The lightweight storage library

struct osl_object

• void *data: Pointer to the data of the object.
• size_t size: The object's size.

enum osl_table_flags

• OSL_LARGE_TABLE = 1: This table will have many rows.

enum osl_storage_type

• OSL_MAPPED_STORAGE: All data for this column is stored in one file which gets mmapped by osl_open_table(). This is suitable for columns that do not hold much data.
• OSL_DISK_STORAGE: Each entry is stored on disk and is loaded on demand by open_disk_object(). This is the preferable storage type for large objects that need not be in memory all the time.
• OSL_NO_STORAGE: Objects for columns of this type are volatile: They are only stored in memory and are discarded when the table is closed.

enum osl_storage_flags

• OSL_RBTREE = 1: Build an rbtree for this column. This is only possible if the storage type of the column is either OSL_MAPPED_STORAGE or OSL_NO_STORAGE. In order to lookup objects in the table by using osl_get_row(), the lookup column must have an associated rbtree.

  See also: osl_storage_type, osl_get_row()

• OSL_FIXED_SIZE = 2: The data for this column will have constant size.
• OSL_UNIQUE = 4: All values are different. Must be set if OSL_RBTREE is set.
• OSL_DONT_FREE = 8: Do not free the data for this column (OSL_NO_STORAGE).

struct osl_table

struct osl_row

typedef int osl_compare_func(const struct osl_object *obj1, const struct osl_object *obj2)

To build an rbtree, a compare function for the objects must be provided. This function takes pointers to the two objects to be compared. It must return -1, zero, or 1, if the first argument is considered to be respectively less than, equal to, or greater than the second. If two members compare as equal, their order in the rbtree is undefined.

typedef int osl_rbtree_loop_func(struct osl_row *row, void *data)

The osl_rbreee_loop functions take a function pointer of this type. For each node in the rbtree, the given function is called.

See also: osl_rbtree_loop(), osl_rbtree_loop_reverse().

struct osl_column_description

• uint16_t storage_type: One of the three possible types of storage. See also: osl_storage_type.
• uint16_t storage_flags: Specifies further properties of the column. See also: osl_storage_flags.
• char *name: The column name determines the name of the directory where all data for this column will be stored. Its hash is stored in the table header. This field is ignored if the storage type is NO_STORAGE.
• osl_compare_func *compare_function: For columns with an associated rbtree, this must point to a function that compares the values of two objects, either a built-in function or a function defined by the application may be supplied. This field is ignored if the column does not have an associated rbtree.

  See also: osl_storage_flags, osl_compare_func

• uint32_t data_size: If the OSL_FIXED_SIZE flag is set for this column, this value describes the number of bytes of each object of this column. It is ignored, if OSL_FIXED_SIZE is not set.

struct osl_table_description

A pointer to the table description is passed to osl_create_table() and osl_open_table(). The osl library calls which operate on an open table refer to the fields of the table description through this pointer. Hence the table description must not be modified or freed before the table is closed.

• const char *dir: The directory which contains all files of this table. This may be either relative to the cwd or an absolute path.
• const char *name: The table name. A subdirectory of dir called name is created at table creation time. It must be a valid name for a subdirectory. In particular, no slashes are allowed in the name.
• uint16_t num_columns: The number of columns of this table.
• uint8_t flags: Further table-wide information, see osl_table_flags.
• struct osl_column_description *column_descriptions: The array describing the individual columns of the table.

enum osl_close_flags

• OSL_MARK_CLEAN = 1: The table header contains a "dirty" flag which indicates whether the table is currently held open by another process. The OSL_MARK_CLEAN flag instructs libosl to clear the dirty flag when the table is closed.
• OSL_FREE_VOLATILE = 2: If the table contains columns of type OSL_NO_STORAGE and this flag is passed to osl_close_table(), free(3) is called for each object of each column of type OSL_NO_STORAGE.

int osl_create_table(const struct osl_table_description *desc)

• const struct osl_table_description *desc: Pointer to the table description

• Standard

int osl_open_table(const struct osl_table_description *desc, struct osl_table **result)

An osl table must be opened before its data can be accessed.

