source: mainline/uspace/srv/vfs/vfs_mount.c@ a806bd61

/*
 * 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_mount.c
 * @brief       VFS_MOUNT method.
 */

#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"

atomic_t rootfs_futex = FUTEX_INITIALIZER;
vfs_triplet_t rootfs = {
        .fs_handle = 0,
        .dev_handle = 0,
        .index = 0,
};

static int lookup_root(int fs_handle, int dev_handle, vfs_triplet_t *root)
{
        vfs_pair_t altroot = {
                .fs_handle = fs_handle,
                .dev_handle = dev_handle,
        };

        return vfs_lookup_internal("/", strlen("/"), root, &altroot);
}

void vfs_mount(ipc_callid_t rid, ipc_call_t *request)
{
        int dev_handle;
        vfs_node_t *mp_node = NULL;

        /*
         * We expect the library to do the device-name to device-handle
         * translation for us, thus the device handle will arrive as ARG1
         * in the request.
         */
        dev_handle = IPC_GET_ARG1(*request);

        /*
         * For now, don't make use of ARG2 and ARG3, but they can be used to
         * carry mount options in the future.
         */

        /*
         * Now, we expect the client to send us data with the name of the file
         * system and the path of the mountpoint.
         */
        ipc_callid_t callid;
        size_t size;
        if (!ipc_data_receive(&callid, NULL, &size)) {
                ipc_answer_0(callid, EINVAL);
                ipc_answer_0(rid, EINVAL);
                return;
        }

        /*
         * There is no sense in receiving data that can't hold a single
         * character of path. We won't accept data that exceed certain limits
         * either.
         */
        if ((size < FS_NAME_MAXLEN + 1) ||
            (size > FS_NAME_MAXLEN + MAX_PATH_LEN)) {
                ipc_answer_0(callid, EINVAL);
                ipc_answer_0(rid, EINVAL);
                return;
        }

        /*
         * Allocate buffer for the data being received.
         */
        uint8_t *buf;
        buf = malloc(size);
        if (!buf) {
                ipc_answer_0(callid, ENOMEM);
                ipc_answer_0(rid, ENOMEM);
                return;
        }

        /*
         * Deliver the data.
         */
        (void) ipc_data_deliver(callid, buf, size);

        char fs_name[FS_NAME_MAXLEN + 1];
        memcpy(fs_name, buf, FS_NAME_MAXLEN);
        fs_name[FS_NAME_MAXLEN] = '\0';

        /*
         * Check if we know a file system with the same name as is in fs_name.
         * This will also give us its file system handle.
         */
        int fs_handle = fs_name_to_handle(fs_name, true);
        if (!fs_handle) {
                free(buf);
                ipc_answer_0(rid, ENOENT);
                return;
        }

        /*
         * Lookup the root node of the filesystem being mounted.
         * In this case, we don't need to take the unlink_futex as the root node
         * cannot be removed. However, we do take a reference to it so that
         * we can track how many times it has been mounted.
         */
        int rc;
        vfs_triplet_t mounted_root;
        rc = lookup_root(fs_handle, dev_handle, &mounted_root);
        if (rc != EOK) {
                free(buf);
                ipc_answer_0(rid, rc);
                return;
        }
        vfs_node_t *mr_node = vfs_node_get(&mounted_root);
        if (!mr_node) {
                free(buf);
                ipc_answer_0(rid, ENOMEM);
                return;
        }

        /*
         * Finally, we need to resolve the path to the mountpoint. 
         */
        vfs_triplet_t mp;
        futex_down(&rootfs_futex);
        if (rootfs.fs_handle) {
                /*
                 * We already have the root FS.
                 */
                futex_down(&unlink_futex);
                rc = vfs_lookup_internal((char *) (buf + FS_NAME_MAXLEN),
                    size - FS_NAME_MAXLEN, &mp, NULL);
                if (rc != EOK) {
                        /*
                         * The lookup failed for some reason.
                         */
                        futex_up(&unlink_futex);
                        futex_up(&rootfs_futex);
                        vfs_node_put(mr_node);  /* failed -> drop reference */
                        free(buf);
                        ipc_answer_0(rid, rc);
                        return;
                }
                mp_node = vfs_node_get(&mp);
                if (!mp_node) {
                        futex_up(&unlink_futex);
                        futex_up(&rootfs_futex);
                        vfs_node_put(mr_node);  /* failed -> drop reference */
                        free(buf);
                        ipc_answer_0(rid, ENOMEM);
                        return;
                }
                /*
                 * Now we hold a reference to mp_node.
                 * It will be dropped upon the corresponding VFS_UNMOUNT.
                 * This prevents the mount point from being deleted.
                 */
                futex_up(&unlink_futex);
        } else {
                /*
                 * We still don't have the root file system mounted.
                 */
                if ((size - FS_NAME_MAXLEN == strlen("/")) &&
                    (buf[FS_NAME_MAXLEN] == '/')) {
                        /*
                         * For this simple, but important case, we are done.
                         */
                        rootfs = mounted_root;
                        futex_up(&rootfs_futex);
                        free(buf);
                        ipc_answer_0(rid, EOK);
                        return;
                } else {
                        /*
                         * We can't resolve this without the root filesystem
                         * being mounted first.
                         */
                        futex_up(&rootfs_futex);
                        free(buf);
                        vfs_node_put(mr_node);  /* failed -> drop reference */
                        ipc_answer_0(rid, ENOENT);
                        return;
                }
        }
        futex_up(&rootfs_futex);
        
        free(buf);      /* The buffer is not needed anymore. */
        
        /*
         * At this point, we have all necessary pieces: file system and device
         * handles, and we know the mount point VFS node and also the root node
         * of the file system being mounted.
         */

        int phone = vfs_grab_phone(mp.fs_handle);
        /* Later we can use ARG3 to pass mode/flags. */
        aid_t req1 = async_send_3(phone, VFS_MOUNT, (ipcarg_t) mp.dev_handle,
            (ipcarg_t) mp.index, 0, NULL);
        /* The second call uses the same method. */
        aid_t req2 = async_send_3(phone, VFS_MOUNT,
            (ipcarg_t) mounted_root.fs_handle,
            (ipcarg_t) mounted_root.dev_handle, (ipcarg_t) mounted_root.index,
            NULL);
        vfs_release_phone(phone);

        ipcarg_t rc1;
        ipcarg_t rc2;
        async_wait_for(req1, &rc1);
        async_wait_for(req2, &rc2);

        if ((rc1 != EOK) || (rc2 != EOK)) {
                /* Mount failed, drop references to mr_node and mp_node. */
                vfs_node_put(mr_node);
                if (mp_node)
                        vfs_node_put(mp_node);
        }
        
        if (rc2 == EOK)
                ipc_answer_0(rid, rc1);
        else if (rc1 == EOK)
                ipc_answer_0(rid, rc2);
        else
                ipc_answer_0(rid, rc1);
}

/**
 * @}
 */