Abstract:
An embodiment of a system, method and apparatus is disclosed. The system comprises a first processor that is in communication with a root existence table. The first processor is to check the root existence table to determine if a character is a root character. A second processor is in communication with a root active list. The second processor is to retrieve an entry that corresponds to the character and to associate a pointer with the entry. A third processor is in communication with the second processor and a tree structure. The third processor is to receive the pointer from the second processor and to maintain the tree and table structure.

Description:
RELATED APPLICATION 
   This application is a continuation application of U.S. application Ser. No. 10/172,486, U.S. Pat. No. 6,952,694, filed on Jun. 13, 2002, and priority is claimed thereof. 

   FIELD 
   Embodiments of the invention relate to identification of predetermined patterns in digital data and, more particularly, to a scheme for identifying a string of data using a multi-stage searching technique performed by multiple hardware components. 
   BACKGROUND 
   In order to expand networks to provide more information and services to more people and to a greater number of places, networks have become easier to use and more reliable. However, making the network operate smoothly requires a high degree of interoperability, scalability and platform independence. One aspect of network management is policy enforcement. Policy enforcement provides a way to give some types of traffic, such as real-time video, priority over other, less important traffic, such as e-mail. 
   Policy enforcement has been provided with general purpose computers, fixed-function appliances, and/or switches and routers. General purpose computers that provide policy enforcement typically include two or more network interface cards (NICs) that provide multiple connections to the network. Policy enforcement is provided by the processor of the general purpose computer. However, general purpose computers are not developed to perform high-speed operations on network packets. Because of this policy enforcement with general purpose computers is a bottleneck to network performance. 
   In an attempt to overcome the performance limitations of using general purpose computers for policy enforcement, fixed-function devices specifically designed to support policy enforcement have been developed. Typically, these fixed-function appliances have a processor and/or customized hardware and two or more NICs. While fixed-function appliances can be fast enough for some network operations, scalability is restricted. 
   Switches and routers have been used to provide policy enforcement. However, switches and routers typically do not have sufficient processing power to provide policy enforcement in addition to switching and routing functionality. The processors of the switches and routers must be used for both policy enforcement and for switching and/or routing functionality, which decreases network performance. Alternatively, switches and routers can be designed with more powerful processors, which increases the cost of the switches and routers. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings: 
       FIG. 1  illustrates an embodiment of a regular expression search engine; 
       FIG. 2  illustrates an exemplary state diagram of one embodiment of a finite state automation; 
       FIG. 3  illustrates an embodiment of a node tree; 
       FIG. 4  illustrates an embodiment of a root existence table; 
       FIG. 5  illustrates an embodiment of a root active list; 
       FIG. 6  illustrates an embodiment of a tree table structure; and 
       FIG. 7  illustrates an embodiment of an electronic system. 
   

   DETAILED DESCRIPTION 
   Methods and apparatuses for regular expression searching are described. In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. 
   Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     FIG. 1  illustrates an embodiment of a regular expression search engine  102 . In one embodiment, the search engine  102  is implemented as hardware, for example, as an application specific integrated circuit (ASIC) or as a programmable logic array (PLA). In alternate embodiments, the search engine can be implemented as a combination of hardware and software. 
   Incoming characters  170  are processed by root node processor  100 , which checks each incoming character to determine whether the character is a potential root character of a string of interest. As used herein a “string of interest” is a string of characters being searched for within a string of data. The data can be, for example, network packet, files, or any type of data. In general, when root node processor  100  identifies a character that is a potential root node, root node processor activates a finite state automaton (FSA) to identify whether or not the incoming data matches a particular string of interest. 
   In one embodiment, every character is checked to determine whether the character is a “^” character or a “\W” character. The “^” character indicates the beginning of a string or, if qualified by a “\n” character or a “\r” character, indicates the beginning of a line. The “\W” character indicates a non-alphanumeric character. 
