Example #1
0
int create_instance_backing (ncInstance * instance)
{
    int ret = ERROR;
    virtualMachine * vm = &(instance->params);
    artifact * sentinel = NULL;

    // ensure instance directory exists
    set_path (instance->instancePath,    sizeof (instance->instancePath),    instance, NULL);
    if (ensure_directories_exist (instance->instancePath, 0, NULL, "root", BACKING_DIRECTORY_PERM) == -1)
        goto out;

    // set various instance-directory-relative paths in the instance struct
    set_path (instance->xmlFilePath,     sizeof (instance->xmlFilePath),     instance, "instance.xml");
    set_path (instance->libvirtFilePath, sizeof (instance->libvirtFilePath), instance, "libvirt.xml");
    set_path (instance->consoleFilePath, sizeof (instance->consoleFilePath), instance, "console.log");
    if (strstr (instance->platform, "windows")) {
        // generate the floppy file for windows instances
        if (makeWindowsFloppy (nc_state.home, instance->instancePath, instance->keyName, instance->instanceId)) {
            logprintfl (EUCAERROR, "[%s] error: could not create windows bootup script floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path (instance->floppyFilePath, sizeof (instance->floppyFilePath), instance, "floppy");
        }
    }
    
    char work_prefix [1024]; // {userId}/{instanceId}
    set_id (instance, NULL, work_prefix, sizeof (work_prefix));
    
    // compute tree of dependencies
    sentinel = vbr_alloc_tree (vm, // the struct containing the VBR
                               FALSE, // for Xen and KVM we do not need to make disk bootable
                               TRUE, // make working copy of runtime-modifiable files
                               (instance->do_inject_key)?(instance->keyName):(NULL), // the SSH key
                               instance->instanceId); // ID is for logging
    if (sentinel == NULL) {
        logprintfl (EUCAERROR, "[%s] error: failed to prepare backing for instance\n", instance->instanceId);
        goto out;
    }

    sem_p (disk_sem);
    // download/create/combine the dependencies
    int rc = art_implement_tree (sentinel, work_bs, cache_bs, work_prefix, INSTANCE_PREP_TIMEOUT_USEC);
    sem_v (disk_sem);

    if (rc != OK) {
        logprintfl (EUCAERROR, "[%s] error: failed to implement backing for instance\n", instance->instanceId);
        goto out;
    }

    if (save_instance_struct (instance)) // update instance checkpoint now that the struct got updated
        goto out;

    ret = OK;
 out:
    if (sentinel)
        art_free (sentinel);
    return ret;
}
Example #2
0
//!
//! Main entry point of the application
//!
//! @param[in] argc the number of parameter passed on the command line
//! @param[in] argv the list of arguments
//!
//! @return EUCA_OK on success or EUCA_ERROR on failure.
//!
int main(int argc, char *argv[])
{
    int i = 0;
    int ret = EUCA_OK;
    int nparams = 0;
    int ncmds = 0;
    char *eq = NULL;
    char *key = NULL;
    char *val = NULL;
    char euca_root[] = "";
    char argv_str[4096] = "";
    char *cmd_name = NULL;
    char pid_file[EUCA_MAX_PATH] = "";
    FILE *fp = NULL;
    pid_t pid = 0;
    artifact *root = NULL;
    blobstore *work_bs = NULL;
    blobstore *cache_bs = NULL;
    imager_param *cmd_params = NULL;

    log_fp_set(stderr); // imager logs to stderr so image data can be piped to stdout
    set_debug(print_debug);

    // initialize globals
    artifacts_map = map_create(10);

    // use $EUCALYPTUS env var if available
    euca_home = getenv(EUCALYPTUS_ENV_VAR_NAME);
    if (!euca_home) {
        euca_home = euca_root;
    }
    // save the command line into a buffer so it's easier to rerun it by hand
    argv_str[0] = '\0';
    for (i = 0; i < argc; i++) {
        strncat(argv_str, "\"", sizeof(argv_str) - strlen(argv_str) - 1);
        strncat(argv_str, argv[i], sizeof(argv_str) - strlen(argv_str) - 1);
        strncat(argv_str, "\" ", sizeof(argv_str) - strlen(argv_str) - 1);
    }

    // initialize dependencies
    if (vmdk_init() == EUCA_OK) {
        vddk_available = TRUE;
    }

