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/*
 * Copyright (c) 2007 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 <sys/types.h>
#include <libadt/hash_table.h>
#include <as.h>

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

#define PLB_GET_CHAR(i)     (tmpfs_reg.plb_ro[(i) % PLB_SIZE])

#define DENTRIES_BUCKETS    256

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

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->size = 0;
    dentry->data = NULL;
    link_initialize(&dentry->dh_link);
}

/*
 * 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;

static bool tmpfs_init(void)
{
    if (!hash_table_create(&dentries, DENTRIES_BUCKETS, 1, &dentries_ops))
        return false;

    root = (tmpfs_dentry_t *) malloc(sizeof(tmpfs_dentry_t));
    if (!root)
        return false;
    tmpfs_dentry_initialize(root);
    root->index = tmpfs_next_index++;
    root->name = "";
    root->type = TMPFS_DIRECTORY;
    hash_table_insert(&dentries, &root->index, &root->dh_link);

    /*
     * This is only for debugging. Once we can create files and directories
     * using VFS, we can get rid of this.
     */
    tmpfs_dentry_t *d;
    d = (tmpfs_dentry_t *) malloc(sizeof(tmpfs_dentry_t));
    if (!d) {
        free(root);
        root = NULL;
        return false;
    }
    tmpfs_dentry_initialize(d);
    d->index = tmpfs_next_index++;
    root->child = d;
    d->parent = root;
    d->type = TMPFS_DIRECTORY;
    d->name = "dir1";
    hash_table_insert(&dentries, &d->index, &d->dh_link);

    d = (tmpfs_dentry_t *) malloc(sizeof(tmpfs_dentry_t));
    if (!d) {
        free(root->child);
        free(root);
        root = NULL;
        return false;
    }
    tmpfs_dentry_initialize(d);
    d->index = tmpfs_next_index++;
    root->child->sibling = d;
    d->parent = root;
    d->type = TMPFS_DIRECTORY;
    d->name = "dir2";
    hash_table_insert(&dentries, &d->index, &d->dh_link);
    
    d = (tmpfs_dentry_t *) malloc(sizeof(tmpfs_dentry_t));
    if (!d) {
        free(root->child->sibling);
        free(root->child);
        free(root);
        root = NULL;
        return false;
    }
    tmpfs_dentry_initialize(d);
    d->index = tmpfs_next_index++;
    root->child->child = d;
    d->parent = root->child;
    d->type = TMPFS_FILE;
    d->name = "file1";
    d->data = "This is the contents of /dir1/file1.\n";
    d->size = strlen(d->data);
    hash_table_insert(&dentries, &d->index, &d->dh_link);

    d = (tmpfs_dentry_t *) malloc(sizeof(tmpfs_dentry_t));
    if (!d) {
        free(root->child->sibling);
        free(root->child->child);
        free(root->child);
        free(root);
        root = NULL;
        return false;
    }
    tmpfs_dentry_initialize(d);
    d->index = tmpfs_next_index++;
    root->child->sibling->child = d;
    d->parent = root->child->sibling;
    d->type = TMPFS_FILE;
    d->name = "file2";
    d->data = "This is the contents of /dir2/file2.\n";
    d->size = strlen(d->data);
    hash_table_insert(&dentries, &d->index, &d->dh_link);

    return true;
}

/** Compare one component of path to a directory entry.
 *
 * @param dentry    Directory entry to compare the path component with.
 * @param start     Index into PLB where the path component starts.
 * @param last      Index of the last character of the path in PLB.
 *
 * @return      Zero on failure or delta such that (index + delta) %
 *          PLB_SIZE points to the first unprocessed character in
 *          PLB which comprises the path.
 */
static unsigned match_path_component(tmpfs_dentry_t *dentry, unsigned start,
    unsigned last)
{
    int i, j;
    size_t namelen;

    namelen = strlen(dentry->name);

    if (last < start)
        last += PLB_SIZE;

    for (i = 0, j = start; i < namelen && j <= last; i++, j++) {
        if (dentry->name[i] != PLB_GET_CHAR(j))
            return 0;
    }
    
    if (i != namelen)
        return 0;
    if (j < last && PLB_GET_CHAR(j) != '/')
        return 0;
    if (j == last)
            return 0;
    
    return (j - start);
}

void tmpfs_lookup(ipc_callid_t rid, ipc_call_t *request)
{
    unsigned next = IPC_GET_ARG1(*request);
    unsigned last = IPC_GET_ARG2(*request);
    int dev_handle = IPC_GET_ARG3(*request);

    if (last < next)
        last += PLB_SIZE;

    if (!root && !tmpfs_init()) {
        ipc_answer_0(rid, ENOMEM);
        return;
    }

    tmpfs_dentry_t *dtmp = root->child; 
    tmpfs_dentry_t *dcur = root;

    bool hit = true;
    
    if (PLB_GET_CHAR(next) == '/')
        next++;     /* eat slash */
    
    while (next <= last) {
        unsigned delta;
        hit = false;
        do {
            delta = match_path_component(dtmp, next, last);
            if (!delta) {
                dtmp = dtmp->sibling;
            } else {
                hit = true;
                next += delta;
                next++;     /* eat slash */
                dcur = dtmp;
                dtmp = dtmp->child;
            }   
        } while (delta == 0 && dtmp);
        if (!hit) {
            ipc_answer_3(rid, ENOENT, tmpfs_reg.fs_handle,
                dev_handle, dcur->index);
            return;
        }
    }

    ipc_answer_3(rid, EOK, tmpfs_reg.fs_handle, dev_handle, dcur->index);
}

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 = max(0, min(dentry->size - pos, len));
    (void) ipc_data_read_finalize(callid, dentry->data + pos, bytes);

    /*
     * 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_1(rid, EOK, len);
        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_1(rid, EOK, 0);
        return;
    }
    dentry->size += delta;
    dentry->data = newdata;
    (void) ipc_data_write_finalize(callid, dentry->data + pos, len);
    ipc_answer_1(rid, EOK, len);
}

/**
 * @}
 */