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 http://download.savannah.nongnu.org/releases/libsqlfs/ and http://www.palmsource.com/opensource/downloads.html. Development sources are available via an GNU Arch archive; see below.
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.
./configure --prefix=install dir make && make installinstall 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.
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:
fuse_libsqlfsthen you shall see the libsqlfs file space exposed, and can be accessed by normal applications, via the
example:
fuse_libsqlfs /mnt/sqlfs & ls /mnt/sqlfsThe location of the SQLite database is hard-coded in fuse_main.c. Change the argument to sqlfs_init() to suit your needs.
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:
Null Dir 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.
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.
atai@gnu.org--libsqlfs
http://arch.gnu.org/archives/libsqlfs/atai@gnu.org--libsqlfs/
in the branch
libsqlfs--main--1.0
For further inquiries, please contact:
Peter van der Linden, peter.vanderlinden@palmsource.com
Andy Tai, andy.tai@palmsource.com