• const struct osl_table_description *desc: Describes the table to be opened
• struct osl_table **result: Contains a pointer to the open table on success.

The table description given by desc should coincide with the description used at creation time.

• Standard

int osl_close_table(struct osl_table *t, enum osl_close_flags flags)

• struct osl_table *t: Pointer to the table to be closed.
• enum osl_close_flags flags: Options for what should be cleaned up.

If osl_open_table() succeeds, the resulting table pointer must later be passed to this function in order to flush all changes to the file system and to free the resources that were allocated by osl_open_table().

• Standard

int osl_get_row(const struct osl_table *t, unsigned col_num, const struct osl_object *obj, struct osl_row **result)

• const struct osl_table *t: Pointer to an open osl table
• unsigned col_num: The number of the column to be searched
• const struct osl_object *obj: The object to be looked up
• struct osl_row **result: Points to the row containing the given object

Lookup the given object and return the row containing it. The column specified by col_num must have an associated rbtree.

• Standard. The result pointer is set to NULL if and only if the function returns negative.

int osl_get_object(const struct osl_table *t, const struct osl_row *row, unsigned col_num, struct osl_object *object)

• const struct osl_table *t: Pointer to an open osl table
• const struct osl_row *row: Pointer to the row
• unsigned col_num: The column number
• struct osl_object *object: The result pointer

The column determined by col_num must be of type OSL_MAPPED_STORAGE or OSL_NO_STORAGE, i.e. no disk storage objects may be retrieved by this function.

See also: osl_storage_type, osl_open_disk_object().

• Standard

int osl_open_disk_object(const struct osl_table *t, const struct osl_row *r, unsigned col_num, struct osl_object *obj)

For columns of type OSL_DISK_STORAGE this function must be used to retrieve one of its containing objects. Afterwards, osl_close_disk_object() must be called in order to deallocate the resources.

• const struct osl_table *t: Pointer to an open osl table
• const struct osl_row *r: Pointer to the row containing the object
• unsigned col_num: The column number
• struct osl_object *obj: Points to the result upon successful return

See also: osl_get_object(), osl_storage_type, osl_close_disk_object().

• Standard

int osl_close_disk_object(struct osl_object *obj)

• struct osl_object *obj: Pointer to the object previously returned by open_disk_object()

• The return value of the underlying call to munmap(2)

int osl_add_and_get_row(struct osl_table *t, struct osl_object *objects, struct osl_row **row)

• struct osl_table *t: Pointer to an open osl table
• struct osl_object *objects: Array of objects to be added
• struct osl_row **row: Result pointer

The objects parameter must point to an array containing one object per column. The order of the objects in the array is given by the table description of the table. Several sanity checks are performed during object insertion and the function returns without modifying the table if any of these tests fail. In fact, it is atomic in the sense that it either succeeds or leaves the table unchanged (i.e. either all or none of the objects are added to the table).

See also: struct osl_table_description, osl_compare_func, osl_add_row().

• Standard

int osl_add_row(struct osl_table *t, struct osl_object *objects)

• struct osl_table *t: Same meaning as osl_add_and_get_row()
• struct osl_object *objects: Same meaning as osl_add_and_get_row()

This is equivalent to calling osl_add_and_get_row(t, objects, NULL);

• The return value of the underlying call to osl_add_and_get_row()

int osl_del_row(struct osl_table *t, struct osl_row *row)

• struct osl_table *t: Pointer to an open osl table
• struct osl_row *row: Pointer to the row to delete

This removes all disk storage objects, removes all rbtree nodes, and frees all volatile objects belonging to the given row. For mapped columns, the data is merely marked invalid and may be pruned from time to time by oslfsck(1).

• Standard

int osl_rbtree_loop(const struct osl_table *t, unsigned col_num, void *private_data, osl_rbtree_loop_func *func)

• const struct osl_table *t: Pointer to an open osl table
• unsigned col_num: The column to use for iterating over the elements
• void *private_data: Pointer that gets passed to the callback function
• osl_rbtree_loop_func *func: This callback is called for each node in the rbtree.

