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Full Discussion: Difference between system calls and normal functions in C
Top Forums Programming Difference between system calls and normal functions in C Post 302571424 by jim mcnamara on Monday 7th of November 2011 10:37:13 AM
Old 11-07-2011
chmod() also is used to change permissions.

Depending on the UNIX, the standard system calls (ones required by POSIX standards)
all present the same interface for us to call. All open() calls present the same semantics for us to use, for example, on any standards conforming system. As long as the UNIX follows POSIX standards your code is portable.

What happens inside the call is never standard. Some UNIX implementions have a list of "syscalls" with entry points (function pointers). If you understand how those entry points work, you can call them directly - which you should only do in very clearly defined cases, such as system programming just for that OS and just for that version of the OS. Other systems do not support the idea of syscalls.

Then there is the system API. This is stuff which is specific to a particular OS. So it can't be used on another kinds of UNIX. Linux has loads of these. All UNIXes have them.
Sometimes these specific calls will "piggyback" on standard calls by adding extra flags or options. ioctl() often does this. So if you know everything about ioctl on HPUX, when you get to Linux there are some new things to learn.

An example of an altogether different function is Solaris' ustat(). Solaris also has seemingly odd "devices" like doors, that some other systems have not had up until now, so ioctl has to support them on Solaris. Linux had a door implementation, which I think is now deprecated. BTW all devices on a UNIX box are presented as files. No matter how odd the device might be, so there has to be a way to play with them.
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LEARN ABOUT DEBIAN

aoe-interfaces

aoe-interfaces(8)					      System Manager's Manual						 aoe-interfaces(8)

NAME

       aoe-interfaces - restrict aoe driver to specified network interfaces

SYNOPSIS

       aoe-interfaces [dev1] [dev2 ...]
       aoe-interfaces -c

DESCRIPTION

       The  aoe-interfaces command tells the aoe driver to ignore ATA over Ethernet (AoE) traffic on all but the specified network interfaces.	It
       is analogous to the aoe_iflist module load option.

       If neither the aoe_iflist module load option nor the aoe-interfaces command are used, the aoe driver will use any network interface for AoE
       traffic.   Using  aoe-interfaces  to limit AoE to only trusted networks prevents the case where a rogue AoE target appears on a public net-
       work, diverting data from the legitimate AoE target.  Such an imposter target effectively corrupts the data on the legitimate target.

       If the aoe driver is a module, then calling aoe-interfaces without arguments will display the current interfaces list.  If it  hasn't  been
       set then the output will be blank.

       It's good to run the aoe-discover command after setting the AoE interfaces list.

OPTIONS

       -c     The -c flag will clear the interface access list, permitting any interface to be used.

EXAMPLE

       In  this  example, the root user on a host named nai loads the aoe module with only eth0 allowable for AoE traffic.  After remembering that
       shelf 7 is on eth3, this sysadmin uses aoe-interfaces to add eth3 to the list of allowable network interfaces and then  calls  aoe-discover
       to ask the aoe driver to look for new AoE devices.

	      nai:~# modprobe aoe aoe_iflist="eth0"
	      nai:~# aoe-stat
		 e10.9		  eth0		    up
	      nai:~# aoe-interfaces eth0 eth3
	      nai:~# aoe-discover
	      nai:~# aoe-stat
		  e7.0		  eth3		    up
		  e7.1		  eth3		    up
		  e7.2		  eth3		    up
		  e7.3		  eth3		    up
		  e7.4		  eth3		    up
		  e7.5		  eth3		    up
		  e7.6		  eth3		    up
		  e7.7		  eth3		    up
		  e7.8		  eth3		    up
		  e7.9		  eth3		    up
		 e10.9		  eth0		    up
	      nai:~# aoe-interfaces
	      eth0 eth3

SEE ALSO

       aoe-discover(8), aoe-stat(8), aoetools(8).

AUTHOR

       Ed L. Cashin (ecashin@coraid.com)

																 aoe-interfaces(8)
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