Copyright 2006, Palmsource, Inc., an ACCESS company. Sunnyvale, California, USA

Libsqlfs is free/open source software distributed under the GNU Lesser General Public License, version 2 or later versions as published by the Free Software Foundation. See the file COPYING for the complete licensing terms.

Libsqlfs can be downloaded from and Development sources are available via an GNU Arch archive; see below.


The libsqlfs library implements a POSIX style file system on top of an SQLite database. It allows applications to have access to a full read/write file system in a single file, complete with its own file hierarchy and name space. This is useful for applications which needs structured storage, such as embedding documents within documents, or management of configuration data or preferences. Libsqlfs can be used as an shared library, or it can be built as a FUSE (Linux File System in User Space) module to allow a libsqlfs database to be accessed via OS level file system interfaces by normal applications.


PalmSource software developers recently created libsqlfs. This library is an adjunct to the very popular open source SQLite database software. Libsqlfs was created as part of PalmSource's ALP mobile phone platform, but it is useful in many other applications too.

The libsqlfs library provides an easy way for applications to put an entire read/write file system into a relational database as a single file in the host file system. Such a file system can easily be moved around, backed up or restored as a single file. But the file system can also be accessed as individual files. This provides great flexibility and convenience.

We concluded that a simpler way to meet our needs was to write a library that supported the POSIX file system semantics on an SQL database. This brings the benefits of a real database, such as transactions and concurrency control, and allows us to have complete control over the schema of the preferences, so we can allow additional metadata such as value types, permissions and access control lists. Our libsqlfs registry can accommodate small preference values such as a number, and large binary objects such as an video clip. The library provides a generic file system layer that maps a file system onto a SQLite database, and supports a POSIX file system semantics.

To speed development, we built our file system mapping layer as a File System In User Space (FUSE) module. FUSE is another open source project. It is a kernel module that supports user-level implementations of file systems. Our design allows libsqlfs to implement a real file system at the OS level, and apply real file system operations on it. We tested the complete build process of gcc and the Linux kernel on top of libsqlfs, and we successfully executed fsx.c, the Apple file system test tool, against libsqlfs.

Today the ALP Global Settings component uses libsqlfs as the storage back-end. Libsqlfs provides an easy way for applications to support a read/write file system totally contained in a relational database as a single file in the host file system, without using SQL statements. Libsqlfs provides a superset of the storage features of GConf, and can be used as the storage back end of other desktop preference services. Libsqlfs is also useful wherever developers need to organize data, and sometimes treat it as one file, and at other times treat it as a collection of individually writable files.


As a Library

Libsqlfs provides a GNU autoconf/automake based build system for building as an application library. To build, please follow the normal GNU configure conventions. Normally, the following command is all what's needed:
./configure --prefix=install dir
make && make install
install dir defaults to /usr/local if not specified.

You have to be root for installing into system directories such as /usr/local.

Both a static library and a shared library are built, unless you specify otherwise via options to configure.

As an FUSE module

Currently FUSE module build is not integrated with the configure script; instead a script compile_fuse is supplied for building the module. You may need to edit the include paths to adjust for your particular environment.

After running the script you shall have an executable called fuse_libsqlfs. Run it as root to start a FUSE session on top of libsqlfs:

then you shall see the libsqlfs file space exposed, and can be accessed by normal applications, via the .


fuse_libsqlfs /mnt/sqlfs &

ls /mnt/sqlfs
The location of the SQLite database is hard-coded in fuse_main.c. Change the argument to sqlfs_init() to suit your needs.


A libsqlfs session is represented by an object of type sqlfs_t. All APIs require an explicit reference to a valid sqlfs_t.

Each file is a "key" in the internal libsqlfs vocabulary. File metadata are represented as objects of the sturct key_attr. File contents are represented by the struct key_value.

File metadata are the normal POSIX file attributes as expected except an additional "type" which can not be visible via the normal file attribute functions. The "type" is used to support the specific needs of the setting registry application and can be one of the following:

Integer (32-bit)
Double (a C double)
String (a C zero-terminated string)
Sym_link (symbolic link)
Bool  (a boolean)
List (a Glib list of values)
Blob (a binary object)
Note all other file system primitives do not make use of the "type"; to them all files are blobs. At this point the "type" is meant for use by higher up application logic in applications using libsqlfs.