    // parse command-line parameters
    while (*(++argv)) {
        eq = strstr(*argv, "=");       // all params have '='s
        if (eq == NULL) {              // it's a command
            // process previous command, if any
            if (validate_cmd(ncmds, cmd_name, cmd_params, *argv) != NULL)
                ncmds++;               // increment only if there was a previous command

            if (ncmds + 1 > MAX_REQS)
                err("too many commands (max is %d)", MAX_REQS);

            cmd_name = *argv;
            cmd_params = NULL;
            nparams = 0;
        } else {                       // this is a parameter
            if (strlen(eq) == 1)
                usage("parameters must have non-empty values");
            *eq = '\0';                // split key from value
            if (strlen(*argv) == 1)
                usage("parameters must have non-empty names");

            key = *argv;
            val = eq + 1;
            if (key == NULL || val == NULL)
                usage("syntax error in parameters");

            if (key[0] == '-')
                key++;                 // skip '-' if any

            if (key[0] == '-')
                key++;                 // skip second '-' if any

            if (cmd_name == NULL) {    // without a preceding command => global parameter
                set_global_parameter(key, val);
                continue;
            }

            if (cmd_params == NULL) {
                cmd_params = calloc(MAX_PARAMS + 1, sizeof(imager_param));  // +1 for terminating NULL
                if (!cmd_params)
                    err("calloc failed");
            }

            if (nparams + 1 > MAX_PARAMS)
                err("too many parameters (max is %d)", MAX_PARAMS);
            cmd_params[nparams].key = key;
            cmd_params[nparams].val = val;
            nparams++;
        }
    }

    if (validate_cmd(ncmds, cmd_name, cmd_params, *argv) != NULL)   // validate last command
        ncmds++;

    LOGINFO("verified all parameters for %d command(s)\n", ncmds);
    if (print_argv) {
        LOGDEBUG("argv[]: %s\n", argv_str);
    }
    // record PID, which may be used by VB to kill the imager process (e.g., in cancelBundling)
    pid = getpid();
    sprintf(pid_file, "%s/imager.pid", get_work_dir());
    if ((fp = fopen(pid_file, "w")) == NULL) {
        err("could not create pid file");
    } else {
        fprintf(fp, "%d", pid);
        fclose(fp);
    }

    // invoke the requirements checkers in the same order as on command line,
    // constructing the artifact tree originating at 'root'
    for (i = 0; i < ncmds; i++) {
        if (reqs[i].cmd->requirements != NULL) {
            art_set_instanceId(reqs[i].cmd->name);  // for logging
            if ((root = reqs[i].cmd->requirements(&reqs[i], root)) == NULL) // pass results of earlier checkers to later checkers
                err("failed while verifying requirements");
        }
    }

    // it is OK for root to be NULL at this point

    // see if work blobstore will be needed at any stage
    // and open or create the work blobstore
    if (root && tree_uses_blobstore(root)) {
        // set the function that will catch blobstore errors
        blobstore_set_error_function(&bs_errors);

        if (ensure_directories_exist(get_work_dir(), 0, NULL, NULL, BLOBSTORE_DIRECTORY_PERM) == -1)
            err("failed to open or create work directory %s", get_work_dir());

        work_bs = blobstore_open(get_work_dir(), get_work_limit() / 512, BLOBSTORE_FLAG_CREAT, BLOBSTORE_FORMAT_FILES, BLOBSTORE_REVOCATION_NONE, BLOBSTORE_SNAPSHOT_ANY);
        if (work_bs == NULL) {
            err("failed to open work blobstore: %s", blobstore_get_error_str(blobstore_get_error()));
        }
        // no point in fscking the work blobstore as it was just created
    }
    // see if cache blobstore will be needed at any stage
    if (root && tree_uses_cache(root)) {
        if (ensure_directories_exist(get_cache_dir(), 0, NULL, NULL, BLOBSTORE_DIRECTORY_PERM) == -1)
            err("failed to open or create cache directory %s", get_cache_dir());
        cache_bs = blobstore_open(get_cache_dir(), get_cache_limit() / 512, BLOBSTORE_FLAG_CREAT, BLOBSTORE_FORMAT_DIRECTORY, BLOBSTORE_REVOCATION_LRU, BLOBSTORE_SNAPSHOT_ANY);
        if (cache_bs == NULL) {
            blobstore_close(work_bs);
            err("failed to open cache blobstore: %s\n", blobstore_get_error_str(blobstore_get_error()));
        }

