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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] wating for backend changes (was Re: [PATCH v3 4/4] libxl: add support for vscsi)
How is new code supposed to wait for backend changes?
Right now there are two APIs for that:
- libxl__wait_for_backend loops for a while until it returns an error.
- libxl__ev_devstate_wait registers a watch and a timer.
In case of pvscsi there are three variants:
- new, can use libxl__wait_device_connection
- reconfigure, can use both of the above
- remove, may use DEFINE_DEVICE_REMOVE and its
libxl__initiate_device_remove
The reconfigure case has to wait for various states, depending on the
state before the reconfiguration.
The pci code in libxl uses just libxl__wait_for_backend. Looking through
the history it seems the function was added just for pci. Is it a
deprecated function, should callers get converted to
libxl__ev_devstate_wait?
Olaf
On Fri, Mar 06, Olaf Hering wrote:
> +void libxl__device_vscsi_add(libxl__egc *egc, uint32_t domid,
> + libxl_device_vscsi *vscsi,
> + libxl__ao_device *aodev)
> +{
> + STATE_AO_GC(aodev->ao);
> + libxl_ctx *ctx = libxl__gc_owner(gc);
> + flexarray_t *front;
> + flexarray_t *back;
> + libxl__device *device;
> + char *be_path;
> + unsigned int be_dirs = 0, rc, i;
> +
> + if (vscsi->devid == -1) {
> + rc = ERROR_FAIL;
> + goto out;
> + }
> +
> + /* Prealloc key+value: 4 toplevel + 4 per device */
> + i = 2 * (4 + (4 * vscsi->num_vscsi_devs));
> + back = flexarray_make(gc, i, 1);
> + front = flexarray_make(gc, 2 * 2, 1);
> +
> + GCNEW(device);
> + rc = libxl__device_from_vscsi(gc, domid, vscsi, device);
> + if ( rc != 0 ) goto out;
> +
> + /* Check if backend device path is already present */
> + be_path = libxl__device_backend_path(gc, device);
> + if (!libxl__xs_directory(gc, XBT_NULL, be_path, &be_dirs) || !be_dirs) {
> + /* backend does not exist, create a new one */
> + flexarray_append_pair(back, "frontend-id", GCSPRINTF("%d", domid));
> + flexarray_append_pair(back, "online", "1");
> + flexarray_append_pair(back, "state", "1");
> + flexarray_append_pair(back, "feature-host", GCSPRINTF("%d",
> !!vscsi->feature_host));
> +
> + flexarray_append_pair(front, "backend-id", GCSPRINTF("%d",
> vscsi->backend_domid));
> + flexarray_append_pair(front, "state", "1");
> + }
> +
> + for (i = 0; i < vscsi->num_vscsi_devs; i++) {
> + libxl_vscsi_dev *v = vscsi->vscsi_devs + i;
> + /* Trigger removal, otherwise create new device */
> + if (be_dirs) {
> + unsigned int nb = 0;
> + /* Preserve existing device */
> + if (libxl__xs_directory(gc, XBT_NULL,
> GCSPRINTF("%s/vscsi-devs/dev-%u", be_path, v->vscsi_dev_id), &nb) && nb) {
> + /* Trigger device removal by forwarding state to
> XenbusStateClosing */
> + if (v->remove)
> + flexarray_append_pair(back,
> GCSPRINTF("vscsi-devs/dev-%u/state", v->vscsi_dev_id), "5");
> + continue;
> + }
> + }
> + flexarray_append_pair(back, GCSPRINTF("vscsi-devs/dev-%u/p-devname",
> v->vscsi_dev_id), v->p_devname);
> + switch (v->pdev_type) {
> + case LIBXL_VSCSI_PDEV_TYPE_WWN:
> + flexarray_append_pair(back,
> + GCSPRINTF("vscsi-devs/dev-%u/p-dev",
