Page 294 - DCAP403_Operating System

Unit 13: Case Study: Linux

of protocol operations. This is a set of routines, each of which performs a a particular operation Notes

specific to that address family. The registered protocol operations are kept in the pops vector, a
vector of pointers to proto_ops data structures.
The proto_ops data structure consists of the address family type and a set of pointers to socket

operation routines specific to a particular address family. The pops vector is indexed by the

address family identifier, for example the Internet address family identifier (AF_INET is 2).
Figure 13.14: Linux BSD Socket Data Structures
files_struct
count
close_on_exec
open_fs
fd[0] file
fd[1] f_mode
f_pcs
f_flags
fd[255] f_count
f_ownet
BSD Socket
f_op File Operations
f_inode 1seek
read
f_version
write
select
inode
ioctl
fasync
socket
type
SOCK_STREAM
ops Address Family
data socket operations

sock
type SOCK_STREAM
protocol
socket

13.9.4 The INET Socket Layer

The INET socket layer supports the internet address family which contains the TCP/IP protocols.
As discussed above, these protocols are layered, one protocol using the services of another.
Linux’s TCP/IP code and data structures refl ect this layering. Its interface with the BSD socket
layer is through the set of Internet address family socket operations which it registers with the
BSD socket layer during network initialization. These are kept in the pops vector along with
the other registered address families. The BSD socket layer calls the INET layer socket support
routines from the registered INET proto_ops data structure to perform work for it. For example
a BSD socket create request that gives the address family as INET will use the underlying INET
socket create function. The BSD socket layer passes the socket data structure representing the
BSD socket to the INET layer in each of these operations. Rather than clutter the BSD socket wiht
TCP/IP specific information, the INET socket layer uses its own data structure, the sock which it

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