Libsqlfs started as an FUSE module so it implements the primitives as defined by FUSE version 2.5.3. Specifically, the following file system primitives are implemented:

int sqlfs_proc_getattr(sqlfs_t *, const char *path, struct stat *stbuf);
int sqlfs_proc_access(sqlfs_t *, const char *path, int mask);
int sqlfs_proc_readlink(sqlfs_t *, const char *path, char *buf, size_t size);
int sqlfs_proc_readdir(sqlfs_t *, const char *path, void *buf, fuse_fill_dir_t filler, 
                  off_t offset, struct fuse_file_info *fi);
int sqlfs_proc_mknod(sqlfs_t *, const char *path, mode_t mode, dev_t rdev);
int sqlfs_proc_mkdir(sqlfs_t *, const char *path, mode_t mode);
int sqlfs_proc_unlink(sqlfs_t *, const char *path);
int sqlfs_proc_rmdir(sqlfs_t *, const char *path);
int sqlfs_proc_symlink(sqlfs_t *, const char *path, const char *to);
int sqlfs_proc_rename(sqlfs_t *, const char *from, const char *to);
int sqlfs_proc_link(sqlfs_t *, const char *from, const char *to);
int sqlfs_proc_chmod(sqlfs_t *, const char *path, mode_t mode);
int sqlfs_proc_chown(sqlfs_t *, const char *path, uid_t uid, gid_t gid);
int sqlfs_proc_truncate(sqlfs_t *, const char *path, off_t size);
int sqlfs_proc_utime(sqlfs_t *, const char *path, struct utimbuf *buf);
int sqlfs_proc_open(sqlfs_t *, const char *path, struct fuse_file_info *fi);
int sqlfs_proc_read(sqlfs_t *, const char *path, char *buf, size_t size, off_t offset, struct
    fuse_file_info *fi);
int sqlfs_proc_write(sqlfs_t *, const char *path, const char *buf, size_t size, off_t offset,
    struct fuse_file_info *fi);
int sqlfs_proc_statfs(sqlfs_t *, const char *path, struct statvfs *stbuf);
int sqlfs_proc_release(sqlfs_t *, const char *path, struct fuse_file_info *fi);
int sqlfs_proc_fsync(sqlfs_t *, const char *path, int isfdatasync, struct fuse_file_info *fi);

Their semantics are as defined by the FUSE documentation and the corresponding Unix file system calls. Following the FUSE conventions, all file or key paths must be absolute and start with a '/'. Applications can provide their own logic for relative paths before passing the "normalized" absolute paths to these FUSE primitive routines.

Extended attributes are not yet supported in this version.

In addition, other APIs provide environment setup, support for transaction and convenience functions:

int sqlfs_init(const char *)
    initialize the libsqlfs library and sets the default database file name.

int sqlfs_open(const char *db, sqlfs_t **);
    creates a new connection to the libsqlfs database.  The first argument,
    if not NULL,specifies a different database file from the default.

int sqlfs_close(sqlfs_t *);
    closes and frees a libsqlfs connection.

int sqlfs_del_tree(sqlfs_t *sqlfs, const char *key);
    deletes a whole subtree.

int sqlfs_get_value(sqlfs_t *sqlfs, const char *key, key_value *value, 
    size_t begin, size_t end); 
    reads contents of a file contained in a range
    (between offsets begin and end)

int sqlfs_set_value(sqlfs_t *sqlfs, const char *key, const key_value *value, 
    size_t begin,  size_t end);
    writes contents of a file contained in a range
    (between offsets begin and end)

int sqlfs_get_attr(sqlfs_t *sqlfs, const char *key, key_attr *attr);
    reads the metadata of a file
int sqlfs_set_attr(sqlfs_t *sqlfs, const char *key, const key_attr *attr);
    write the metadata of a file

int sqlfs_set_type(sqlfs_t *sqlfs, const char *key, const char *type);
    sets the "type" of the file content. 
int sqlfs_begin_transaction(sqlfs_t *sqlfs);
    begins a SQLite transaction
int sqlfs_complete_transaction(sqlfs_t *sqlfs, int i);
    ends a SQLite transaction
Note the transaction supports "levels"; that is, transaction calls can be nested and libsqlfs maintains an internal level count of the current transaction level. The actual SQLite transaction are only started when the level goes above 0 and only ended when the level falls to zero.

For a sample application showing the usage of libsqlfs, see the test program test.c in the test directory.

Supported Platforms

To date, libsqlfs is tested on 32-bit i386 GNU/Linux (Ubnutu 5.04) and StrongArm (Treo 650 phone) Access Linux Platform.

Currently libsqlfs, when used as a library, only has been tested on GNU/Linux (Ubnutu and Red Hat Fedora 5) although it shall be usable on any Unix like platforms where SQLite runs with at most minor changes. It shall also work on the Cygwin enviroment but this is not tested. Patches for different platform support are welcome.

For use at the OS level, libsqlfs only supports the FUSE on the Linux kernel on both 32-bit i386 and StrongArm.

Supported Database

To date, only SQLite is supported.

Mailing List

A general discussion list for libsqlfs is available: . To subscribe, go to

Source Repository: Arch

Latest development source code of libsqlfs is available via the GNU Arch archive at

in the branch


Older sources are also available via CVS. See for more information on how to access the CVS repository.

For further inquiries, please contact:

Peter van der Linden,
Andy Tai,