fdb - filesystem database

fdb provides a simple model for creating databases, as well as an thread safe and POSIX compliant interface implementing such model, all using an underlying tree-structured file system.

fdb database model

fdb structures data in a tree (just as the tree-structured filesystem) based on the following main concepts:

• root: bank not in a bank (the root of the tree).
• bank: collection of banks identified by a string and the bank or root it is in (middle node in the tree).
• registry: chunk of data identified by a string and the bank they are in (leaf node in the tree).

As it is apparent, in the file system banks are represented by directories and registries by files. Therefore, the underlying filesystem must have both to be able to support a database following this model.

fdb library

The fdb interface is defined in the file fdb.h. It provides functions to manage banks and registries as expected, which are all described in the file.

To access and modify the data in registries, the implementation maps them to memory to allow easy, thread-safe cache implementations, delegating cache management and policies to the operating system.

The path of the root bank is /var/fdb by default, but can be specified through an environment variable. By default, fdb will use the variable FDB_ROOT, but this can be changed passing a non-null string to fdb_init with the name of the environment variable where to read the path of the root from.

Usage example

fsh_bank bank, fdb_reg reg;

char *bank_name = "bank_name";
char *reg_name  = "reg_name";

struct data reg_data;

fdb_init("EXAMPLE_ROOT"); // read root path from $EXAMPLE_ROOT

// create bank in the root bank
if (fdb_bank_create (FDB_ROOT, bank_name, &bank) != -1) {
    if (fdb_bank_getreg (bank, reg_name, &reg) == 0) {
        // if the regisry exists, read its data
        fdb_reg_open (&reg, sizeof (reg_data));
        fdb_reg_read (&reg, &reg_data);
        fdb_reg_close (&reg);
        fdb_reg_destroy (&reg);
    } else if (fdb_reg_create (bank, reg_name, &reg) == 0) {
        // if the registry does not exist, create it and write the data
        fdb_reg_open (&reg, sizeof (reg_data));
        fdb_reg_write (&reg, &reg_data);
        fdb_reg_close (&reg);
        fdb_reg_destroy (&reg);
    } else {
        // something failed opening or creating the registry
        perror(reg_name);
    }
} else {
    // something failed
    perror("bank_create");
}

Building fdb

Use the all target of the makefile to generate the library libfdb.a. Use the install target to copy the library and headers in /usr.

$> make all
$> sudo make install