Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucdavis!iris!kerchen
From: kerchen@iris.ucdavis.edu (Paul Kerchen)
Newsgroups: comp.unix.wizards
Subject: syscall(2)--a summary of responses
Summary: good reasons
Keywords: system calls, syscall(2)
Message-ID: <3774@ucdavis.ucdavis.edu>
Date: 7 Mar 89 23:44:04 GMT
Sender: uucp@ucdavis.ucdavis.edu
Reply-To: kerchen@iris.ucdavis.edu (Paul Kerchen)
Distribution: usa
Organization: U.C. Davis - Department of Electrical Engineering and Computer Science
Lines: 29


At the request of several people, here's a brief list of reasons supporting 
the need for syscall(2).  For those who are tired of this discussion,
hit 'n' now! :-}



Compelling reasons for the use of syscall(2):

1) Changing the functionality of a system call, keeping track of the number
	of times a call is made, or intervening before a call is made.
2) Testing new system calls before adding them to the kernel.
3) Simulating system calls.
4) Backwards compatibility to phased-out system calls (eg. stty vs. ioctl).
5) Certain other, specific applications.

Note: On some OS's (like SunOS), syscall(2) is just another function, while
on others (like Ultrix V2.2), syscall(2) is the only mechanism for making
system calls (ie. all other calls eventually call syscall(2) to do the actual
call).  Therefore, syscall(2) really is a necessity for some systems.  For
a more verbose listing of reasons, send me e-mail and I'll send you a 
trimmed down concatenation of all the responses I've received (provided
the mailer doesn't bounce 'em).  That is, I'll send you a list of verbatim 
responses without all of the extra header junk.




Paul Kerchen				| kerchen@iris.ucdavis.edu