   In one embodiment, a regular expression matches a string if any of the alternatives of the regular expression match. Alternatives are separated by the “|” character (i.e., the “vertical bar” character), and are evaluated left-to-right, stopping on the first complete match. An alternative matches if every item in the alternative matches in the order the items occur. 
   In one embodiment, an item includes an assertion and/or a quantified atom. Assertions are:
         “^” matches the beginning of the string (or line, if “$*” set).   “$” matches the end of the string (or line if “$*” set).   “\b” matches on word boundary (between “\w” and “\W”).   “\B” matches on non-word boundary.       

   In one embodiment, a quantified atom includes one of the following followed by a quantifier that indicates the number of times the atom must or may occur. If there is no quantifier, the atom must occur only once.
         “{n,m}” must occur at least n times but no more than m times.   “{n,}” must occur at least n times.   “{n}” must match exactly n times.   “*” must occur 0 or more times (same as “{0,}”).   “+” must occur 1 or more times (same as “{1,}”).   “?” must occur 0 or 1 time (same as “{0,1}”).       

   Acceptable atoms include the following. A regular expression in parentheses matches whatever the regular expression matches. A “.” matches any character except “\n”. A list of characters in square brackets (“[ ]”) matches one of a class of characters. A caret (“^”) at the beginning of the list negates the class. Character ranges may be indicated using “a-z” notation. 
   In one embodiment, a “backslash” character matches a special character or character class.
         “\b” indicates a backspace character class.   “\-” indicates a hyphen character.   “\n” indicates a newline character.   “\r” indicates a carriage return.   “\t” indicates a tab.   “\f” indicates a form feed.   “\d” indicates a digit (same as “[0-9]”).   “\D” indicates a non-digit.   “\w” indicates a word character (same as “[0-9a-z_A-Z]”).   “\W” indicates a non-word character.   “\s” indicates a whitespace character.   “\S” indicates a non-whitespace character.       

   Additional and/or different string definitions can also be used to define a regular expression search. In general, a regular expression search is a flexible search definition that allows for a search of a large number of potential strings. 
   In one embodiment, for each character, an existence list is maintained in root existence table  110 . The character is used as an index to one of 256 entries in root existence table  110 . In one embodiment, the entries of root existence table  110  includes an existence list pointer (ELP) that is used to indicate information related to an active root. One embodiment of a root existence table is described in greater detail below with respect to  FIG. 4 . 
   The ELP is returned to root node processor  100  for use in further processing. In one embodiment, an ELP value of zero indicates that the corresponding character is not a valid root. In one embodiment, the root node processor  100  passes the ELP to an active list processor (ALP)  160 . The active list processor  160  maintains a root active list (RAL)  120  and a state active list (SAL)  150 . The state active list  150  maintains a list of all the active nodes. The root active list  120  is a list maintained for handling root characters. In one embodiment, the entries of the root active list  120  include a node pointer (NP) that points to a node corresponding to the next character in the string of interest. One embodiment of a root active list is described in greater detail below with respect to  FIG. 5 . The ELP points to an entry in the root active list  120 . The active list processor  160  retrieves the entry pointed to by the ELP for further processing. 
   In one embodiment, the active list processor  160  passes the NP corresponding to the retrieved entry to an active node processor (ANP)  130  for further processing. In one embodiment, the active node processor  130  maintains a tree table structure  140 . Each entry in the tree table structure  140  corresponds to a character in the string of interest. One embodiment of a tree table structure is described in greater detail below in respect to  FIG. 6 . 
   The NP points to an entry in the tree table structure (TTS)  140 . The active node processor  130  retrieves the entry pointed to by the NP for further processing. In one embodiment, after an entry is fetched from the tree table structure  140 , the entry is compared to the current character in the data stream. If there is no match, the corresponding FSA may be aborted. If there is a match, the node is inserted into the state active list  150 . The active list processor  160  retrieves entries corresponding to the nodes in the state active list  150  when the next character in the data stream is fetched. When a string of characters  170  in a data stream match a string of interest being searched for, the match  180  may be reported by the active node processor  130 . 
