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/*
 * Copyright (c) 2008 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup fs
 * @{
 */ 

/**
 * @file    tmpfs_ops.c
 * @brief   Implementation of VFS operations for the TMPFS file system
 *      server.
 */

#include "tmpfs.h"
#include "../../vfs/vfs.h"
#include <ipc/ipc.h>
#include <async.h>
#include <errno.h>
#include <atomic.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <assert.h>
#include <sys/types.h>
#include <libadt/hash_table.h>
#include <as.h>
#include <libfs.h>

#define min(a, b)       ((a) < (b) ? (a) : (b))
#define max(a, b)       ((a) > (b) ? (a) : (b))

#define DENTRIES_BUCKETS    256

/*
 * For now, we don't distinguish between different dev_handles/instances. All
 * requests resolve to the only instance, rooted in the following variable.
 */
static tmpfs_dentry_t *root;

/*
 * Implementation of the libfs interface.
 */

/* Forward declarations of static functions. */
static bool tmpfs_match(void *, const char *);
static void *tmpfs_create_node(int);
static bool tmpfs_link_node(void *, void *, const char *);
static int tmpfs_unlink_node(void *);
static void tmpfs_destroy_node(void *);

/* Implementation of helper functions. */
static unsigned long tmpfs_index_get(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->index;
}

static unsigned long tmpfs_size_get(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->size;
}

static unsigned tmpfs_lnkcnt_get(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->lnkcnt;
}

static void *tmpfs_child_get(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->child;
}

static void *tmpfs_sibling_get(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->sibling;
}

static void *tmpfs_root_get(void)
{
    return root; 
}

static char tmpfs_plb_get_char(unsigned pos)
{
    return tmpfs_reg.plb_ro[pos % PLB_SIZE];
}

static bool tmpfs_is_directory(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->type == TMPFS_DIRECTORY;
}

static bool tmpfs_is_file(void *nodep)
{
    return ((tmpfs_dentry_t *) nodep)->type == TMPFS_FILE;
}

/** libfs operations */
libfs_ops_t tmpfs_libfs_ops = {
    .match = tmpfs_match,
    .create = tmpfs_create_node,
    .destroy = tmpfs_destroy_node,
    .link = tmpfs_link_node,
    .unlink = tmpfs_unlink_node,
    .index_get = tmpfs_index_get,
    .size_get = tmpfs_size_get,
    .lnkcnt_get = tmpfs_lnkcnt_get,
    .child_get = tmpfs_child_get,
    .sibling_get = tmpfs_sibling_get,
    .root_get = tmpfs_root_get,
    .plb_get_char = tmpfs_plb_get_char,
    .is_directory = tmpfs_is_directory,
    .is_file = tmpfs_is_file
};

/** Hash table of all directory entries. */
hash_table_t dentries;

/* Implementation of hash table interface. */
static hash_index_t dentries_hash(unsigned long *key)
{
    return *key % DENTRIES_BUCKETS;
}

static int dentries_compare(unsigned long *key, hash_count_t keys,
    link_t *item)
{
    tmpfs_dentry_t *dentry = hash_table_get_instance(item, tmpfs_dentry_t,
        dh_link);
    return dentry->index == *key;
}

static void dentries_remove_callback(link_t *item)
{
}

/** TMPFS dentries hash table operations. */
hash_table_operations_t dentries_ops = {
    .hash = dentries_hash,
    .compare = dentries_compare,
    .remove_callback = dentries_remove_callback
};

unsigned tmpfs_next_index = 1;

static void tmpfs_dentry_initialize(tmpfs_dentry_t *dentry)
{
    dentry->index = 0;
    dentry->parent = NULL;
    dentry->sibling = NULL;
    dentry->child = NULL;
    dentry->name = NULL;
    dentry->type = TMPFS_NONE;
    dentry->lnkcnt = 0;
    dentry->size = 0;
    dentry->data = NULL;
    link_initialize(&dentry->dh_link);
}

static bool tmpfs_init(void)
{
    if (!hash_table_create(&dentries, DENTRIES_BUCKETS, 1, &dentries_ops))
        return false;
    root = (tmpfs_dentry_t *) tmpfs_create_node(L_DIRECTORY);
    root->lnkcnt = 1;
    return root != NULL;
}

