eCIFS In Depth
Copyright 2001, CodeFX
Software solutions for applications and appliances
ph: (619) 269-4274
fax: (619) 269-4274
4545 Campus Ave. Suite #9
San Diego, CA 92116
Table of Contents
New CIFS markets.
eCIFS technical details.
Microsoft and Windows are either trademarks or registered trademarks
of Microsoft Corporation. CodeFX is not affiliated with Microsoft Corporation.
All other trademarks referenced within this document are property of their respective owners.
CIFS, or the Common Internet File System, is a network protocol that allows computers to share files and printers. There are two distinct entities involved when a file or printer is shared: a client and a server. For sharing to occur, a user specifies a file folder or printer to be shared on the server. Sometime in the future, the client can then establish a connection and logon to the server by sending CIFS packets that indicate which resource the client wants access to, as well as the client’s username/password combination. The client can then work with files or use the printer on the remote computer. All of these negotiations are accomplished using the CIFS protocol.
CIFS is an extremely popular network protocol because almost all Microsoft operating systems use CIFS for file and printer sharing. Microsoft includes CIFS client and server capabilities in Windows For Workgroups, Windows 95, Windows 98, Windows ME, Windows NT 3.5, Windows NT 4.0, and Windows 2000. In addition, almost all variants of the UNIX operating system can become CIFS capable using the Samba software package. For these reasons, CIFS is used extensively in home and enterprise environments for file and printer sharing.
Several developments and trends over the past 5 years have created new potential markets for the CIFS protocol. These developments and trends are listed and analyzed below.
Because of these trends, a new breed of CIFS-enabled electronic devices could offer exciting new services to the consumer. A CIFS-enabled device can gain access to any files or printers that are shared on the Internet or LAN. In order to better understand some of the possibilities with CIFS-enabled consumer electronics, a few hypothetical products are listed below.
Media terminal: A home stereo component could be manufactured which plays modern media file types, such as MP3 music and MPEG encoded video. The device could use local, on-board storage to hold these new multimedia formats, however, it would be more cost effective and elegant to leave the files on a local area network PC and simply use the CIFS protocol to gain access to the media. Utilizing IP connectivity and the CIFS protocol, the device can do away with storage, download, and transfer of the actual media files. The result is less engineering costs, easy storage upgrades (by adding more hard drive capacity to the PC), and centralized storage of all multimedia content. The new device simply acts as a thin client accessing and playing any multimedia content the user requests.
PDA feature: As PDA’s are more and more commonly being used to access files on a PC, a CIFS client could be added to the PDA to allow the exploration of the PC file system directly from the PDA. This would allow the end user much more flexibility and greater ease of use.
In addition to these examples, there are many other potential uses for CIFS running on an embedded device. Cell phones could use a CIFS client to wirelessly access files located on a desktop PC or to download Outlook Express address book information in order to reprogram the cell phone’s address database. Fax machines could use CIFS to allow users to specify files on the network to fax. A video game console could completely do away with cartridges or CD-ROM’s by instead using CIFS to transfer a game from a PC on the network to the gaming console. CIFS opens a new world of creative, exciting and innovative applications for the connected consumer electronic device market.
eCIFS is a portable, ‘C’ source code CIFS client implementation that CodeFX has designed, developed, and debugged. CodeFX sells eCIFS to companies and individuals who are enabling their smart devices and appliances to communicate on a CIFS network – essentially allowing that device access to any shared files and printers on the LAN.
Entry into the new CIFS markets specified above is best accomplished via the eCIFS product. The following list details the benefits of using eCIFS to penetrate these new markets.
Because of these reasons, CodeFX feels that eCIFS will be a mainstream tool for developers of smart devices/appliances in the 21st century. A quick, clean, and easy entry into the CIFS connected appliance market is best accomplished via the eCIFS product.
The eCIFS product is written in the ‘C’ programming language and presents a simple and clean ‘C’ API to the programmer. eCIFS keeps all of the CIFS packet exchanges behind the scenes and only allows basic file operations similar to “fopen” and “fread” to be called from the API. In using these function calls, a software developer does not have to be very familiar with the CIFS protocol and can concentrate on other programming tasks. A few typical API function calls are presented in Appendix A.
Most eCIFS API function calls can be either blocking or non-blocking. This allows a great deal of flexibility for the programmer. If desired, a given function, such as a remote file read, can block until all the data has been acquired. However, if the calling thread cannot block, a non-blocking flag can be passed to the read function that allows the calling thread to continue execution, and a programmer specified callback function would execute when the read is completely finished.
In order for eCIFS to accomplish system-specific functionality (such as TCP/IP networking, inter-process communication, and thread spawning), an abstraction layer is used which keeps all of the system-specific utility functions wrapped in generic function calls. In order to port the eCIFS product to a new system, the actual contents of the generic function calls are changed to match the function calls of the new system (this porting process can be done by CodeFX or in-house engineers). These generic function calls are all contained in 4 porting files, and the bulk of the eCIFS source code is never modified in any way.
The CIFS protocol requires the TCP/IP network protocol for delivery of CIFS packets. eCIFS does not include a TCP/IP network stack, and therefore, the desired product must already have TCP/IP functionality. To better understand where the eCIFS protocol fits into a networked environment, the diagram below is included. The network protocols with the green background (NetBIOS and CIFS) are provided by the eCIFS implementation.
Figure 1 - eCIFS implements protocols in green
To promote future compatibility, eCIFS uses the latest CIFS dialect, titled “NT LM 0.12”, and is also capable of challenge-response password encryption. The eCIFS code is tested and compatible with Windows 95, Windows 98, Windows ME, Windows NT 4.0, Windows 2000, and the Samba Unix CIFS package. Because Microsoft makes new operating system releases backwards compatible with their previous operating systems, the eCIFS code should interoperate with future Microsoft operating systems with no problems.
This concludes the discussion of the eCIFS product. More information on the CIFS protocol in general can be found in the CodeFX whitepaper titled “CIFS Explained”. This document is available at www.codefx.com/products.htm. Questions or comments are welcomed and should be emailed to firstname.lastname@example.org.
THIS PAPER IS PROVIDED BY CodeFX FOR INFORMATIONAL PURPOSES ONLY. THE MARKETING INFORMATION CONTAINED HEREIN IS THE OPINION OF CodexFX. OPINIONS ARE PRONE TO ERROR AND SHOULD NOT BE USED AS THE SOLE BASIS FOR DECISION OR ACTION.
A small subset of the eCIFS API is listed below. Please note that the call_mode argument can be either EC__BLOCK (for blocking calls), or EC__NOBLOCK (for non blocking calls).
int Ec__ca_fopen(int call_mode, Ec__ca_conn *conn, Ec__ca_fdata *f_data,
char *name, int access_mode, int opts, int share_mode, int magic_num);
int Ec__ca_fread(int call_mode, Ec__ca_conn *conn, Ec__ca_fdata *f_data,
void *buf, u_int32_t offset, u_int32_t *size, int magic_num);
int Ec__ca_fwrite(int call_mode, Ec__ca_conn *conn, Ec__ca_fdata *f_data,
void *buf, u_int32_t *size, int magic_num);