     FIG. 2  illustrates an exemplary state diagram of one embodiment of a finite state automaton (FSA). In one embodiment, the strings (or patterns) searched for are specified as a collection of one or more regular expressions; however, other definitions can also be used. In the example illustrated in  FIG. 2 , the following strings are searched for:
         Get .* A   Get .* B
 
where “.” indicates any value except a new line and “*” indicates a general wildcard. Other expression indicators can also be used.
       
   In this example, the FSA begins at state S 0  at  202 . If a root character of a data stream matches the root character, “G”, of the FSA, then the FSA is activated. The FSA moves to state S 1  at  204 . The next character in the data stream is compared to the next character, “e”, of the string of interest. At any time there is no match, the FSA is aborted. If there is a match, the FSA moves to state S 2  at  206 . Then, the next character in the data stream is compared to the next character, “t”, of the string of interest. If there is a match, the FSA moves to state S 3  at  208 . Then, the next character in the data stream is compared to “.*”. If there is a match, the FSA moves to state S 4  at  210 . Since “.*” may consume more than one character, the FSA may stay at state S 4  until a character in the data stream does not match “.*” or matches one of the next characters in the strings of interest, “A” or “B”. If a character in the data stream matches “A”, then the FSA moves to state S 5  at  212 . S 5  is a terminal state, indicating that A is the last character in a string of interest, and characters in the data stream have matched the string “Get .*A”. If a character in the data stream matches “B”, then the FSA moves to state S 6  at  214 . S 6  is a terminal state, indicating that B is the last character in a string of interest, and characters in the data stream have matched the string “Get .*B”. Once a terminal state has been reached, the result of a match may be reported. In one embodiment, the active node processor  130  generates a report indicating any matched strings of interest. 
     FIG. 3  illustrates an embodiment of a node tree  300 . The root node  310  indicates the potential root characters of a string of interest. The root node  310  has one or more children. There are two types of children: primary and secondary. Primary children can consume only one character in a string, such as “[Gg]” or “[pqrt]”. Secondary children can consume zero or more characters in a string, such as “[ab]*” or “.*”. The root node  310  has one primary child, node  320 . Node  320  has one primary child, node  330 . Node  330  has one secondary child, node  340 . Node  340  has two primary children, nodes  350  and  360 . 
     FIG. 4  illustrates an embodiment of a root existence table  110 . In this embodiment, root existence table  110  contains three fields: the entry  400 , existence list pointer  410  (ELP), and existence count (EC)  420 . The entry  400  corresponds to a root character in a string of interest. The ELP  410  points to a corresponding entry in the root active list  120  that contains more information about the root node. The EC  420  indicates the number of children the root node has. Additional and/or different fields can also be included in root existence table  110 . 
     FIG. 5  illustrates an embodiment of a root active list  120 . Root active list  120  contains additional information about the root nodes. In this embodiment, root active list  120  contains six fields: the entry  500 , node pointer (NP)  510 , secondary child list pointer (SCLP)  520 , secondary child count (SCC)  530 , pre-qualifier (PQ)  540 , and repeat bit (R)  550 . The entry  500  indicates the number assigned to the root node. The NP  510  points to an entry in tree table structure  140  that corresponds to a primary child of the root node. The SCLP  520  points to an entry in the tree table structure  140  that corresponds to a secondary child of the root node. The SCC  530  indicates how many secondary children the root node has. The pre-qualifier  540  indicates any conditions before qualifying the node. The repeat bit  550  indicates if more than one character can be consumed by the root node. Additional and/or different fields can also be included in root active list  120 . 