/** Compare one component of path to a directory entry.
 *
 * @param nodep     Node to compare the path component with.
 * @param component Array of characters holding component name.
 *
 * @return      True on match, false otherwise.
 */
bool tmpfs_match(void *nodep, const char *component)
{
    tmpfs_dentry_t *dentry = (tmpfs_dentry_t *) nodep;

    return !strcmp(dentry->name, component);
}

void *tmpfs_create_node(int lflag)
{
    assert((lflag & L_FILE) ^ (lflag & L_DIRECTORY));

    tmpfs_dentry_t *node = malloc(sizeof(tmpfs_dentry_t));
    if (!node)
        return NULL;

    tmpfs_dentry_initialize(node);
    node->index = tmpfs_next_index++;
    if (lflag & L_DIRECTORY) 
        node->type = TMPFS_DIRECTORY;
    else 
        node->type = TMPFS_FILE;

    /* Insert the new node into the dentry hash table. */
    hash_table_insert(&dentries, &node->index, &node->dh_link);
    return (void *) node;
}

bool tmpfs_link_node(void *prnt, void *chld, const char *nm)
{
    tmpfs_dentry_t *parentp = (tmpfs_dentry_t *) prnt;
    tmpfs_dentry_t *childp = (tmpfs_dentry_t *) chld;

    assert(parentp->type == TMPFS_DIRECTORY);

    size_t len = strlen(nm);
    char *name = malloc(len + 1);
    if (!name)
        return false;
    
    childp->lnkcnt++;
    
    strcpy(name, nm);
    childp->name = name;

    /* Insert the new node into the namespace. */
    if (parentp->child) {
        tmpfs_dentry_t *tmp = parentp->child;
        while (tmp->sibling)
            tmp = tmp->sibling;
        tmp->sibling = childp;
    } else {
        parentp->child = childp;
    }
    childp->parent = parentp;

    return true;
}

int tmpfs_unlink_node(void *nodeptr)
{
    tmpfs_dentry_t *dentry = (tmpfs_dentry_t *)nodeptr;

    if (dentry->child)
        return ENOTEMPTY;

    if (!dentry->parent)
        return EBUSY;

    if (dentry->parent->child == dentry) {
        dentry->parent->child = dentry->sibling;
    } else {
        /* TODO: consider doubly linked list for organizing siblings. */
        tmpfs_dentry_t *tmp = dentry->parent->child;
        while (tmp->sibling != dentry)
            tmp = tmp->sibling;
        tmp->sibling = dentry->sibling;
    }
    dentry->sibling = NULL;
    dentry->parent = NULL;

    free(dentry->name);
    dentry->name = NULL;

    dentry->lnkcnt--;

    return EOK;
}

void tmpfs_destroy_node(void *nodep)
{
    tmpfs_dentry_t *dentry = (tmpfs_dentry_t *) nodep;
    
    assert(!dentry->lnkcnt);
    assert(!dentry->child);
    assert(!dentry->sibling);

    unsigned long index = dentry->index;
    hash_table_remove(&dentries, &index, 1);

    if (dentry->type == TMPFS_FILE)
        free(dentry->data);
    free(dentry);
}

void tmpfs_lookup(ipc_callid_t rid, ipc_call_t *request)
{
    /* Initialize TMPFS. */
    if (!root && !tmpfs_init()) {
        ipc_answer_0(rid, ENOMEM);
        return;
    }
    libfs_lookup(&tmpfs_libfs_ops, tmpfs_reg.fs_handle, rid, request);
}

void tmpfs_read(ipc_callid_t rid, ipc_call_t *request)
{
    int dev_handle = IPC_GET_ARG1(*request);
    unsigned long index = IPC_GET_ARG2(*request);
    off_t pos = IPC_GET_ARG3(*request);

    /*
     * Lookup the respective dentry.
     */
    link_t *hlp;
    hlp = hash_table_find(&dentries, &index);
    if (!hlp) {
        ipc_answer_0(rid, ENOENT);
        return;
    }
    tmpfs_dentry_t *dentry = hash_table_get_instance(hlp, tmpfs_dentry_t,
        dh_link);

    /*
     * Receive the read request.
     */
    ipc_callid_t callid;
    size_t len;
    if (!ipc_data_read_receive(&callid, &len)) {
        ipc_answer_0(callid, EINVAL);   
        ipc_answer_0(rid, EINVAL);
        return;
    }

    size_t bytes;
    if (dentry->type == TMPFS_FILE) {
        bytes = max(0, min(dentry->size - pos, len));
        (void) ipc_data_read_finalize(callid, dentry->data + pos,
            bytes);
    } else {
        int i;
        tmpfs_dentry_t *cur;
        
        assert(dentry->type == TMPFS_DIRECTORY);
        
