Database Reference
In-Depth Information
form virtual organizations
30
that wish to share data securely across the wide
area. Some users require elaborate encryption and authorization mechanisms,
while others are content to identify users by simple host names. A suitable se-
curity mechanism for remote I/O must be flexible enough to accommodate all
of these scenarios without overly burdening the user that has simple needs. For
these reasons, we recommend the use of multiple authentication techniques
with full text subject names and access control lists.
4.5.2 Case Study: Parrot and Chirp
As a case study of a complete system for remote I/O, we present a discussion
of the tools Parrot and Chirp. Figure 4.5 shows how Parrot and Chirp work
together to provide seamless access to remote storage using the Unix I/O
interface. These tools have been used to provide remote I/O services for a
variety of applications in bioinformatics,
14
biometrics,
64
high-energy physics,
80
and molecular dynamics.
85
Parrot is a general-purpose tool for attaching applications to remote I/O
systems. Parrot does not require changes to applications or special privileges
to install, so it is well suited for use in large distributed systems such as com-
puting grids. Parrot works by trapping an application's system calls through
the debugging interface. System calls unrelated to I/O (such as
sbrk
) are
allowed to execute unmodified. System calls related to I/O (such as
open
,
read
, and
stat
) are handled by Parrot itself, and the results returned to the
application. Parrot is not limited to single process programs: It can run com-
plex multiprocess scripts and interpreted languages such as Perl and Java. An
interactive session using Parrot can be started by simply invoking:
% parrot tcsh
Parrot can be thought of as a user-level operating system. It contains multi-
ple drivers that implement access to remote services. Each driver is represented
Mount
list
Appl
Chirp protocol
Chirp
server
Trappe d
system calls
LAN or WAN
Parrot
Local
system calls
Grid
FTP
HTTP
RFIO
Chirp
File
system
Other remote services
Figure 4.5
Using Parrot and Chirp for remote I/O.