        if (blobstore_fsck(cache_bs, NULL)) //! @TODO: verify checksums?
            err("cache blobstore failed integrity check: %s", blobstore_get_error_str(blobstore_get_error()));

        if (stat_blobstore(get_cache_dir(), cache_bs))
            err("blobstore is unreadable");
    }
    // implement the artifact tree
    ret = EUCA_OK;
    if (root) {
        art_set_instanceId("imager");  // for logging
        ret = art_implement_tree(root, work_bs, cache_bs, NULL, INSTANCE_PREP_TIMEOUT_USEC);    // do all the work!
    }
    // invoke the cleaners for each command to tidy up disk space and memory allocations
    for (i = 0; i < ncmds; i++) {
        if (reqs[i].cmd->cleanup != NULL) {
            art_set_instanceId(reqs[i].cmd->name);  // for logging
            reqs[i].cmd->cleanup(&reqs[i], (i == (ncmds - 1)) ? (TRUE) : (FALSE));
        }
    }

    // free the artifact tree
    if (root) {
        if (tree_uses_blobstore(root)) {
            if (blobstore_fsck(work_bs, stale_blob_examiner)) { // will remove all blobs
                LOGWARN("failed to clean up work space: %s\n", blobstore_get_error_str(blobstore_get_error()));
            }
        }
        art_free(root);
    }
    clean_work_dir(work_bs);

    // indicate completion
    LOGINFO("imager done (exit code=%d)\n", ret);

    exit(ret);
}
//!
//! Implement the backing store for a given instance
//!
//! @param[in] instance pointer to the instance
//! @param[in] is_migration_dest
//!
//! @return EUCA_OK on success or EUCA_ERROR on failure
//!
//! @pre The instance parameter must not be NULL.
//!
//! @post
//!
int create_instance_backing(ncInstance * instance, boolean is_migration_dest)
{
    int rc = 0;
    int ret = EUCA_ERROR;
    virtualMachine *vm = &(instance->params);
    artifact *sentinel = NULL;
    char work_prefix[1024] = { 0 };    // {userId}/{instanceId}

    // set various instance-directory-relative paths in the instance struct
    set_instance_paths(instance);

    // ensure instance directory exists
    if (ensure_directories_exist(instance->instancePath, 0, NULL, "root", BACKING_DIRECTORY_PERM) == -1)
        goto out;

    if (strstr(instance->platform, "windows")) {
        // generate the floppy file for windows instances
        if (makeWindowsFloppy(nc_state.home, instance->instancePath, instance->keyName, instance->instanceId)) {
            LOGERROR("[%s] could not create windows bootup script floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path(instance->floppyFilePath, sizeof(instance->floppyFilePath), instance, "floppy");
        }
    } else if (strlen(instance->instancePk) > 0) {  // TODO: credential floppy is limited to Linux instances ATM
        LOGDEBUG("[%s] creating floppy for instance credential\n", instance->instanceId);
        if (make_credential_floppy(nc_state.home, instance)) {
            LOGERROR("[%s] could not create credential floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path(instance->floppyFilePath, sizeof(instance->floppyFilePath), instance, "floppy");
        }
    }

    set_id(instance, NULL, work_prefix, sizeof(work_prefix));

    // if this looks like a partition m1.small image, make it a bootable disk
    virtualMachine *vm2 = NULL;
    LOGDEBUG("vm->virtualBootRecordLen=%d\n", vm->virtualBootRecordLen);
    if (vm->virtualBootRecordLen == 5) {    // TODO: make this check more robust

        // as an experiment, construct a new VBR, without swap and ephemeral
        virtualMachine vm_copy;
        vm2 = &vm_copy;
        memcpy(vm2, vm, sizeof(virtualMachine));
        bzero(vm2->virtualBootRecord, EUCA_MAX_VBRS * sizeof(virtualBootRecord));
        vm2->virtualBootRecordLen = 0;

        virtualBootRecord *emi_vbr = NULL;
        for (int i = 0; i < EUCA_MAX_VBRS && i < vm->virtualBootRecordLen; i++) {
            virtualBootRecord *vbr = &(vm->virtualBootRecord[i]);
            if (vbr->type != NC_RESOURCE_KERNEL && vbr->type != NC_RESOURCE_RAMDISK && vbr->type != NC_RESOURCE_IMAGE)
                continue;
            if (vbr->type == NC_RESOURCE_IMAGE)
                emi_vbr = vbr;
            memcpy(vm2->virtualBootRecord + (vm2->virtualBootRecordLen++), vbr, sizeof(virtualBootRecord));
        }