This function does an in-order walk of the rbtree associated with col_num. It is an error if the OSL_RBTREE flag is not set for this column. For each node in the rbtree, the given function func is called with two pointers as arguments: The first osl_row* argument points to the row that contains the object corresponding to the rbtree node currently traversed, and the private_data pointer is passed verbatim as the second argument. The loop terminates either if the callback returns a negative value, or if all nodes of the tree have been visited.

• Standard. If the termination of the loop was caused by the callback returning a negative value, -E_OSL_LOOP is returned. This is the only possible error.

int osl_rbtree_loop_reverse(const struct osl_table *t, unsigned col_num, void *private_data, osl_rbtree_loop_func *func)

This function is identical to osl_rbtree_loop(), the only difference is that the tree is walked in reverse order.

• const struct osl_table *t: See osl_rbtree_loop()
• unsigned col_num: See osl_rbtree_loop()
• void *private_data: See osl_rbtree_loop()
• osl_rbtree_loop_func *func: See osl_rbtree_loop()

See also: osl_rbtree_loop().

• The same return value as osl_rbtree_loop()

int osl_update_object(struct osl_table *t, const struct osl_row *r, unsigned col_num, struct osl_object *obj)

• struct osl_table *t: Pointer to an open osl table
• const struct osl_row *r: Pointer to the row containing the object to be updated
• unsigned col_num: Number of the column containing the object to be updated
• struct osl_object *obj: Pointer to the replacement object

This function gets rid of all references to the old object. This includes removal of the rbtree node in case there is an rbtree associated with col_num. It then inserts obj into the table and the rbtree if necessary.

• Standard

int osl_get_num_rows(const struct osl_table *t, unsigned *num_rows)

• const struct osl_table *t: Pointer to an open osl table
• unsigned *num_rows: Result is returned here

The number of rows returned excludes any invalid rows.

• Positive on success, -E_OSL_BAD_TABLE if t is NULL

int osl_rbtree_first_row(const struct osl_table *t, unsigned col_num, struct osl_row **result)

• const struct osl_table *t: An open table
• unsigned col_num: The number of the rbtree column
• struct osl_row **result: A pointer to the first row is returned here

The rbtree node of the smallest object (with respect to the corresponding compare function) is selected and the row containing this object is returned. It is an error if col_num refers to a column without an associated rbtree.

See also: osl_get_nth_row(), osl_rbtree_last_row().

• Standard

int osl_rbtree_last_row(const struct osl_table *t, unsigned col_num, struct osl_row **result)

This function works just like osl_rbtree_first_row(), the only difference is that the row containing the greatest rather than the smallest object is returned.

• const struct osl_table *t: See osl_rbtree_first_row()
• unsigned col_num: See osl_rbtree_first_row()
• struct osl_row **result: See osl_rbtree_first_row()

See also: osl_get_nth_row(), osl_rbtree_first_row()

• Standard

int osl_get_nth_row(const struct osl_table *t, unsigned col_num, unsigned n, struct osl_row **result)

• const struct osl_table *t: Pointer to an open osl table
• unsigned col_num: The column number
• unsigned n: The rank of the desired row
• struct osl_row **result: Row is returned here

Retrieve the n-th order statistic with respect to the compare function of the rbtree column col_num. In other words, get the row with n-th greatest value in column col_num. It is an error if col_num is not a rbtree column, or if n is larger than the number of rows in the table.

• Standard

int osl_get_rank(const struct osl_table *t, struct osl_row *r, unsigned col_num, unsigned *rank)

The rank is, by definition, the position of the row in the linear order determined by an in-order tree walk of the rbtree associated with given column number.

• const struct osl_table *t: An open osl table
• struct osl_row *r: The row to get the rank of
• unsigned col_num: The number of an rbtree column
• unsigned *rank: Result pointer

See also: osl_get_nth_row().

• Standard

const char * osl_strerror(int num)

• int num: The error code

This works just like strerror(3). The given number must be an osl error code. The result must not be freed by the caller.

• The error text corresponding to an osl error code