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Full Discussion: System calls?
Top Forums UNIX for Dummies Questions & Answers System calls? Post 302069461 by Perderabo on Sunday 26th of March 2006 08:12:06 PM
Old 03-26-2006
This could be someone reading a book and getting lost in the terminology. So I will give the poster the benefit of doubt and assume that the rule against homework questions is not being broken.

Yes those 6 functions are usually considered "primitive". Over the years the open system call has gained more power. creat can now be implemented as a call to open. That is the only questionable one among the group. If you look at all of the system calls you will see that a lot of them are involved in i/o. You could use the term "i/o system calls" to describe that set. But you would need some other term like, "non i/o system calls" for stuff like gettimeofday, setuid, etc. Reasonable minds could disagree over which class gets certain system calls like exit and exec.
 

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dup(2)								System Calls Manual							    dup(2)

Name
       dup, dup2 - duplicate an open file descriptor

Syntax
       newd = dup(oldd)
       int newd, oldd;

       dup2(oldd, newd)
       int oldd, newd;

Description
       The  system  call  duplicates  an  existing  object descriptor.	The argument oldd is a small non-negative integer index in the per-process
       descriptor table.  The value must be less than the size of the table, which is returned by The new descriptor, newd, returned by  the  call
       is the lowest numbered descriptor that is not currently in use by the process.

       The object referenced by the descriptor does not distinguish between references using oldd and newd in any way.	Thus, if newd and oldd are
       duplicate references to an open file, and calls all move a single pointer into the file.  If a separate pointer into the file is desired, a
       different object reference to the file must be obtained by issuing an additional call.

       In the second form of the call, specify the value of newd needed. If this descriptor is already in use, the descriptor is first deallocated
       as if a call had been done.

Return Values
       The value -1 is returned if an error occurs in either call.  The external variable errno indicates the cause of the error.

Diagnostics
       The and system calls fail under the following conditions:

       [EBADF]	      The oldd or newd is not a valid active descriptor.

       [EMFILE]       Too many descriptors are active.

       [EINTR]	      The or function was terminated prematurely by a signal.

See Also
       accept(2), close(2), getdtablesize(2), lseek(2), open(2), pipe(2), read(2), socket(2), socketpair(2), write(2)

																	    dup(2)
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