vs P7 system call performance. [http://lkml.org/lkml/2002/12/9/13], December 9, 2002).

	The Unix and Linux systems calls are roughly grouped into 6 major categories: file management, device management, information maintenance, process control, communications and miscellaneous calls. The miscellaneous calls are all the ones that don’t really fit in the other categories, like system calls dealing with errors. Today, the Unix and Linux operating system contains hundreds of system calls but in general, they all came from the 35 system calls that came with one of the original UNIX OS in the early 70s. In the next paragraphs, we’re going to describe the various system calls in each of the categories mentioned above, their evolution through history (major changes in functionality) and a comparison with the earliest versions of UNIX.		The Unix and Linux systems calls are roughly grouped into 6 major categories: file management, device management, information maintenance, process control, communications and miscellaneous calls. The miscellaneous calls are all the ones that don’t really fit in the other categories, like system calls dealing with errors. Today, the Unix and Linux operating system contains hundreds of system calls but in general, they all came from the 35 system calls that came with one of the original UNIX OS in the early 70s. In the next paragraphs, we’re going to describe the various system calls in each of the categories mentioned above, their evolution through history (major changes in functionality) and a comparison with the earliest versions of UNIX.

Soma: Protected "COMP 3000 Essay 1 2010 Question 2" ([edit=sysop] (indefinite) [move=sysop] (indefinite))

2010-10-15T13:34:29Z

Protected "COMP 3000 Essay 1 2010 Question 2" ([edit=sysop] (indefinite) [move=sysop] (indefinite))

← Older revision	Revision as of 13:34, 15 October 2010
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Rarteaga: /* Miscellaneous System Calls */

2010-10-15T11:05:11Z

Miscellaneous System Calls

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	Lastly, there are some system calls which overlap and can be considered in a specific category or mentioned within the Miscellaneous System Calls. Referring to the ``3rd edition, Modern Operating Systems`` textbook, the command, ``chmod`` described above in File Management Calls is considered Miscellaneous. Similarly, the kill() command is mentioned as a Miscellaneous System Call. Hence, it is difficult to decifer whether a system call can be placed into a specific category or simply placed in the ``Other`` bin.		Lastly, there are some system calls which overlap and can be considered in a specific category or mentioned within the Miscellaneous System Calls. Referring to the ``3rd edition, Modern Operating Systems`` textbook, the command, ``chmod`` described above in File Management Calls is considered Miscellaneous. Similarly, the kill() command is mentioned as a Miscellaneous System Call. Hence, it is difficult to decifer whether a system call can be placed into a specific category or simply placed in the ``Other`` bin.


	Most of the older OS like Unix, had majority of system calls, but the newer(or modern) OS have more to offer in terms of quantity of system calls. With changes to the syntax a fair bit, it`s not too difficult to transfer over. This is in result of the programmers desiring a portable set of original system calls. Although not all are portable, they try to keep most portable such that less work is involved trying to go from one system to a newer system.		Most of the older OS like Unix, had majority of system calls, but the newer(or modern) OS have more to offer in terms of quantity of system calls. With changes to the syntax a fair bit, it`s not too difficult to transfer over. This is in result of the programmers desiring a portable set of original system calls. Although not all are portable, they try to keep most portable such that less work is involved trying to go from one system to a newer system.

Rarteaga: /* Miscellaneous System Calls */

2010-10-15T10:21:53Z

Miscellaneous System Calls

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	Lastly, there are some system calls which overlap and can be considered in a specific category or mentioned within the Miscellaneous System Calls. Referring to the ``3rd edition, Modern Operating Systems`` textbook, the command, ``chmod`` described above in File Management Calls is considered Miscellaneous. Similarly, the kill() command is mentioned as a Miscellaneous System Call. Hence, it is difficult to decifer whether a system call can be placed into a specific category or simply placed in the ``Other`` bin.		Lastly, there are some system calls which overlap and can be considered in a specific category or mentioned within the Miscellaneous System Calls. Referring to the ``3rd edition, Modern Operating Systems`` textbook, the command, ``chmod`` described above in File Management Calls is considered Miscellaneous. Similarly, the kill() command is mentioned as a Miscellaneous System Call. Hence, it is difficult to decifer whether a system call can be placed into a specific category or simply placed in the ``Other`` bin.

			Most of the older OS like Unix, had majority of system calls, but the newer(or modern) OS have more to offer in terms of quantity of system calls. With changes to the syntax a fair bit, it`s not too difficult to transfer over. This is in result of the programmers desiring a portable set of original system calls. Although not all are portable, they try to keep most portable such that less work is involved trying to go from one system to a newer system.