> v->vscsi_dev_id),
> + v->p_devname);
> + break;
> + case LIBXL_VSCSI_PDEV_TYPE_DEV:
> + case LIBXL_VSCSI_PDEV_TYPE_HCTL:
> + flexarray_append_pair(back,
> + GCSPRINTF("vscsi-devs/dev-%u/p-dev",
> v->vscsi_dev_id),
> + GCSPRINTF("%u:%u:%u:%u", v->pdev.hst,
> v->pdev.chn, v->pdev.tgt, v->pdev.lun));
> + break;
> + case LIBXL_VSCSI_PDEV_TYPE_INVALID:
> + default:
> + rc = ERROR_FAIL;
> + goto out;
> + }
> + flexarray_append_pair(back, GCSPRINTF("vscsi-devs/dev-%u/v-dev",
> v->vscsi_dev_id),
> + GCSPRINTF("%u:%u:%u:%u", v->vdev.hst,
> v->vdev.chn, v->vdev.tgt, v->vdev.lun));
> + flexarray_append_pair(back, GCSPRINTF("vscsi-devs/dev-%u/state",
> v->vscsi_dev_id), "1");
> + }
> +
> + aodev->dev = device;
> + /* Either create new host or reconfigure existing host */
> + if (be_dirs == 0) {
> + libxl__device_generic_add(gc, XBT_NULL, device,
> + libxl__xs_kvs_of_flexarray(gc, back,
> back->count),
> + libxl__xs_kvs_of_flexarray(gc, front,
> front->count),
> + NULL);
> + aodev->action = LIBXL__DEVICE_ACTION_ADD;
> + libxl__wait_device_connection(egc, aodev);
> + rc = 0;
> + /* Done with new host */
> + goto out;
> + }
> +
> + /* Only new devices, write them and do vscsi host reconfiguration */
> + xs_transaction_t t;
> +retry_transaction:
> + t = xs_transaction_start(ctx->xsh);
> + libxl__xs_writev(gc, t, be_path,
> + libxl__xs_kvs_of_flexarray(gc, back, back->count));
> + xs_write(ctx->xsh, t, GCSPRINTF("%s/state", be_path), "7", 2);
> + if (!xs_transaction_end(ctx->xsh, t, 0)) {
> + if (errno == EAGAIN)
> + goto retry_transaction;
> + LOGE(ERROR, "xs transaction failed");
> + rc = ERROR_FAIL;
> + goto out;
> + }
> + libxl__wait_for_backend(gc, be_path, "4");
> +
> +retry_transaction2:
> + t = xs_transaction_start(ctx->xsh);
> + for (i = 0; i < vscsi->num_vscsi_devs; i++) {
> + libxl_vscsi_dev *v = vscsi->vscsi_devs + i;
> + if (v->remove) {
> + char *path, *val;
> + path = GCSPRINTF("%s/vscsi-devs/dev-%u/state", be_path,
> v->vscsi_dev_id);
> + val = libxl__xs_read(gc, t, path);
> + if (val && strcmp(val, "6") == 0) {
> + path = GCSPRINTF("%s/vscsi-devs/dev-%u/state", be_path,
> v->vscsi_dev_id);
> + xs_rm(ctx->xsh, t, path);
> + path = GCSPRINTF("%s/vscsi-devs/dev-%u/p-devname", be_path,
> v->vscsi_dev_id);
> + xs_rm(ctx->xsh, t, path);
> + path = GCSPRINTF("%s/vscsi-devs/dev-%u/p-dev", be_path,
> v->vscsi_dev_id);
> + xs_rm(ctx->xsh, t, path);
> + path = GCSPRINTF("%s/vscsi-devs/dev-%u/v-dev", be_path,
> v->vscsi_dev_id);
> + xs_rm(ctx->xsh, t, path);
> + path = GCSPRINTF("%s/vscsi-devs/dev-%u", be_path,
> v->vscsi_dev_id);
> + xs_rm(ctx->xsh, t, path);
> + } else {
> + LOGE(ERROR, "%s: %s has %s, expected 6", __func__, path,
> val);
> + }
> + }
> + }
> +
> + if (!xs_transaction_end(ctx->xsh, t, 0)) {
> + if (errno == EAGAIN)
> + goto retry_transaction2;
> + LOGE(ERROR, "xs transaction failed");
> + rc = ERROR_FAIL;
> + goto out;
> + }
> + /* As we are not adding new device, skip waiting for it */
> + libxl__ao_complete(egc, aodev->ao, 0);
> +
> + rc = 0;
> +out:
> + aodev->rc = rc;
> + if(rc) aodev->callback(egc, aodev);
> + return;
> +}
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