1 /* 2 * Device operations for the pnfs nfs4 file layout driver. 3 * 4 * Copyright (c) 2014, Primary Data, Inc. All rights reserved. 5 * 6 * Tao Peng <bergwolf@primarydata.com> 7 */ 8 9 #include <linux/nfs_fs.h> 10 #include <linux/vmalloc.h> 11 #include <linux/module.h> 12 #include <linux/sunrpc/addr.h> 13 14 #include "../internal.h" 15 #include "../nfs4session.h" 16 #include "flexfilelayout.h" 17 18 #define NFSDBG_FACILITY NFSDBG_PNFS_LD 19 20 static unsigned int dataserver_timeo = NFS_DEF_TCP_RETRANS; 21 static unsigned int dataserver_retrans; 22 23 static bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg); 24 25 void nfs4_ff_layout_put_deviceid(struct nfs4_ff_layout_ds *mirror_ds) 26 { 27 if (!IS_ERR_OR_NULL(mirror_ds)) 28 nfs4_put_deviceid_node(&mirror_ds->id_node); 29 } 30 31 void nfs4_ff_layout_free_deviceid(struct nfs4_ff_layout_ds *mirror_ds) 32 { 33 nfs4_print_deviceid(&mirror_ds->id_node.deviceid); 34 nfs4_pnfs_ds_put(mirror_ds->ds); 35 kfree_rcu(mirror_ds, id_node.rcu); 36 } 37 38 /* Decode opaque device data and construct new_ds using it */ 39 struct nfs4_ff_layout_ds * 40 nfs4_ff_alloc_deviceid_node(struct nfs_server *server, struct pnfs_device *pdev, 41 gfp_t gfp_flags) 42 { 43 struct xdr_stream stream; 44 struct xdr_buf buf; 45 struct page *scratch; 46 struct list_head dsaddrs; 47 struct nfs4_pnfs_ds_addr *da; 48 struct nfs4_ff_layout_ds *new_ds = NULL; 49 struct nfs4_ff_ds_version *ds_versions = NULL; 50 u32 mp_count; 51 u32 version_count; 52 __be32 *p; 53 int i, ret = -ENOMEM; 54 55 /* set up xdr stream */ 56 scratch = alloc_page(gfp_flags); 57 if (!scratch) 58 goto out_err; 59 60 new_ds = kzalloc(sizeof(struct nfs4_ff_layout_ds), gfp_flags); 61 if (!new_ds) 62 goto out_scratch; 63 64 nfs4_init_deviceid_node(&new_ds->id_node, 65 server, 66 &pdev->dev_id); 67 INIT_LIST_HEAD(&dsaddrs); 68 69 xdr_init_decode_pages(&stream, &buf, pdev->pages, pdev->pglen); 70 xdr_set_scratch_buffer(&stream, page_address(scratch), PAGE_SIZE); 71 72 /* multipath count */ 73 p = xdr_inline_decode(&stream, 4); 74 if (unlikely(!p)) 75 goto out_err_drain_dsaddrs; 76 mp_count = be32_to_cpup(p); 77 dprintk("%s: multipath ds count %d\n", __func__, mp_count); 78 79 for (i = 0; i < mp_count; i++) { 80 /* multipath ds */ 81 da = nfs4_decode_mp_ds_addr(server->nfs_client->cl_net, 82 &stream, gfp_flags); 83 if (da) 84 list_add_tail(&da->da_node, &dsaddrs); 85 } 86 if (list_empty(&dsaddrs)) { 87 dprintk("%s: no suitable DS addresses found\n", 88 __func__); 89 ret = -ENOMEDIUM; 90 goto out_err_drain_dsaddrs; 91 } 92 93 /* version count */ 94 p = xdr_inline_decode(&stream, 4); 95 if (unlikely(!p)) 96 goto out_err_drain_dsaddrs; 97 version_count = be32_to_cpup(p); 98 dprintk("%s: version count %d\n", __func__, version_count); 99 100 ds_versions = kzalloc(version_count * sizeof(struct nfs4_ff_ds_version), 101 gfp_flags); 102 if (!ds_versions) 103 goto out_scratch; 104 105 for (i = 0; i < version_count; i++) { 106 /* 20 = version(4) + minor_version(4) + rsize(4) + wsize(4) + 107 * tightly_coupled(4) */ 108 p = xdr_inline_decode(&stream, 20); 109 if (unlikely(!p)) 110 goto out_err_drain_dsaddrs; 111 ds_versions[i].version = be32_to_cpup(p++); 112 ds_versions[i].minor_version = be32_to_cpup(p++); 113 ds_versions[i].rsize = nfs_block_size(be32_to_cpup(p++), NULL); 114 ds_versions[i].wsize = nfs_block_size(be32_to_cpup(p++), NULL); 115 ds_versions[i].tightly_coupled = be32_to_cpup(p); 116 117 if (ds_versions[i].rsize > NFS_MAX_FILE_IO_SIZE) 118 ds_versions[i].rsize = NFS_MAX_FILE_IO_SIZE; 119 if (ds_versions[i].wsize > NFS_MAX_FILE_IO_SIZE) 120 ds_versions[i].wsize = NFS_MAX_FILE_IO_SIZE; 121 122 if (ds_versions[i].version != 3 || ds_versions[i].minor_version != 0) { 123 dprintk("%s: [%d] unsupported ds version %d-%d\n", __func__, 124 i, ds_versions[i].version, 125 ds_versions[i].minor_version); 126 ret = -EPROTONOSUPPORT; 127 goto out_err_drain_dsaddrs; 128 } 129 130 dprintk("%s: [%d] vers %u minor_ver %u rsize %u wsize %u coupled %d\n", 131 __func__, i, ds_versions[i].version, 132 ds_versions[i].minor_version, 133 ds_versions[i].rsize, 134 ds_versions[i].wsize, 135 ds_versions[i].tightly_coupled); 136 } 137 138 new_ds->ds_versions = ds_versions; 139 new_ds->ds_versions_cnt = version_count; 140 141 new_ds->ds = nfs4_pnfs_ds_add(&dsaddrs, gfp_flags); 142 if (!new_ds->ds) 143 goto out_err_drain_dsaddrs; 144 145 /* If DS was already in cache, free ds addrs */ 146 while (!list_empty(&dsaddrs)) { 147 da = list_first_entry(&dsaddrs, 148 struct nfs4_pnfs_ds_addr, 149 da_node); 150 list_del_init(&da->da_node); 151 kfree(da->da_remotestr); 152 kfree(da); 153 } 154 155 __free_page(scratch); 156 return new_ds; 157 158 out_err_drain_dsaddrs: 159 while (!list_empty(&dsaddrs)) { 160 da = list_first_entry(&dsaddrs, struct nfs4_pnfs_ds_addr, 161 da_node); 162 list_del_init(&da->da_node); 163 kfree(da->da_remotestr); 164 kfree(da); 165 } 166 167 kfree(ds_versions); 168 out_scratch: 169 __free_page(scratch); 170 out_err: 171 kfree(new_ds); 172 173 dprintk("%s ERROR: returning %d\n", __func__, ret); 174 return NULL; 175 } 176 177 static void ff_layout_mark_devid_invalid(struct pnfs_layout_segment *lseg, 178 struct nfs4_deviceid_node *devid) 179 { 180 nfs4_delete_deviceid(devid->ld, devid->nfs_client, &devid->deviceid); 181 if (!ff_layout_has_available_ds(lseg)) 182 pnfs_error_mark_layout_for_return(lseg->pls_layout->plh_inode, 183 lseg); 184 } 185 186 static bool ff_layout_mirror_valid(struct pnfs_layout_segment *lseg, 187 struct nfs4_ff_layout_mirror *mirror, 188 bool create) 189 { 190 if (mirror == NULL || IS_ERR(mirror->mirror_ds)) 191 goto outerr; 192 if (mirror->mirror_ds == NULL) { 193 if (create) { 194 struct nfs4_deviceid_node *node; 195 struct pnfs_layout_hdr *lh = lseg->pls_layout; 196 struct nfs4_ff_layout_ds *mirror_ds = ERR_PTR(-ENODEV); 197 198 node = nfs4_find_get_deviceid(NFS_SERVER(lh->plh_inode), 199 &mirror->devid, lh->plh_lc_cred, 200 GFP_KERNEL); 201 if (node) 202 mirror_ds = FF_LAYOUT_MIRROR_DS(node); 203 204 /* check for race with another call to this function */ 205 if (cmpxchg(&mirror->mirror_ds, NULL, mirror_ds) && 206 mirror_ds != ERR_PTR(-ENODEV)) 207 nfs4_put_deviceid_node(node); 208 } else 209 goto outerr; 210 } 211 212 if (IS_ERR(mirror->mirror_ds)) 213 goto outerr; 214 215 if (mirror->mirror_ds->ds == NULL) { 