        if (emi_vbr == NULL) {
            LOGERROR("[%s] failed to find EMI among VBR entries\n", instance->instanceId);
            goto out;
        }

        if (vbr_add_ascii("boot:none:104857600:ext3:sda2:none", vm2) != EUCA_OK) {
            LOGERROR("[%s] could not add a boot partition VBR entry\n", instance->instanceId);
            goto out;
        }
        if (vbr_parse(vm2, NULL) != EUCA_OK) {
            LOGERROR("[%s] could not parse the boot partition VBR entry\n", instance->instanceId);
            goto out;
        }
        // compute tree of dependencies
        sentinel = vbr_alloc_tree(vm2, // the struct containing the VBR
                                  TRUE, // we always make the disk bootable, for consistency
                                  TRUE, // make working copy of runtime-modifiable files
                                  is_migration_dest,    // tree of an instance on the migration destination
                                  (instance->do_inject_key) ? (instance->keyName) : (NULL), // the SSH key
                                  instance->instanceId);    // ID is for logging
        if (sentinel == NULL) {
            LOGERROR("[%s] failed to prepare backing for instance\n", instance->instanceId);
            goto out;
        }

        LOGDEBUG("disk size prior to tree implementation is = %lld\n", sentinel->deps[0]->size_bytes);
        long long right_disk_size = sentinel->deps[0]->size_bytes;

        sem_p(disk_sem);
        {
            // download/create/combine the dependencies
            rc = art_implement_tree(sentinel, work_bs, cache_bs, work_prefix, INSTANCE_PREP_TIMEOUT_USEC);
        }
        sem_v(disk_sem);

        if (rc != EUCA_OK) {
            LOGERROR("[%s] failed to implement backing for instance\n", instance->instanceId);
            goto out;
        }

        LOGDEBUG("[%s] created the initial bootable disk\n", instance->instanceId);

        /* option A starts */
        assert(emi_vbr);
        assert(sentinel->deps[0]);
        strcpy(emi_vbr->guestDeviceName, "sda");    // switch 'sda1' to 'sda' now that we've built the disk
        //emi_vbr->sizeBytes = sentinel->deps[0]->size_bytes; // update the size to match the disk
        emi_vbr->sizeBytes = right_disk_size;   // this is bad...
        LOGDEBUG("at boot disk creation time emi_vbr->sizeBytes = %lld\n", emi_vbr->sizeBytes);
        euca_strncpy(emi_vbr->id, sentinel->deps[0]->id, SMALL_CHAR_BUFFER_SIZE);   // change to the ID of the disk
        if (vbr_parse(vm, NULL) != EUCA_OK) {
            LOGERROR("[%s] could not parse the boot partition VBR entry\n", instance->instanceId);
            goto out;
        }
        emi_vbr->locationType = NC_LOCATION_NONE;   // i.e., it should already exist

        art_free(sentinel);
        /* option A end */

        /* option B starts *
           memcpy(vm, vm2, sizeof(virtualMachine));
           if (save_instance_struct(instance)) // update instance checkpoint now that the struct got updated
           goto out;
           ret = EUCA_OK;
           goto out;
           * option B ends */
    }
    // compute tree of dependencies
    sentinel = vbr_alloc_tree(vm,      // the struct containing the VBR
                              FALSE,   // if image had to be made bootable, that was done above
                              TRUE,    // make working copy of runtime-modifiable files
                              is_migration_dest,    // tree of an instance on the migration destination
                              (instance->do_inject_key) ? (instance->keyName) : (NULL), // the SSH key
                              instance->instanceId);    // ID is for logging
    if (sentinel == NULL) {
        LOGERROR("[%s] failed to prepare extended backing for instance\n", instance->instanceId);
        goto out;
    }

    sem_p(disk_sem);
    {
        // download/create/combine the dependencies
        rc = art_implement_tree(sentinel, work_bs, cache_bs, work_prefix, INSTANCE_PREP_TIMEOUT_USEC);
    }
    sem_v(disk_sem);

    if (rc != EUCA_OK) {
        LOGERROR("[%s] failed to implement backing for instance\n", instance->instanceId);
        goto out;
    }

