web: Fix typo in README.

[osl.git] / osl.h.in

/*
 * Copyright (C) 2007-2009 Andre Noll <maan@tuebingen.mpg.de>
 *
 * Licensed under the GPL v2. For licencing details see COPYING.
 */

/** \file osl.h User interface for the object storage layer. */

#include <sys/mman.h>
#include <inttypes.h>

/** Export all declarations in this file. */
#pragma GCC visibility push(default)

/** Describes an object of the object storage layer (osl) */
struct osl_object {
        /** Pointer to the data of the object. */
        void *data;
        /** The object's size. */
        size_t size;
};

/** Flags that change the internal handling of osl tables. */
enum osl_table_flags {
        /** This table will have many rows. */
        OSL_LARGE_TABLE = 1
};

/** The three different types of storage for an osl column */
enum osl_storage_type {
        /**
         * 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_MAPPED_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_DISK_STORAGE,
        /**
         * Objects for columns of this type are volatile: They are only stored
         * in memory and are discarded when the table is closed.
         */
        OSL_NO_STORAGE
};

/**
 * Additional per-column flags
 */
enum osl_storage_flags {
        /**
         * Build an rbtree for this column. This is only possible if the
         * storage type of the column is either \a OSL_MAPPED_STORAGE or \a
         * OSL_NO_STORAGE. In order to lookup objects in the table by using \a
         * osl_get_row(), the lookup column must have an associated rbtree.
         *
         * \sa osl_storage_type, osl_get_row()
         */
        OSL_RBTREE = 1,
        /** The data for this column will have constant size. */
        OSL_FIXED_SIZE = 2,
        /** All values are different. Must be set if \p OSL_RBTREE is set. */
        OSL_UNIQUE = 4,
        /** Do not free the data for this column (\p OSL_NO_STORAGE). */
        OSL_DONT_FREE = 8
};

/** Opaque osl table structure. */
struct osl_table;
/** Opaque osl row structure. */
struct osl_row;

/**
 * In order to build up 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_compare_func(const struct osl_object *obj1,
        const struct osl_object *obj2);

/**
 * The osl_rbreee_loop functions take a function pointer of this type. For each
 * node in the rbtree, the given function is called.
 *
 * \sa osl_rbtree_loop(), osl_rbtree_loop_reverse().
 */
typedef int osl_rbtree_loop_func(struct osl_row *row, void *data);

/**
 * Describes one column of a osl table.
 */
struct osl_column_description {
        /** One of the three possible types of storage, \sa osl_storage_type. */
        uint16_t storage_type;
        /** Specifies further properties of the column, \sa osl_storage_flags. */
        uint16_t storage_flags;
        /**
         * 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 \a NO_STORAGE.
         */
        char *name;
        /**
         * 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.
         *
         * \sa osl_storage_flags, osl_compare_func
         */
        osl_compare_func *compare_function;
        /**
         * If the \a 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 \a OSL_FIXED_SIZE is not set.
         */
        uint32_t data_size;
};

/**
 * Describes one osl table.
 *
 * A pointer to the table description is passed to \ref osl_create_table() and
 * \ref 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.
 */
struct osl_table_description {
        /**
         * The directory which contains all files of this table. This may be
         * either relative to the cwd or an absolute path.
         */
        const char *dir;
        /**
         * The table name. A subdirectory of \a dir called \a name is created
         * at table creation time. It must be a valid name for a subdirectory.
         * In particular, no slashes are allowed for \a name.
         */
        const char *name;
        /** The number of columns of this table. */
        uint16_t num_columns;
        /** Further table-wide information, \sa osl_table_flags. */
        uint8_t flags;
        /** The array describing the individual columns of the table. */
        struct osl_column_description *column_descriptions;
};

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

/**
 * Create a new osl table.
 *
 * \param desc Pointer to the table description.
 *
 * \return Standard.
 */
int osl_create_table(const struct osl_table_description *desc);

/**
 * Open an osl table.
 *
 * Each osl table must be opened before its data can be accessed.
 *
 * \param desc Describes the table to be opened.
 * \param result Contains a pointer to the open table on success.
 *
 * The table description given by \a desc should coincide with the
 * description used at creation time.
 *
 * \return Standard.
 */
int osl_open_table(const struct osl_table_description *desc,
        struct osl_table **result);

/**
 * Close an osl table.
 *
 * \param t Pointer to the table to be closed.
 * \param 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().
 *
 * \return Standard.
 *
 * \sa osl_open_table(), unmap_table().
 */
int osl_close_table(struct osl_table *t, enum osl_close_flags flags);

