source: mainline/uspace/srv/vfs/vfs_lookup.c

/*
 * 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 vfs
 * @{
 */

/**
 * @file vfs_lookup.c
 * @brief
 */

#include "vfs.h"
#include <macros.h>
#include <async.h>
#include <errno.h>
#include <str.h>
#include <stdarg.h>
#include <stdbool.h>
#include <fibril_synch.h>
#include <adt/list.h>
#include <vfs/canonify.h>
#include <dirent.h>
#include <assert.h>

FIBRIL_MUTEX_INITIALIZE(plb_mutex);
LIST_INITIALIZE(plb_entries);   /**< PLB entry ring buffer. */
uint8_t *plb = NULL;

static errno_t plb_insert_entry(plb_entry_t *entry, char *path, size_t *start,
    size_t len)
{
        fibril_mutex_lock(&plb_mutex);

        link_initialize(&entry->plb_link);
        entry->len = len;

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

        if (list_empty(&plb_entries)) {
                first = 0;
                last = PLB_SIZE - 1;
        } else {
                plb_entry_t *oldest = list_get_instance(
                    list_first(&plb_entries), plb_entry_t, plb_link);
                plb_entry_t *newest = list_get_instance(
                    list_last(&plb_entries), 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.
                         */
                        fibril_mutex_unlock(&plb_mutex);
                        return ELIMIT;
                }
        } else {
                if (PLB_SIZE - ((first - last) + 1) < len) {
                        /*
                         * The buffer cannot absorb the path.
                         */
                        fibril_mutex_unlock(&plb_mutex);
                        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_entries);

        fibril_mutex_unlock(&plb_mutex);

        /*
         * 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);

        *start = first;
        return EOK;
}

static void plb_clear_entry(plb_entry_t *entry, size_t first, size_t len)
{
        fibril_mutex_lock(&plb_mutex);
        list_remove(&entry->plb_link);
        /*
         * Erasing the path from PLB will come handy for debugging purposes.
         */
        size_t cnt1 = min(len, (PLB_SIZE - first) + 1);
        size_t cnt2 = len - cnt1;
        memset(&plb[first], 0, cnt1);
        memset(plb, 0, cnt2);
        fibril_mutex_unlock(&plb_mutex);
}

errno_t vfs_link_internal(vfs_node_t *base, char *path, vfs_triplet_t *child)
{
        assert(base != NULL);
        assert(child != NULL);
        assert(base->fs_handle);
        assert(child->fs_handle);
        assert(path != NULL);

        vfs_lookup_res_t res;
        char component[NAME_MAX + 1];
        errno_t rc;

        size_t len;
        char *npath = canonify(path, &len);
        if (!npath) {
                rc = EINVAL;
                goto out;
        }
        path = npath;

        vfs_triplet_t *triplet;

        char *slash = str_rchr(path, L'/');
        if (slash && slash != path) {
                if (slash[1] == 0) {
                        rc = EINVAL;
                        goto out;
                }

                memcpy(component, slash + 1, str_size(slash));
                *slash = 0;

                rc = vfs_lookup_internal(base, path, L_DIRECTORY, &res);
                if (rc != EOK)
                        goto out;
                triplet = &res.triplet;

                *slash = '/';
        } else {
                if (base->mount != NULL) {
                        rc = EINVAL;
                        goto out;
                }

                memcpy(component, path + 1, str_size(path));
                triplet = (vfs_triplet_t *) base;
        }

        if (triplet->fs_handle != child->fs_handle ||
            triplet->service_id != child->service_id) {
                rc = EXDEV;
                goto out;
        }

        async_exch_t *exch = vfs_exchange_grab(triplet->fs_handle);
        aid_t req = async_send_3(exch, VFS_OUT_LINK, triplet->service_id,
            triplet->index, child->index, NULL);

        rc = async_data_write_start(exch, component, str_size(component) + 1);
        errno_t orig_rc;
        async_wait_for(req, &orig_rc);
        vfs_exchange_release(exch);
        if (orig_rc != EOK)
                rc = orig_rc;

out:
        return rc;
}

static errno_t out_lookup(vfs_triplet_t *base, size_t *pfirst, size_t *plen,
    int lflag, vfs_lookup_res_t *result)
{
        assert(base);
        assert(result);

        errno_t rc;
        ipc_call_t answer;
        async_exch_t *exch = vfs_exchange_grab(base->fs_handle);
        aid_t req = async_send_5(exch, VFS_OUT_LOOKUP, (sysarg_t) *pfirst,
            (sysarg_t) *plen, (sysarg_t) base->service_id,
            (sysarg_t) base->index, (sysarg_t) lflag, &answer);
        async_wait_for(req, &rc);
        vfs_exchange_release(exch);

        if (rc != EOK)
                return rc;