    if (save_instance_struct(instance)) // update instance checkpoint now that the struct got updated
        goto out;

    ret = EUCA_OK;

out:
    if (sentinel)
        art_free(sentinel);
    return (ret);
}
Example #4
0
//!
//! Implement the backing store for a given instance
//!
//! @param[in] instance pointer to the instance
//! @param[in] is_migration_dest
//!
//! @return EUCA_OK on success or EUCA_ERROR on failure
//!
//! @pre The instance parameter must not be NULL.
//!
//! @post
//!
int create_instance_backing(ncInstance * instance, boolean is_migration_dest)
{
    int rc = 0;
    int ret = EUCA_ERROR;
    virtualMachine *vm = &(instance->params);
    artifact *sentinel = NULL;
    char work_prefix[1024] = { 0 };    // {userId}/{instanceId}
    char base_path[EUCA_MAX_PATH];
    char user_dir_path[EUCA_MAX_PATH];

    // set various instance-directory-relative paths in the instance struct
    set_instance_paths(instance);

    set_path(base_path, sizeof(base_path), NULL, NULL);
    snprintf(user_dir_path, sizeof(user_dir_path), "%s/%s", base_path, instance->userId);
    // create backing directory
    if ((check_path(user_dir_path) == 1) && (mkdir(user_dir_path, INSTANCE_DIRECTORY_PERM) == -1)) {
        LOGERROR("[%s] could not create backing directory %s\n", instance->instanceId, user_dir_path);
        goto out;
    }
    if (mkdir(instance->instancePath, INSTANCE_DIRECTORY_PERM) == -1) {
        LOGERROR("[%s] could not create backing directory %s\n", instance->instanceId, instance->instancePath);
        goto out;
    }

    if (strstr(instance->platform, "windows")) {
        // generate the floppy file for windows instances
        if (makeWindowsFloppy(nc_state.home, instance->instancePath, instance->keyName, instance->instanceId)) {
            LOGERROR("[%s] could not create windows bootup script floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path(instance->floppyFilePath, sizeof(instance->floppyFilePath), instance, "floppy");
            instance->hasFloppy = TRUE;
        }
    } else if (instance->credential && strlen(instance->credential)) {
        LOGDEBUG("[%s] creating floppy for instance credential\n", instance->instanceId);
        if (make_credential_floppy(nc_state.home, instance->instancePath, instance->credential)) {
            LOGERROR("[%s] could not create credential floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path(instance->floppyFilePath, sizeof(instance->floppyFilePath), instance, "floppy");
            instance->hasFloppy = TRUE;
        }
    } else if(instance->hasFloppy && is_migration_dest) {
        LOGDEBUG("[%s] creating blank instance credential floppy\n", instance->instanceId);
        char dest_path[1024] = "";
        int fd = 0;
        snprintf(dest_path, 1024, "%s/floppy", instance->instancePath);
        if ((fd = open(dest_path, O_CREAT | O_TRUNC | O_RDWR, 0700)) < 0) {
           LOGERROR("[%s] failed to create fake floppy\n", instance->instanceId);
           goto out;
        } else {
           lseek(fd, 1024*2048-1, SEEK_SET);
           write(fd, "\n", 1);
        }
        close(fd);
    } else {
        instance->hasFloppy = FALSE;
    }

    set_id(instance, NULL, work_prefix, sizeof(work_prefix));

    // compute tree of dependencies
    sentinel = vbr_alloc_tree(vm,      // the struct containing the VBR
                              TRUE,    // make working copy of runtime-modifiable files
                              is_migration_dest,    // tree of an instance on the migration destination
                              (instance->do_inject_key) ? (instance->keyName) : (NULL), // the SSH key
                              &(instance->bail_flag),   // flag indicating that provisioning should bail
                              instance->instanceId);    // ID is for logging
    if (sentinel == NULL) {
        LOGERROR("[%s] failed to prepare extended backing for instance\n", instance->instanceId);
        goto out;
    }

    sem_p(disk_sem);
    {
        // download/create/combine the dependencies
        rc = art_implement_tree(sentinel, work_bs, cache_bs, work_prefix, INSTANCE_PREP_TIMEOUT_USEC);
    }
    sem_v(disk_sem);