     FIG. 6  illustrates an embodiment of a tree table structure  140 . In this embodiment, the tree table structure  140  contains seven fields: the entry  600 , child list pointer (CLP)  610 , child count (CC)  620 , secondary child list pointer (SCLP)  630 , secondary child count (SCC)  640 , valid bit (VA)  650 , unique bit (U)  660 , terminal bit (T)  670 , virtual bit (VI)  680 , and qualifier (Q)  690 . Additional and/or different fields can also be included in tree table structure  140 . The entry  600  indicates the number assigned to the node. The CLP  610  points to an entry in tree table structure  140  that corresponds to a primary child of the node. The CC  620  indicates how many primary children the node has. The SCLP  630  points to an entry in tree table structure  140  that corresponds to a secondary child of the node. The SCC  640  indicates how many secondary children the node has. 
   The valid bit  650  indicates whether the node is valid. The valid bit is used to support dynamic deletion of nodes in the tree. If a node is deleted, the node is no longer valid. The unique bit  660  indicates whether the node is unique. If a node is unique and qualifies, then other children of the parent do not have to be explored. The terminal bit  670  indicates whether the node is terminal. A node is terminal if the node is the end of a string or pattern of interest. The virtual bit  680  indicates that the node is a virtual node and does not consume a character. The qualifier  690  is a 256-bit vector that indicates which characters will qualify the node. If a character in the data stream qualifies a node, indicating a match between the character in the data stream and a corresponding character in a string of interest, the corresponding FSA will move to the next state, and the next child node will be retrieved from the table tree structure  140  and compared to the next character in the data stream. 
   An illustrative example of a string search will now be described. For purposes of illustration, assume that the followings strings or patterns are being searched for:
         [Gg] [Ee] [Tt].* A   [Gg] [Ee] [Tt].* B   [Dd] [Bb] [Cc].* XYZ   [Pp] [Oo] [Ss] [Tt].* A B C
 
where “.” indicates any value except a new line, “*” indicates a general wildcard, and “[Gg]” indicates both uppercase and lowercase “g”. Assume that the root existence table  110 , the root active list  120 , and the tree table structure  140  contain entries as shown in  FIGS. 4 ,  5 , and  6  respectively. In this example, a data stream containing a data string “GetXYAB” is to be examined to determine if there is a match with any of the strings being searched for.
       

   The root character “G” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “G” is a root character being searched for. Since there is at least one string with a root character of “G” being searched for, there is an entry in the root existence table  110  that corresponds to “G”. Therefore, the root existence table  110  returns the existence list pointer  410  to the root node processor  100 . The root node processor  100  passes the existence list pointer  410  to the active list processor  160 . The existence list pointer  410  points to an entry in the root active list  120  containing information about the root node that corresponds to the root character “G”. As shown in  FIG. 4 , the existence list pointer  410  for entry “G” points to entry  5  in the root active list  120 . Therefore, the active list processor  160  accesses the root active list  120  and retrieves entry  5 . As shown in  FIG. 5 , the node pointer  510  corresponding to entry  5  points to entry  7  in the tree table structure  140 . The active list processor  160  passes the node pointer  510  to the active node processor  130 . At this point, the processing of the root character “G” is done. 
   The next character “e” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “e” is a root character being searched for. Since none of the strings being searched for have a root character of “e”, the root existence table  110  returns a “0” to root node processor  100 , indicating that no entry corresponding to a root character of “e” exists in the table. Next, the active node processor  130  uses the node pointer  510  to determine which entry to look up in the tree table structure  140 . The node pointer  510  points to entry  7 . Therefore, the active node processor  130  retrieves entry  7  from the tree table structure  140 . The child list pointer  610  of entry  7  points to entry  13  in the tree table structure  140 , indicating that node  13  is a child of node  7 . Therefore, the active node processor  130  retrieves entry  13  from the tree table structure  140 . The character “e” is compared to the qualifier of entry  13 . There is a match, so node  13  is inserted into the state active list  150 . At this point, the processing of the character “e” is done. 