/**
 * Get the row that contains the given object.
 *
 * \param t Pointer to an open osl table.
 * \param col_num The number of the column to be searched.
 * \param obj The object to be looked up.
 * \param result Points to the row containing \a obj.
 *
 * Lookup \a obj in \a t and return the row containing \a obj. The column
 * specified by \a col_num must have an associated rbtree.
 *
 * \return Standard. \a result is set to \p NULL if and only if the function
 * returns negative.
 *
 * \sa osl_storage_flags
 */
int osl_get_row(const struct osl_table *t, unsigned col_num,
        const struct osl_object *obj, struct osl_row **result);

/**
 * Retrieve an object identified by row and column.
 *
 * \param t Pointer to an open osl table.
 * \param row Pointer to the row.
 * \param col_num The column number.
 * \param object The result pointer.
 *
 * The column determined by \a col_num must be of type \p OSL_MAPPED_STORAGE
 * or \p OSL_NO_STORAGE, i.e. no disk storage objects may be retrieved by this
 * function.
 *
 * \return Standard.
 *
 * \sa osl_storage_type, osl_open_disk_object().
 */
int osl_get_object(const struct osl_table *t, const struct osl_row *row,
        unsigned col_num, struct osl_object *object);

/**
 * Retrieve an object of type \p OSL_DISK_STORAGE by row and column.
 *
 * \param t Pointer to an open osl table.
 * \param r Pointer to the row containing the object.
 * \param col_num The column number.
 * \param obj Points to the result upon successful return.
 *
 * For columns of type \p 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.
 *
 * \return Standard.
 *
 * \sa osl_get_object(), osl_storage_type, osl_close_disk_object().
 */
int osl_open_disk_object(const struct osl_table *t,
        const struct osl_row *r, unsigned col_num, struct osl_object *obj);

/**
 * Free resources that were allocated during osl_open_disk_object().
 *
 * \param obj Pointer to the object previously returned by open_disk_object().
 *
 * \return The return value of the underlying call to munmap().
 *
 * \sa munmap(2).
 */
int osl_close_disk_object(struct osl_object *obj);

/**
 * Add a new row to an osl table and retrieve this row.
 *
 * \param t Pointer to an open osl table.
 * \param objects Array of objects to be added.
 * \param row Result pointer.
 *
 * The \a 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 \a 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).
 *
 * It is considered an error if an object is added to a column with associated
 * rbtree if this object is equal to an object already contained in that column
 * (i.e. the compare function for the column's rbtree returns zero).
 *
 * \return Standard.
 *
 * \sa struct osl_table_description, osl_compare_func, osl_add_row().
 */
int osl_add_and_get_row(struct osl_table *t, struct osl_object *objects,
        struct osl_row **row);

/**
 * Add a new row to an osl table.
 *
 * \param t Same meaning as osl_add_and_get_row().
 * \param objects Same meaning as osl_add_and_get_row().
 *
 * \return The return value of the underlying call to osl_add_and_get_row().
 *
 * This is equivalent to osl_add_and_get_row(t, objects, NULL).
 */
int osl_add_row(struct osl_table *t, struct osl_object *objects);

/**
 * Delete a row from an osl table.
 *
 * \param t Pointer to an open osl table.
 * \param 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.
 *
 * \return Standard.
 */
int osl_del_row(struct osl_table *t, struct osl_row *row);

/**
 * Loop over all nodes in an rbtree.
 *
 * \param t Pointer to an open osl table.
 * \param col_num The column to use for iterating over the elements.
 * \param private_data Pointer that gets passed to \a func.
 * \param func The function to be called for each node in the rbtree.
 *
 * This function does an in-order walk of the rbtree associated with \a
 * col_num. It is an error if the \p OSL_RBTREE flag is not set for this
 * column. For each node in the rbtree, the given function \a 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 \a private_data pointer is passed verbatim to \a func as the
 * second argument. The loop terminates either if \a func returns a negative
 * value, or if all nodes of the tree have been visited.
 *
 * \return Standard. If the termination of the loop was caused by \a func
 * returning a negative value, \p -E_OSL_LOOP is returned. This is the only
 * possible error.
 *
 * \sa osl_storage_flags, osl_rbtree_loop_reverse(), osl_compare_func.
 */
int osl_rbtree_loop(const struct osl_table *t, unsigned col_num,
        void *private_data, osl_rbtree_loop_func *func);

