@@ -1,9 +1,10 @@ #include "bdb_drv.h" +// Callback Array static ErlDrvEntry basic_driver_entry = { NULL, /* init */ - start, /* startup */ - stop, /* shutdown */ + start, /* startup (defined below) */ + stop, /* shutdown (defined below) */ NULL, /* output */ NULL, /* ready_input */ NULL, /* ready_output */ @@ -12,7 +13,7 @@ static ErlDrvEntry basic_driver_entry = { NULL, /* handle */ NULL, /* control */ NULL, /* timeout */ - outputv, /* outputv */ + outputv, /* outputv (defined below) */ NULL, /* ready_async */ NULL, /* flush */ NULL, /* call */ @@ -27,16 +28,19 @@ DRIVER_INIT(basic_driver) { return &basic_driver_entry; } +// Driver Start static ErlDrvData start(ErlDrvPort port, char* cmd) { bdb_drv_t* retval = (bdb_drv_t*) driver_alloc(sizeof(bdb_drv_t)); u_int32_t open_flags = DB_CREATE | DB_THREAD; DB *db; int status; + // Create and open the database db_create(&db, NULL, 0); status = db->open(db, NULL, DB_PATH, NULL, DB_BTREE, open_flags, 0); if(status != 0) { + // There was an error opening the database char *error_reason; switch(status){ @@ -58,12 +62,15 @@ static ErlDrvData start(ErlDrvPort port, char* cmd) { fprintf(stderr, "Unabled to open file: %s because %s\n\n", DB_PATH, error_reason); } + // Set the state for the driver retval->port = port; retval->db = db; return (ErlDrvData) retval; } + +// Driver Stop static void stop(ErlDrvData handle) { bdb_drv_t* driver_data = (bdb_drv_t*) handle; @@ -71,10 +78,11 @@ static void stop(ErlDrvData handle) { driver_free(driver_data); } +// Handle input from Erlang VM static void outputv(ErlDrvData handle, ErlIOVec *ev) { bdb_drv_t* driver_data = (bdb_drv_t*) handle; ErlDrvBinary* data = ev->binv[1]; - int command = data->orig_bytes[0]; + int command = data->orig_bytes[0]; // First byte is the command switch(command) { case CMD_PUT: @@ -94,6 +102,7 @@ static void outputv(ErlDrvData handle, ErlIOVec *ev) { } } +// Insert or replace record in the database static void put(bdb_drv_t *bdb_drv, ErlIOVec *ev) { ErlDrvBinary* input = ev->binv[1]; char *bytes = input->orig_bytes; @@ -106,6 +115,7 @@ static void put(bdb_drv_t *bdb_drv, ErlIOVec *ev) { DBT value; int status; + // Erase bytes to get rid of residual data bzero(&key, sizeof(DBT)); bzero(&value, sizeof(DBT)); @@ -115,14 +125,19 @@ static void put(bdb_drv_t *bdb_drv, ErlIOVec *ev) { value.data = value_bytes; value.size = value_size; + // Insert the record and then write it to disk status = db->put(db, NULL, &key, &value, 0); db->sync(db, 0); if(status == 0) { + // Insert went OK + // Prepare return value to Erlang VM, returns atom 'ok' ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("ok")}; + // Return the value to the Erlang VM driver_output_term(bdb_drv->port, spec, sizeof(spec) / sizeof(spec[0])); } else { + // There was an error return {error, Reason} char * error_reason; switch(status) { @@ -145,6 +160,7 @@ static void put(bdb_drv_t *bdb_drv, ErlIOVec *ev) { error_reason = "unkown"; } + // Returns tuple {error, Reason} ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("error"), ERL_DRV_ATOM, driver_mk_atom(error_reason), ERL_DRV_TUPLE, 2}; @@ -153,6 +169,7 @@ static void put(bdb_drv_t *bdb_drv, ErlIOVec *ev) { } } +// Retrieve a record from the database, if it exists static void get(bdb_drv_t *bdb_drv, ErlIOVec *ev) { ErlDrvBinary* input = ev->binv[1]; ErlDrvBinary *output_bytes; @@ -170,18 +187,25 @@ static void get(bdb_drv_t *bdb_drv, ErlIOVec *ev) { key.data = key_bytes; key.size = KEY_SIZE; - value.flags = DB_DBT_MALLOC; // Don't forget to free + // Have BerkeleyDB allocate memory big enough to store the value + value.flags = DB_DBT_MALLOC; // Don't forget to free it later + // Retrieve the record status = db->get(db, NULL, &key, &value, 0); if(status == 0) { + // Get went OK + + // Copy the record value to an output structure to return to Erlang VM output_bytes = driver_alloc_binary(value.size); output_bytes->orig_size = value.size; - // TODO:Figure out if we can somehow use this original memory - //binary->orig_bytes = (char *)&data.data; memcpy(output_bytes->orig_bytes, value.data, value.size); free(value.data); + // TODO:Figure out if we can somehow use this original memory without recopying a la: + //binary->orig_bytes = (char *)&data.data; + + // Returns tuple {ok, Data} ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("ok"), ERL_DRV_BINARY, (ErlDrvTermData) output_bytes, output_bytes->orig_size, 0, ERL_DRV_TUPLE, 2}; @@ -189,6 +213,7 @@ static void get(bdb_drv_t *bdb_drv, ErlIOVec *ev) { driver_output_term(bdb_drv->port, spec, sizeof(spec) / sizeof(spec[0])); driver_free_binary(output_bytes); } else { + // there was an error char *error_reason; switch(status) { @@ -211,6 +236,7 @@ static void get(bdb_drv_t *bdb_drv, ErlIOVec *ev) { error_reason = "unknown"; } + // Return tuple {error, Reason} ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("error"), ERL_DRV_ATOM, driver_mk_atom(error_reason), ERL_DRV_TUPLE, 2}; @@ -218,6 +244,7 @@ static void get(bdb_drv_t *bdb_drv, ErlIOVec *ev) { } } +// Delete a record from the database static void del(bdb_drv_t *bdb_drv, ErlIOVec *ev) { ErlDrvBinary* data = ev->binv[1]; char *bytes = data->orig_bytes; @@ -236,11 +263,13 @@ static void del(bdb_drv_t *bdb_drv, ErlIOVec *ev) { db->sync(db, 0); if(status == 0) { + // Delete went OK, return atom 'ok' ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("ok")}; driver_output_term(bdb_drv->port, spec, sizeof(spec) / sizeof(spec[0])); } else { + // There was an error char *error_reason; switch(status) { @@ -266,6 +295,7 @@ static void del(bdb_drv_t *bdb_drv, ErlIOVec *ev) { error_reason = "unknown"; } + // Return tuple {error, Reason} ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("error"), ERL_DRV_ATOM, driver_mk_atom(error_reason), ERL_DRV_TUPLE, 2}; @@ -274,7 +304,9 @@ static void del(bdb_drv_t *bdb_drv, ErlIOVec *ev) { } } +// Unkown Command static void unkown(bdb_drv_t *bdb_drv, ErlIOVec *ev) { + // Return {error, unkown_command} ErlDrvTermData spec[] = {ERL_DRV_ATOM, driver_mk_atom("error"), ERL_DRV_ATOM, driver_mk_atom("uknown_command"), ERL_DRV_TUPLE, 2}; priv/bdb_drv.c @@ -4,14 +4,20 @@ #include <string.h> #include <db.h> +// Path to file where data will be stored. +// It will be created if it doesn't exist #define DB_PATH "./store.db" +// Binary commands between Erlang VM and Driver #define CMD_PUT 1 #define CMD_GET 2 #define CMD_DEL 3 +// Number of bytes for each key +// (160 bits for SHA1 hash) #define KEY_SIZE 20 +// Define struct to hold state across calls typedef struct _bdb_drv_t { ErlDrvPort port; priv/bdb_drv.h f6c097bf646e5bd3269c12a4c7146f14fea90bba Matt Williamson dawsdesign@gmail.com http://github.com/dawsdesign/erl_bdb_sample/commit/8d8c19b376b3ca89bc28c4037bcd6234b930edd1 8d8c19b376b3ca89bc28c4037bcd6234b930edd1 2009-05-26T09:02:52-07:00 2009-05-26T09:02:52-07:00 Added comments to C sources c91a8ab777716a97f33d1d9256b2522562405e84 Matt Williamson dawsdesign@gmail.com