        /*
         * Yes, we really use O(n) algorithm here.
         * If it bothers someone, it could be fixed by introducing a
         * hash table.
         */
        for (i = 0, cur = dentry->child; i < pos && cur; i++,
            cur = cur->sibling)
            ;

        if (!cur) {
            ipc_answer_0(callid, ENOENT);
            ipc_answer_1(rid, ENOENT, 0);
            return;
        }

        (void) ipc_data_read_finalize(callid, cur->name,
            strlen(cur->name) + 1);
        bytes = 1;
    }

    /*
     * Answer the VFS_READ call.
     */
    ipc_answer_1(rid, EOK, bytes);
}

void tmpfs_write(ipc_callid_t rid, ipc_call_t *request)
{
    int dev_handle = IPC_GET_ARG1(*request);
    unsigned long index = IPC_GET_ARG2(*request);
    off_t pos = IPC_GET_ARG3(*request);

    /*
     * Lookup the respective dentry.
     */
    link_t *hlp;
    hlp = hash_table_find(&dentries, &index);
    if (!hlp) {
        ipc_answer_0(rid, ENOENT);
        return;
    }
    tmpfs_dentry_t *dentry = hash_table_get_instance(hlp, tmpfs_dentry_t,
        dh_link);

    /*
     * Receive the write request.
     */
    ipc_callid_t callid;
    size_t len;
    if (!ipc_data_write_receive(&callid, &len)) {
        ipc_answer_0(callid, EINVAL);   
        ipc_answer_0(rid, EINVAL);
        return;
    }

    /*
     * Check whether the file needs to grow.
     */
    if (pos + len <= dentry->size) {
        /* The file size is not changing. */
        (void) ipc_data_write_finalize(callid, dentry->data + pos, len);
        ipc_answer_2(rid, EOK, len, dentry->size);
        return;
    }
    size_t delta = (pos + len) - dentry->size;
    /*
     * At this point, we are deliberately extremely straightforward and
     * simply realloc the contents of the file on every write that grows the
     * file. In the end, the situation might not be as bad as it may look:
     * our heap allocator can save us and just grow the block whenever
     * possible.
     */
    void *newdata = realloc(dentry->data, dentry->size + delta);
    if (!newdata) {
        ipc_answer_0(callid, ENOMEM);
        ipc_answer_2(rid, EOK, 0, dentry->size);
        return;
    }
    /* Clear any newly allocated memory in order to emulate gaps. */
    memset(newdata + dentry->size, 0, delta);
    dentry->size += delta;
    dentry->data = newdata;
    (void) ipc_data_write_finalize(callid, dentry->data + pos, len);
    ipc_answer_2(rid, EOK, len, dentry->size);
}

void tmpfs_truncate(ipc_callid_t rid, ipc_call_t *request)
{
    int dev_handle = IPC_GET_ARG1(*request);
    unsigned long index = IPC_GET_ARG2(*request);
    size_t size = IPC_GET_ARG3(*request);

    /*
     * Lookup the respective dentry.
     */
    link_t *hlp;
    hlp = hash_table_find(&dentries, &index);
    if (!hlp) {
        ipc_answer_0(rid, ENOENT);
        return;
    }
    tmpfs_dentry_t *dentry = hash_table_get_instance(hlp, tmpfs_dentry_t,
        dh_link);

    if (size == dentry->size) {
        ipc_answer_0(rid, EOK);
        return;
    }

    void *newdata = realloc(dentry->data, size);
    if (!newdata) {
        ipc_answer_0(rid, ENOMEM);
        return;
    }
    if (size > dentry->size) {
        size_t delta = size - dentry->size;
        memset(newdata + dentry->size, 0, delta);
    }
    dentry->size = size;
    dentry->data = newdata;
    ipc_answer_0(rid, EOK);
}

void tmpfs_destroy(ipc_callid_t rid, ipc_call_t *request)
{
    int dev_handle = IPC_GET_ARG1(*request);
    unsigned long index = IPC_GET_ARG2(*request);

    link_t *hlp;
    hlp = hash_table_find(&dentries, &index);
    if (!hlp) {
        ipc_answer_0(rid, ENOENT);
        return;
    }
    tmpfs_dentry_t *dentry = hash_table_get_instance(hlp, tmpfs_dentry_t,
        dh_link);
    tmpfs_destroy_node(dentry);
    ipc_answer_0(rid, EOK);
}

/**
 * @}
 */