   The next character “t” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “t” is a root character being searched for. Since none of the strings being searched for have a root character of “t”, the root existence table  110  returns a “0” to root node processor  100 , indicating that no entry corresponding to a root character of “t” exists in the table. Next, the active list processor  160  retrieves the first entry from the state active list  150 , which corresponds to node  13 . The active list processor  160  passes this information to active node processor  130 . Active node processor  130  retrieves entry  13  from the tree table structure  140 . The child list pointer  610  of entry  13  points to entry  16  in the tree table structure  140 , indicating that node  16  is a child of node  13 . Therefore, the active node processor  130  retrieves entry  16  from the tree table structure  140 . The character “t” is compared to the qualifier of entry  16 . There is a match, so node  16  is inserted into the state active list  150 . At this point, the processing of the character “t” is done. 
   The next character “X” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “X” is a root character being searched for. Since none of the strings being searched for have a root character of “X”, the root existence table  110  returns a “0” to root node processor  100 , indicating that no entry corresponding to a root character of “X” exists in the table. Next, the active list processor  160  retrieves the first entry from the state active list  150 , which corresponds to node  16 . The active list processor  160  passes this information to active node processor  130 . Active node processor  130  retrieves entry  16  from the tree table structure  140 . The child list pointer  610  and child count  620  are 0, indicating that node  16  has no primary children. However, the secondary child count  640  is 1, indicating that node  16  has one secondary child. The secondary child list pointer  630  points to entry  27 , indicating that node  27  is a secondary child of node  16 . Therefore, the active node processor  130  retrieves entry  27  from the tree table structure  140 . The character “X” is compared to the qualifier of entry  27 . There is a match, so node  27  is inserted into the state active list  150  with the repeat bit set, indicating that node  27  may consume more than one character. The child count of entry  27  is two, indicating that node  27  has two children: nodes  35  and  36 . Therefore, the active node processor  130  retrieves entries  35  and  36  from the tree table structure  140 . The character “X” is compared to the qualifier of entry  35 . There is no match. The character “X” is compared to the qualifier of entry  36 . There is no match. At this point, the processing of the character “X” is done. 
   The next character “Y” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “Y” is a root character being searched for. Since none of the strings being searched for have a root character of “Y”, the root existence table  110  returns a “0” to root node processor  100 , indicating that no entry corresponding to a root character of “Y” exists in the table. Next, the active list processor  160  retrieves the first entry from the state active list  150 , which corresponds to node  27 . The active list processor  160  passes this information to active node processor  130 . Active node processor  130  retrieves entry  27  from the tree table structure  140 . The character “Y” is compared to the qualifier of entry  27 . There is a match, so node  27  is re-inserted into the state active list  150  with the repeat bit set, indicating that node  27  may consume more than one character. The child count of entry  27  is two, indicating that node  27  has two children: nodes  35  and  36 . Therefore, the active node processor  130  retrieves entries  35  and  36  from the tree table structure  140 . The character “Y” is compared to the qualifier of entry  35 . There is no match. The character “Y” is compared to the qualifier of entry  36 . There is no match. At this point, the processing of the character “Y” is done. 
   The next character “A” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “A” is a root character being searched for. Since none of the strings being searched for have a root character of “A”, the root existence table  110  returns a “0” to root node processor  100 , indicating that no entry corresponding to a root character of “A” exists in the table. Next, the active list processor  160  retrieves the first entry from the state active list  150 , which corresponds to node  27 . The active list processor  160  passes this information to active node processor  130 . Active node processor  130  retrieves entry  27  from the tree table structure  140 . The character “A” is compared to the qualifier of entry  27 . There is a match, so node  27  is re-inserted into the state active list  150  with the repeat bit set, indicating that node  27  may consume more than one character. The child count of entry  27  is two, indicating that node  27  has two children: nodes  35  and  36 . Therefore, the active node processor  130  retrieves entries  35  and  36  from the tree table structure  140 . The character “A” is compared to the qualifier of entry  35 . There is a match. Since the terminal bit of entry  35  is 1, indicating that one of the strings to be searched for terminates with character “A”, a string to be searched for has been found, and this result may be reported. Since the unique bit of entry  35  is 1, indicating that the node is unique, no other children of entry  27  need to be explored. Therefore, the processing of the character “A” is done. 