        unsigned last = *pfirst + *plen;
        *pfirst = ipc_get_arg3(&answer) & 0xffff;
        *plen = last - *pfirst;

        result->triplet.fs_handle = (fs_handle_t) ipc_get_arg1(&answer);
        result->triplet.service_id = base->service_id;
        result->triplet.index = (fs_index_t) ipc_get_arg2(&answer);
        result->size = MERGE_LOUP32(ipc_get_arg4(&answer), ipc_get_arg5(&answer));
        result->type = (ipc_get_arg3(&answer) >> 16) ?
            VFS_NODE_DIRECTORY : VFS_NODE_FILE;
        return EOK;
}

static errno_t _vfs_lookup_internal(vfs_node_t *base, char *path, int lflag,
    vfs_lookup_res_t *result, size_t len)
{
        size_t first;
        errno_t rc;

        plb_entry_t entry;
        rc = plb_insert_entry(&entry, path, &first, len);
        if (rc != EOK)
                return rc;

        size_t next = first;
        size_t nlen = len;

        vfs_lookup_res_t res;

        /* Resolve path as long as there are mount points to cross. */
        while (nlen > 0) {
                while (base->mount) {
                        if (lflag & L_DISABLE_MOUNTS) {
                                rc = EXDEV;
                                goto out;
                        }

                        base = base->mount;
                }

                rc = out_lookup((vfs_triplet_t *) base, &next, &nlen, lflag,
                    &res);
                if (rc != EOK)
                        goto out;

                if (nlen > 0) {
                        base = vfs_node_peek(&res);
                        if (!base) {
                                rc = ENOENT;
                                goto out;
                        }
                        if (!base->mount) {
                                vfs_node_put(base);
                                rc = ENOENT;
                                goto out;
                        }
                        vfs_node_put(base);
                        if (lflag & L_DISABLE_MOUNTS) {
                                rc = EXDEV;
                                goto out;
                        }
                }
        }

        assert(nlen == 0);
        rc = EOK;

        if (result != NULL) {
                /* The found file may be a mount point. Try to cross it. */
                if (!(lflag & (L_MP | L_DISABLE_MOUNTS))) {
                        base = vfs_node_peek(&res);
                        if (base && base->mount) {
                                while (base->mount) {
                                        vfs_node_addref(base->mount);
                                        vfs_node_t *nbase = base->mount;
                                        vfs_node_put(base);
                                        base = nbase;
                                }

                                result->triplet = *((vfs_triplet_t *) base);
                                result->type = base->type;
                                result->size = base->size;
                                vfs_node_put(base);
                                goto out;
                        }
                        if (base)
                                vfs_node_put(base);
                }

                *result = res;
        }

out:
        plb_clear_entry(&entry, first, len);
        return rc;
}

/** Perform a path lookup.
 *
 * @param base    The file from which to perform the lookup.
 * @param path    Path to be resolved; it must be a NULL-terminated
 *                string.
 * @param lflag   Flags to be used during lookup.
 * @param result  Empty structure where the lookup result will be stored.
 *                Can be NULL.
 *
 * @return EOK on success or an error code from errno.h.
 *
 */
errno_t vfs_lookup_internal(vfs_node_t *base, char *path, int lflag,
    vfs_lookup_res_t *result)
{
        assert(base != NULL);
        assert(path != NULL);

        size_t len;
        errno_t rc;
        char *npath = canonify(path, &len);
        if (!npath) {
                rc = EINVAL;
                return rc;
        }
        path = npath;

        assert(path[0] == '/');

        if (lflag & (L_CREATE | L_UNLINK)) {

                /*
                 * Creation and destruction of names must be done in two
                 * separate steps: lookup of the parent node and the name
                 * link/unlink operation itself.  Otherwise the parent
                 * filesystem would not be able to tell when a mountpoint is
                 * crossed. It would attempt to perform the link/unlink in
                 * itself instead of letting the mounted filesystem do it,
                 * resulting in wrong behavior. This is the wages of server-side
                 * mountpoints.
                 */

                char *slash = str_rchr(path, L'/');
                vfs_node_t *parent = base;

                if (slash != path) {
                        int tflag = lflag;
                        vfs_lookup_res_t tres;

                        tflag &= ~(L_CREATE | L_EXCLUSIVE | L_UNLINK | L_FILE);
                        tflag |= L_DIRECTORY;
                        rc = _vfs_lookup_internal(base, path, tflag, &tres,
                            slash - path);
                        if (rc != EOK)
                                return rc;
                        parent = vfs_node_get(&tres);
                        if (!parent)
                                return ENOMEM;
                } else
                        vfs_node_addref(parent);

                rc = _vfs_lookup_internal(parent, slash, lflag, result,
                    len - (slash - path));

                vfs_node_put(parent);

        } else {
                rc = _vfs_lookup_internal(base, path, lflag, result, len);
        }

        return rc;
}

/**
 * @}
 */