    if (rc != EUCA_OK) {
        LOGERROR("[%s] failed to implement backing for instance\n", instance->instanceId);
        goto out;
    }
    // copy EBS entries from VBR[] to volumes[]
    for (int i = 0; ((i < EUCA_MAX_VBRS) && (i < instance->params.virtualBootRecordLen)); i++) {
        virtualBootRecord *vbr = &(instance->params.virtualBootRecord[i]);
        if (vbr->locationType == NC_LOCATION_SC) {
            char *volumeId = vbr->id;  // id is 'emi-XXXX', replace it with 'vol-XXXX'
            ebs_volume_data *vol_data = NULL;
            if (deserialize_volume(vbr->resourceLocation, &vol_data) == 0) {
                volumeId = vol_data->volumeId;
            }
            if (save_volume(instance, volumeId, vbr->resourceLocation,  // attachmentToken
                            vbr->preparedResourceLocation,  // connect_string
                            vbr->guestDeviceName, VOL_STATE_ATTACHED, vbr->backingPath) == NULL) {  // the XML
                LOGERROR("[%s] failed to add record for volume %s\n", instance->instanceId, volumeId);
            }
            EUCA_FREE(vol_data);
        }
    }

    if (save_instance_struct(instance)) // update instance checkpoint now that the struct got updated
        goto out;

    ret = EUCA_OK;

out:
    if (sentinel)
        art_free(sentinel);
    return (ret);
}
Example #5
0
//!
//! Implement the backing store for a given instance
//!
//! @param[in] instance pointer to the instance
//! @param[in] is_migration_dest
//!
//! @return EUCA_OK on success or EUCA_ERROR on failure
//!
//! @pre The instance parameter must not be NULL.
//!
//! @post
//!
int create_instance_backing(ncInstance * instance, boolean is_migration_dest)
{
    int rc = 0;
    int ret = EUCA_ERROR;
    virtualMachine *vm = &(instance->params);
    artifact *sentinel = NULL;
    char work_prefix[1024] = { 0 };    // {userId}/{instanceId}

    // set various instance-directory-relative paths in the instance struct
    set_instance_paths(instance);

    // ensure instance directory exists
    if (ensure_directories_exist(instance->instancePath, 0, NULL, "root", BACKING_DIRECTORY_PERM) == -1)
        goto out;

    if (strstr(instance->platform, "windows")) {
        // generate the floppy file for windows instances
        if (makeWindowsFloppy(nc_state.home, instance->instancePath, instance->keyName, instance->instanceId)) {
            LOGERROR("[%s] could not create windows bootup script floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path(instance->floppyFilePath, sizeof(instance->floppyFilePath), instance, "floppy");
        }
    }else if (instance->instancePk != NULL && strlen(instance->instancePk) > 0) {  // TODO: credential floppy is limited to Linux instances ATM
        LOGDEBUG("[%s] creating floppy for instance credential\n", instance->instanceId);
        if (make_credential_floppy(nc_state.home, instance)) {
            LOGERROR("[%s] could not create credential floppy\n", instance->instanceId);
            goto out;
        } else {
            set_path(instance->floppyFilePath, sizeof(instance->floppyFilePath), instance, "floppy");
        }
    }

    set_id(instance, NULL, work_prefix, sizeof(work_prefix));

    // compute tree of dependencies
    sentinel = vbr_alloc_tree(vm,      // the struct containing the VBR
                              FALSE,   // for Xen and KVM we do not need to make disk bootable
                              TRUE,    // make working copy of runtime-modifiable files
                              is_migration_dest,    // tree of an instance on the migration destination
                              (instance->do_inject_key) ? (instance->keyName) : (NULL), // the SSH key
                              instance->instanceId);    // ID is for logging
    if (sentinel == NULL) {
        LOGERROR("[%s] failed to prepare backing for instance\n", instance->instanceId);
        goto out;
    }

    sem_p(disk_sem);
    {
        // download/create/combine the dependencies
        rc = art_implement_tree(sentinel, work_bs, cache_bs, work_prefix, INSTANCE_PREP_TIMEOUT_USEC);
    }
    sem_v(disk_sem);

    if (rc != EUCA_OK) {
        LOGERROR("[%s] failed to implement backing for instance\n", instance->instanceId);
        goto out;
    }

    if (save_instance_struct(instance)) // update instance checkpoint now that the struct got updated
        goto out;

    ret = EUCA_OK;

out:
    if (sentinel)
        art_free(sentinel);
    return (ret);
}