   The next character “B” is retrieved from the data string “GetXYAB”. The root node processor  100  checks the root existence table  110  to determine whether “B” is a root character being searched for. Since none of the strings being searched for have a root character of “B”, the root existence table  110  returns a “0” to root node processor  100 , indicating that no entry corresponding to a root character of “B” exists in the table. Next, the active list processor  160  retrieves the first entry from the state active list  150 , which corresponds to node  27 . The active list processor  160  passes this information to active node processor  130 . Active node processor  130  retrieves entry  27  from the tree table structure  140 . The character “B” is compared to the qualifier of entry  27 . There is a match, so node  27  is re-inserted into the state active list  150  with the repeat bit set, indicating that node  27  may consume more than one character. The child count of entry  27  is two, indicating that node  27  has two children: nodes  35  and  36 . Therefore, the active node processor  130  retrieves entries  35  and  36  from the tree table structure  140 . The character “B” is compared to the qualifier of entry  35 . There is no match. The character “B” is compared to the qualifier of entry  36 . There is a match. Since the terminal bit of entry  36  is 1, indicating that one of the strings to be searched for terminates with character “B”, a string to be searched for has been found, and this result may be reported. Since the unique bit of entry  36  is 1, indicating that the node is unique, no other children of entry  27  need to be explored. Therefore, the processing of the character “B” is done. The end result is that the data stream containing “GetXYAB” matches two of the strings being searched for: “Get.*A” and “Get.*B”. The result of these matches may be reported by one of the processors. 
   In one embodiment, portions of the regular expression search can be implemented as sequences of instructions executed by an electronic system. The sequences of instructions can be stored by the electronic device or the instructions can be received by the electronic device (e.g., via a network connection).  FIG. 7  illustrates an embodiment of an electronic system. The electronic system illustrated in  FIG. 7  is intended to represent a range of electronic systems, for example, computer systems, network access devices, etc. Alternative electronic systems can include more, fewer and/or different components. 
   Electronic system  700  includes bus  701  or other communication device to communicate information, and processor  702  coupled to bus  701  to process information. While electronic system  700  is illustrated with a single processor, electronic system  700  can include multiple processors and/or co-processors. Electronic system  700  further includes random access memory (RAM) or other dynamic storage device  704  (referred to as memory), coupled to bus  701  to store information and instructions to be executed by processor  702 . Memory  704  also can be used to store temporary variables or other intermediate information during execution of instructions by processor  702 . 
   Electronic system  700  also includes read only memory (ROM) and/or other static storage device  706  coupled to bus  701  to store static information and instructions for processor  702 . Data storage device  707  is coupled to bus  701  to store information and instructions. Data storage device  707  such as a magnetic disk or optical disc and corresponding drive can be coupled to electronic system  700 . 
   Electronic system  700  can also be coupled via bus  701  to display device  721 , such as a cathode ray tube (CRT) or liquid crystal display (LCD), to display information to a computer user. Alphanumeric input device  722 , including alphanumeric and other keys, is typically coupled to bus  701  to communicate information and command selections to processor  702 . Another type of user input device is cursor control  723 , such as a mouse, a trackball, or cursor direction keys to communicate direction information and command selections to processor  702  and to control cursor movement on display  721 . Electronic system  700  further includes network interface  730  to provide access to a network, such as a local area network. 
   Instructions are provided to memory from a storage device, such as magnetic disk, a read-only memory (ROM) integrated circuit, CD-ROM, DVD, via a remote connection (e.g., over a network via network interface  730 ) that is either wired or wireless providing access to one or more electronically-accessible media, etc. In alternative embodiments, hard-wired circuitry can be used in place of or in combination with software instructions. Thus, execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. 
   An electronically-accessible medium includes any mechanism that provides (i.e., stores and/or transmits) content (e.g., computer executable instructions) in a form readable by an electronic device (e.g., a computer, a personal digital assistant, a cellular telephone). For example, a machine-accessible medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals); etc. 
   In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.