216 struct nfs4_deviceid_node *devid; 217 devid = &mirror->mirror_ds->id_node; 218 ff_layout_mark_devid_invalid(lseg, devid); 219 return false; 220 } 221 return true; 222 outerr: 223 pnfs_error_mark_layout_for_return(lseg->pls_layout->plh_inode, lseg); 224 return false; 225 } 226 227 static void extend_ds_error(struct nfs4_ff_layout_ds_err *err, 228 u64 offset, u64 length) 229 { 230 u64 end; 231 232 end = max_t(u64, pnfs_end_offset(err->offset, err->length), 233 pnfs_end_offset(offset, length)); 234 err->offset = min_t(u64, err->offset, offset); 235 err->length = end - err->offset; 236 } 237 238 static int 239 ff_ds_error_match(const struct nfs4_ff_layout_ds_err *e1, 240 const struct nfs4_ff_layout_ds_err *e2) 241 { 242 int ret; 243 244 if (e1->opnum != e2->opnum) 245 return e1->opnum < e2->opnum ? -1 : 1; 246 if (e1->status != e2->status) 247 return e1->status < e2->status ? -1 : 1; 248 ret = memcmp(e1->stateid.data, e2->stateid.data, 249 sizeof(e1->stateid.data)); 250 if (ret != 0) 251 return ret; 252 ret = memcmp(&e1->deviceid, &e2->deviceid, sizeof(e1->deviceid)); 253 if (ret != 0) 254 return ret; 255 if (pnfs_end_offset(e1->offset, e1->length) < e2->offset) 256 return -1; 257 if (e1->offset > pnfs_end_offset(e2->offset, e2->length)) 258 return 1; 259 /* If ranges overlap or are contiguous, they are the same */ 260 return 0; 261 } 262 263 static void 264 ff_layout_add_ds_error_locked(struct nfs4_flexfile_layout *flo, 265 struct nfs4_ff_layout_ds_err *dserr) 266 { 267 struct nfs4_ff_layout_ds_err *err, *tmp; 268 struct list_head *head = &flo->error_list; 269 int match; 270 271 /* Do insertion sort w/ merges */ 272 list_for_each_entry_safe(err, tmp, &flo->error_list, list) { 273 match = ff_ds_error_match(err, dserr); 274 if (match < 0) 275 continue; 276 if (match > 0) { 277 /* Add entry "dserr" _before_ entry "err" */ 278 head = &err->list; 279 break; 280 } 281 /* Entries match, so merge "err" into "dserr" */ 282 extend_ds_error(dserr, err->offset, err->length); 283 list_replace(&err->list, &dserr->list); 284 kfree(err); 285 return; 286 } 287 288 list_add_tail(&dserr->list, head); 289 } 290 291 int ff_layout_track_ds_error(struct nfs4_flexfile_layout *flo, 292 struct nfs4_ff_layout_mirror *mirror, u64 offset, 293 u64 length, int status, enum nfs_opnum4 opnum, 294 gfp_t gfp_flags) 295 { 296 struct nfs4_ff_layout_ds_err *dserr; 297 298 if (status == 0) 299 return 0; 300 301 if (mirror->mirror_ds == NULL) 302 return -EINVAL; 303 304 dserr = kmalloc(sizeof(*dserr), gfp_flags); 305 if (!dserr) 306 return -ENOMEM; 307 308 INIT_LIST_HEAD(&dserr->list); 309 dserr->offset = offset; 310 dserr->length = length; 311 dserr->status = status; 312 dserr->opnum = opnum; 313 nfs4_stateid_copy(&dserr->stateid, &mirror->stateid); 314 memcpy(&dserr->deviceid, &mirror->mirror_ds->id_node.deviceid, 315 NFS4_DEVICEID4_SIZE); 316 317 spin_lock(&flo->generic_hdr.plh_inode->i_lock); 318 ff_layout_add_ds_error_locked(flo, dserr); 319 spin_unlock(&flo->generic_hdr.plh_inode->i_lock); 320 321 return 0; 322 } 323 324 static struct rpc_cred * 325 ff_layout_get_mirror_cred(struct nfs4_ff_layout_mirror *mirror, u32 iomode) 326 { 327 