	== Conclusion ==		== Conclusion ==

Rarteaga: /* Communications Calls */

2010-10-15T10:18:40Z

Communications Calls

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	Pipelines: ''pipe()'' The pipe() command consists of two components. int pipe (file_descriptors) & int file_descriptors[2]. File_descriptors is an array consisting of two parts as well. One is for reading the data, and the other is for writing the data. Both writing and reading data will read in sequential order along with fully completing it's task. I.e.) There are no partial writes, the pipe will write the whole data that was sent and complete the transmission. The same concept holds for the reading where it will be read all the way through before reading another pipe or new information coming into the pipe. A specially named pipe is FIFO. Standing First In First Out. It is accessed as part of a file system through idea of pipes.		Pipelines: ''pipe()'' The pipe() command consists of two components. int pipe (file_descriptors) & int file_descriptors[2]. File_descriptors is an array consisting of two parts as well. One is for reading the data, and the other is for writing the data. Both writing and reading data will read in sequential order along with fully completing it's task. I.e.) There are no partial writes, the pipe will write the whole data that was sent and complete the transmission. The same concept holds for the reading where it will be read all the way through before reading another pipe or new information coming into the pipe. A specially named pipe is FIFO. Standing for First In First Out. It is accessed as part of a file system through idea of pipes. Reflecting its name, it processes in a first come first serve basis. It deals with a process and once it is done with it completely, it moves onto the next process.

Sblais2: /* File Management Calls */

2010-10-15T10:15:06Z

File Management Calls

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	There is also system calls used to find, access and modify files. They are ''read'', ''write'', ''seek'' and ''stat''. These were also part of the first UNIX built. The ''read'' and ''write'' system calls allows to read and write from a file (assigned to a file descriptor). The only change was in the Unix System V release 4(SVR4) where a ''write'' call could be interrupted at anytime. The ''seek'' system calls is used to go to a specified position in a file. This calls used a 16 bit address offset. But this was replaced very quickly for ''lseek'' as early as SVR4. It allows the call to use 32 bit address ~~offsets~~ enabling the users more flexibility when ~~accessing~~ or writing to files especially for large ones. It is still used in modern Linux and Unix systems. As of now, developers are trying to implement ''lseek64'', a system call that will use 64 bit addresses. The ''stat'' system calls allows processes to get the status of a file. With SVR4, 2 other version of that system call were created: ''fstat'' and ''lstat''. They both do the same thing except ''lstat'' give the status of symbolic links and ''fstat'' give the status of a file specified by a file descriptor. Different operating systems will output different values to represent the state of a file. Since kernel 2.5.48, the stat returned a nanoseconds field in the file’s timestamp. With the release of 4.4BSD, two new system calls called ''statvfs'' and ''fstatvfs'' were introduced to provide information about a mounted file system. They both do the same thing except fstatvfs takes file descriptors as an argument. These calls are only used in an UNIX environment. In Linux, it has ''statfs'' and ''fstatfs'' to support that same call.		There is also system calls used to find, access and modify files. They are ''read'', ''write'', ''seek'' and ''stat''. These were also part of the first UNIX built. The ''read'' and ''write'' system calls allows to read and write from a file (assigned to a file descriptor). The only change was in the Unix System V release 4(SVR4) where a ''write'' call could be interrupted at anytime. The ''seek'' system calls is used to go to a specified position in a file. This calls used a 16 bit address to determine its position in a file(also called offset). But this was replaced very quickly for ''lseek'' as early as SVR4. It allows the call to use 32 bit address enabling the users more flexibility when reading or writing files especially for large ones. It is still used in modern Linux and Unix systems. As of now, developers are trying to implement ''lseek64'', a system call that will use 64 bit addresses. The ''stat'' system calls allows processes to get the status of a file. With SVR4, 2 other version of that system call were created: ''fstat'' and ''lstat''. They both do the same thing except ''lstat'' give the status of symbolic links and ''fstat'' give the status of a file specified by a file descriptor. Different operating systems will output different values to represent the state of a file. Since kernel 2.5.48, the stat returned a nanoseconds field in the file’s timestamp. With the release of 4.4BSD, two new system calls called ''statvfs'' and ''fstatvfs'' were introduced to provide information about a mounted file system. They both do the same thing except fstatvfs takes file descriptors as an argument. These calls are only used in an UNIX environment. In Linux, it has ''statfs'' and ''fstatfs'' to support that same call.

Rarteaga: /* References */

2010-10-15T10:12:19Z

References

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	Mendonça Rato, Luís Miguel,professor,university of evora. http://www.di.uevora.pt/~lmr/syscalls.html		Mendonça Rato, Luís Miguel,professor,university of evora. http://www.di.uevora.pt/~lmr/syscalls.html

			Tanenbaum, Andrew S. 3rd edition Modern Operating Systems.