/**
 * Loop over all nodes in an rbtree in reverse order.
 *
 * \param t Identical meaning as in \p osl_rbtree_loop().
 * \param col_num Identical meaning as in \p osl_rbtree_loop().
 * \param private_data Identical meaning as in \p osl_rbtree_loop().
 * \param func Identical meaning as in \p osl_rbtree_loop().
 *
 * This function is identical to \p osl_rbtree_loop(), the only difference
 * is that the tree is walked in reverse order.
 *
 * \return The same return value as \p osl_rbtree_loop().
 *
 * \sa osl_rbtree_loop().
 */
int osl_rbtree_loop_reverse(const struct osl_table *t, unsigned col_num,
        void *private_data, osl_rbtree_loop_func *func);

/**
 * Change an object in an osl table.
 *
 * \param t Pointer to an open osl table.
 * \param r Pointer to the row containing the object to be updated.
 * \param col_num Number of the column containing the object to be updated.
 * \param 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 \a
 * col_num. It then inserts \a obj into the table and the rbtree if necessary.
 *
 * If the \p OSL_RBTREE flag is set for \a col_num, you \b MUST call this
 * function in order to change the contents of an object, even for volatile or
 * mapped columns of constant size (which may be updated directly if \p
 * OSL_RBTREE is not set). Otherwise the rbtree might become corrupt.
 *
 * \return Standard
 */
int osl_update_object(struct osl_table *t, const struct osl_row *r,
        unsigned col_num, struct osl_object *obj);

/**
 * Get the number of rows of the given table.
 *
 * \param t Pointer to an open osl table.
 * \param num_rows Result is returned here.
 *
 * The number of rows returned via \a num_rows excluding any invalid rows.
 *
 * \return Positive on success, \p -E_OSL_BAD_TABLE if \a t is \p NULL.
 */
int osl_get_num_rows(const struct osl_table *t, unsigned *num_rows);

/**
 * Get the row corresponding to the smallest rbtree node of a column.
 *
 * \param t An open rbtree table.
 * \param col_num The number of the rbtree column.
 * \param 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 \a col_num refers to a column without an
 * associated rbtree.
 *
 * \return Standard.
 *
 * \sa osl_get_nth_row(), osl_rbtree_last_row().
 */
int osl_rbtree_first_row(const struct osl_table *t, unsigned col_num,
        struct osl_row **result);

/**
 * Get the row corresponding to the greatest rbtree node of a column.
 *
 * \param t The same meaning as in \p osl_rbtree_first_row().
 * \param col_num The same meaning as in \p osl_rbtree_first_row().
 * \param result The same meaning as in \p osl_rbtree_first_row().
 *
 * 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.
 *
 * \return Standard.
 *
 * \sa osl_get_nth_row(), osl_rbtree_first_row().
 */
int osl_rbtree_last_row(const struct osl_table *t, unsigned col_num,
        struct osl_row **result);

/**
 * Get the row with n-th greatest value.
 *
 * \param t Pointer to an open osl table.
 * \param col_num The column number.
 * \param n The rank of the desired row.
 * \param result Row is returned here.
 *
 * Retrieve the n-th order statistic with respect to the compare function
 * of the rbtree column \a col_num. In other words, get the row with
 * \a n th greatest value in column \a col_num. It is an error if
 * \a col_num is not a rbtree column, or if \a n is larger than the
 * number of rows in the table.
 *
 * \return Standard.
 *
 * \sa osl_storage_flags, osl_compare_func, osl_get_row(),
 * osl_rbtree_last_row(), osl_rbtree_first_row(), osl_get_rank().
 */
int osl_get_nth_row(const struct osl_table *t, unsigned col_num,
        unsigned n, struct osl_row **result);

/**
 * Get the rank of a row.
 *
 * \param t An open osl table.
 * \param r The row to get the rank of.
 * \param col_num The number of an rbtree column.
 * \param rank Result pointer.
 *
 * 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 column
 * number \a col_num of \a table.
 *
 * \return Standard.
 *
 * \sa osl_get_nth_row().
 */
int osl_get_rank(const struct osl_table *t, struct osl_row *r,
        unsigned col_num, unsigned *rank);

/**
 * Get a string describing the error code passed in the argument.
 *
 * \param 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.
 *
 * \return The error text corresponding to an osl error code.
 */
const char *osl_strerror(int num);

#pragma GCC visibility pop