source: mainline/uspace/srv/vfs/vfs_lookup.c@ 20614d0

/*
 * 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        vfs.c
 * @brief       VFS_LOOKUP method and Path Lookup Buffer code.
 */

#include <ipc/ipc.h>
#include <async.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <bool.h>
#include <futex.h>
#include <libadt/list.h>
#include "vfs.h"

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

atomic_t plb_futex = FUTEX_INITIALIZER;
link_t plb_head;        /**< PLB entry ring buffer. */
uint8_t *plb = NULL;

/** Perform a path lookup.
 *
 * @param path          Path to be resolved; it needn't be an ASCIIZ string.
 * @param len           Number of path characters pointed by path.
 * @param result        Empty node structure where the result will be stored.
 * @param altroot       If non-empty, will be used instead of rootfs as the root
 *                      of the whole VFS tree.
 *
 * @return              EOK on success or an error code from errno.h.
 */
int vfs_lookup_internal(char *path, size_t len, vfs_triplet_t *result,
    vfs_pair_t *altroot)
{
        vfs_pair_t *root;

        if (!len)
                return EINVAL;

        if (altroot)
                root = altroot;
        else
                root = (vfs_pair_t *) &rootfs;

        if (!root->fs_handle)
                return ENOENT;
        
        futex_down(&plb_futex);

        plb_entry_t entry;
        link_initialize(&entry.plb_link);
        entry.len = len;

        off_t first;    /* the first free index */
        off_t last;     /* the last free index */

        if (list_empty(&plb_head)) {
                first = 0;
                last = PLB_SIZE - 1;
        } else {
                plb_entry_t *oldest = list_get_instance(plb_head.next,
                    plb_entry_t, plb_link);
                plb_entry_t *newest = list_get_instance(plb_head.prev,
                    plb_entry_t, plb_link);

                first = (newest->index + newest->len) % PLB_SIZE;
                last = (oldest->index - 1) % PLB_SIZE;
        }

        if (first <= last) {
                if ((last - first) + 1 < len) {
                        /*
                         * The buffer cannot absorb the path.
                         */
                        futex_up(&plb_futex);
                        return ELIMIT;
                }
        } else {
                if (PLB_SIZE - ((first - last) + 1) < len) {
                        /*
                         * The buffer cannot absorb the path.
                         */
                        futex_up(&plb_futex);
                        return ELIMIT;
                }
        }

        /*
         * We know the first free index in PLB and we also know that there is
         * enough space in the buffer to hold our path.
         */

        entry.index = first;
        entry.len = len;

        /*
         * Claim PLB space by inserting the entry into the PLB entry ring
         * buffer.
         */
        list_append(&entry.plb_link, &plb_head);
        
        futex_up(&plb_futex);

        /*
         * Copy the path into PLB.
         */
        size_t cnt1 = min(len, (PLB_SIZE - first) + 1);
        size_t cnt2 = len - cnt1;
        
        memcpy(&plb[first], path, cnt1);
        memcpy(plb, &path[cnt1], cnt2);

        ipc_call_t answer;
        int phone = vfs_grab_phone(root->fs_handle);
        aid_t req = async_send_3(phone, VFS_LOOKUP, (ipcarg_t) first,
            (ipcarg_t) last, (ipcarg_t) root->dev_handle, &answer);
        vfs_release_phone(phone);

        ipcarg_t rc;
        async_wait_for(req, &rc);

        futex_down(&plb_futex);
        list_remove(&entry.plb_link);
        /*
         * Erasing the path from PLB will come handy for debugging purposes.
         */
        memset(&plb[first], 0, cnt1);
        memset(plb, 0, cnt2);
        futex_up(&plb_futex);

        if (rc == EOK) {
                result->fs_handle = (int) IPC_GET_ARG1(answer);
                result->dev_handle = (int) IPC_GET_ARG2(answer);
                result->index = (int) IPC_GET_ARG3(answer);
        }

        return rc;
}

/**
 * @}
 */