struct rpc_cred *cred, __rcu **pcred; 328 329 if (iomode == IOMODE_READ) 330 pcred = &mirror->ro_cred; 331 else 332 pcred = &mirror->rw_cred; 333 334 rcu_read_lock(); 335 do { 336 cred = rcu_dereference(*pcred); 337 if (!cred) 338 break; 339 340 cred = get_rpccred_rcu(cred); 341 } while(!cred); 342 rcu_read_unlock(); 343 return cred; 344 } 345 346 struct nfs_fh * 347 nfs4_ff_layout_select_ds_fh(struct pnfs_layout_segment *lseg, u32 mirror_idx) 348 { 349 struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, mirror_idx); 350 struct nfs_fh *fh = NULL; 351 352 if (!ff_layout_mirror_valid(lseg, mirror, false)) { 353 pr_err_ratelimited("NFS: %s: No data server for mirror offset index %d\n", 354 __func__, mirror_idx); 355 goto out; 356 } 357 358 /* FIXME: For now assume there is only 1 version available for the DS */ 359 fh = &mirror->fh_versions[0]; 360 out: 361 return fh; 362 } 363 364 /** 365 * nfs4_ff_layout_prepare_ds - prepare a DS connection for an RPC call 366 * @lseg: the layout segment we're operating on 367 * @ds_idx: index of the DS to use 368 * @fail_return: return layout on connect failure? 369 * 370 * Try to prepare a DS connection to accept an RPC call. This involves 371 * selecting a mirror to use and connecting the client to it if it's not 372 * already connected. 373 * 374 * Since we only need a single functioning mirror to satisfy a read, we don't 375 * want to return the layout if there is one. For writes though, any down 376 * mirror should result in a LAYOUTRETURN. @fail_return is how we distinguish 377 * between the two cases. 378 * 379 * Returns a pointer to a connected DS object on success or NULL on failure. 380 */ 381 struct nfs4_pnfs_ds * 382 nfs4_ff_layout_prepare_ds(struct pnfs_layout_segment *lseg, u32 ds_idx, 383 bool fail_return) 384 { 385 struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, ds_idx); 386 struct nfs4_pnfs_ds *ds = NULL; 387 struct nfs4_deviceid_node *devid; 388 struct inode *ino = lseg->pls_layout->plh_inode; 389 struct nfs_server *s = NFS_SERVER(ino); 390 unsigned int max_payload; 391 int status; 392 393 if (!ff_layout_mirror_valid(lseg, mirror, true)) { 394 pr_err_ratelimited("NFS: %s: No data server for offset index %d\n", 395 __func__, ds_idx); 396 goto out; 397 } 398 399 devid = &mirror->mirror_ds->id_node; 400 if (ff_layout_test_devid_unavailable(devid)) 401 goto out_fail; 402 403 ds = mirror->mirror_ds->ds; 404 /* matching smp_wmb() in _nfs4_pnfs_v3/4_ds_connect */ 405 smp_rmb(); 406 if (ds->ds_clp) 407 goto out; 408 409 /* FIXME: For now we assume the server sent only one version of NFS 410 * to use for the DS. 411 */ 412 status = nfs4_pnfs_ds_connect(s, ds, devid, dataserver_timeo, 413 dataserver_retrans, 414 mirror->mirror_ds->ds_versions[0].version, 415 mirror->mirror_ds->ds_versions[0].minor_version); 416 417 /* connect success, check rsize/wsize limit */ 418 if (ds->ds_clp) { 419 max_payload = 420 nfs_block_size(rpc_max_payload(ds->ds_clp->cl_rpcclient), 421 NULL); 422 if (mirror->mirror_ds->ds_versions[0].rsize > max_payload) 423 mirror->mirror_ds->ds_versions[0].rsize = max_payload; 424 if (mirror->mirror_ds->ds_versions[0].wsize > max_payload) 425 mirror->mirror_ds->ds_versions[0].wsize = max_payload; 426 goto out; 427 } 428 out_fail: 429 ff_layout_track_ds_error(FF_LAYOUT_FROM_HDR(lseg->pls_layout), 430 mirror, lseg->pls_range.offset, 431 lseg->pls_range.length, NFS4ERR_NXIO, 432 OP_ILLEGAL, GFP_NOIO); 433 if (fail_return || !ff_layout_has_available_ds(lseg)) 434 pnfs_error_mark_layout_for_return(ino, lseg); 435 ds = NULL; 436 out: 437 return ds; 438 } 439 440 struct rpc_cred * 441 ff_layout_get_ds_cred(struct pnfs_layout_segment *lseg, u32 ds_idx, 442 struct rpc_cred *mdscred) 443 { 444 struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, ds_idx); 445 struct rpc_cred *cred; 446 447 if (mirror) { 448 cred = ff_layout_get_mirror_cred(mirror, lseg->pls_range.iomode); 449 if (!cred) 450 cred = get_rpccred(mdscred); 451 } else { 452 cred = get_rpccred(mdscred); 453 } 454 return cred; 455 } 456 457 /** 458 * Find or create a DS rpc client with th MDS server rpc client auth flavor 459 * in the nfs_client cl_ds_clients list. 460 */ 461 struct rpc_clnt * 462 nfs4_ff_find_or_create_ds_client(struct pnfs_layout_segment *lseg, u32 ds_idx, 463 struct nfs_client *ds_clp, struct inode *inode) 464 { 465 struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, ds_idx); 466 467 switch (mirror->mirror_ds->ds_versions[0].version) { 468 case 3: 469 /* For NFSv3 DS, flavor is set when creating DS connections */ 470 return ds_clp->cl_rpcclient; 471 case 4: 472 return nfs4_find_or_create_ds_client(ds_clp, inode); 473 default: 474 BUG(); 475 } 476 } 477 478 void ff_layout_free_ds_ioerr(struct list_head *head) 479 { 480 struct nfs4_ff_layout_ds_err *err; 481 482 while (!list_empty(head)) { 483 err = list_first_entry(head, 484 struct nfs4_ff_layout_ds_err, 485 list); 486 list_del(&err->list); 487 kfree(err); 488 } 489 } 490 491 /* called with inode i_lock held */ 492 int ff_layout_encode_ds_ioerr(struct xdr_stream *xdr, const struct list_head *head) 493 { 494 struct nfs4_ff_layout_ds_err *err; 495 __be32 *p; 496 497 list_for_each_entry(err, head, list) { 498 /* offset(8) + length(8) + stateid(NFS4_STATEID_SIZE) 499 * + array length + deviceid(NFS4_DEVICEID4_SIZE) 500 * + status(4) + opnum(4) 501 */ 502 p = xdr_reserve_space(xdr, 503 28 + NFS4_STATEID_SIZE + NFS4_DEVICEID4_SIZE); 504 if (unlikely(!p)) 505 return -ENOBUFS; 506 p = xdr_encode_hyper(p, err->offset); 507 p = xdr_encode_hyper(p, err->length); 508 p = xdr_encode_opaque_fixed(p, &err->stateid, 509 NFS4_STATEID_SIZE); 510 /* Encode 1 error */ 511 *p++ = cpu_to_be32(1); 512 p = xdr_encode_opaque_fixed(p, &err->deviceid, 513 NFS4_DEVICEID4_SIZE); 514 *p++ = cpu_to_be32(err->status); 515 *p++ = cpu_to_be32(err->opnum); 516 dprintk("%s: offset %llu length %llu status %d op %d\n", 517 __func__, err->offset, err->length, err->status, 518 err->opnum); 519 } 520 521 return 0; 522 } 523 524 static 525 unsigned int do_layout_fetch_ds_ioerr(struct pnfs_layout_hdr *lo, 526 const struct pnfs_layout_range *range, 527 struct list_head *head, 528 unsigned int maxnum) 529 { 530 struct nfs4_flexfile_layout *flo = FF_LAYOUT_FROM_HDR(lo); 531 struct inode *inode = lo->plh_inode; 532 struct nfs4_ff_layout_ds_err *err, *n; 533 unsigned int ret = 0; 534 535 spin_lock(&inode->i_lock); 536 list_for_each_entry_safe(err, n, &flo->error_list, list) { 537 if (!pnfs_is_range_intersecting(err->offset, 538 pnfs_end_offset(err->offset, err->length), 539 range->offset, 540 pnfs_end_offset(range->offset, range->length))) 541 continue; 542 if (!maxnum) 543 break; 544 list_move(&err->list, head); 545 maxnum--; 546 ret++; 547 } 548 spin_unlock(&inode->i_lock); 549 return ret; 550 } 551 552 unsigned int ff_layout_fetch_ds_ioerr(struct pnfs_layout_hdr *lo, 553 const struct pnfs_layout_range *range, 554 struct list_head *head, 555 unsigned int maxnum) 556 { 557 unsigned int ret; 558 559 ret = do_layout_fetch_ds_ioerr(lo, range, head, maxnum); 560 /* If we're over the max, discard all remaining entries */ 561 if (ret == maxnum) { 562 LIST_HEAD(discard); 563 do_layout_fetch_ds_ioerr(lo, range, &discard, -1); 564 ff_layout_free_ds_ioerr(&discard); 565 } 566 return ret; 567 } 568 569 static bool ff_read_layout_has_available_ds(struct pnfs_layout_segment *lseg) 570 { 571 struct nfs4_ff_layout_mirror *mirror; 572 struct nfs4_deviceid_node *devid; 573 u32 idx; 574 575 for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) { 576 mirror = FF_LAYOUT_COMP(lseg, idx); 577 if (mirror) { 578 if (!mirror->mirror_ds) 579 return true; 580 if (IS_ERR(mirror->mirror_ds)) 581 continue; 582 devid = &mirror->mirror_ds->id_node; 583 if (!ff_layout_test_devid_unavailable(devid)) 584 return true; 585 } 586 } 587 588 return false; 589 } 590 591 static bool ff_rw_layout_has_available_ds(struct pnfs_layout_segment *lseg) 592 { 593 struct nfs4_ff_layout_mirror *mirror; 594 struct nfs4_deviceid_node *devid; 595 u32 idx; 596 597 for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) { 598 mirror = FF_LAYOUT_COMP(lseg, idx); 599 if (!mirror || IS_ERR(mirror->mirror_ds)) 600 return false; 601 if (!mirror->mirror_ds) 602 continue; 603 devid = &mirror->mirror_ds->id_node; 604 if (ff_layout_test_devid_unavailable(devid)) 605 return false; 606 } 607 608 return FF_LAYOUT_MIRROR_COUNT(lseg) != 0; 609 } 610 611 static bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg) 612 { 613 if (lseg->pls_range.iomode == IOMODE_READ) 614 return ff_read_layout_has_available_ds(lseg); 615 /* Note: RW layout needs all mirrors available */ 616 return ff_rw_layout_has_available_ds(lseg); 617 } 618 619 bool ff_layout_avoid_mds_available_ds(struct pnfs_layout_segment *lseg) 620 { 621 return ff_layout_no_fallback_to_mds(lseg) || 622 ff_layout_has_available_ds(lseg); 623 } 624 625 bool ff_layout_avoid_read_on_rw(struct pnfs_layout_segment *lseg) 626 { 627 return lseg->pls_range.iomode == IOMODE_RW && 628 ff_layout_no_read_on_rw(lseg); 629 } 630 631 module_param(dataserver_retrans, uint, 0644); 632 MODULE_PARM_DESC(dataserver_retrans, "The number of times the NFSv4.1 client " 633 "retries a request before it attempts further " 634 " recovery action."); 635 module_param(dataserver_timeo, uint, 0644); 636 MODULE_PARM_DESC(dataserver_timeo, "The time (in tenths of a second) the " 637 "NFSv4.1 client waits for a response from a " 638 " data server before it retries an NFS request."); 639