fs/netfs/buffered_read.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Network filesystem high-level buffered read support.
   3  *
   4  * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/export.h>
   9 #include <linux/task_io_accounting_ops.h>
  10 #include "internal.h"
  11
  12 /*
  13  * Unlock the folios in a read operation.  We need to set PG_fscache on any
  14  * folios we're going to write back before we unlock them.
  15  */
  16 void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
  17 {
  18         struct netfs_io_subrequest *subreq;
  19         struct folio *folio;
  20         pgoff_t start_page = rreq->start / PAGE_SIZE;
  21         pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
  22         size_t account = 0;
  23         bool subreq_failed = false;
  24
  25         XA_STATE(xas, &rreq->mapping->i_pages, start_page);
  26
  27         if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
  28                 __clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
  29                 list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
  30                         __clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
  31                 }
  32         }
  33
  34         /* Walk through the pagecache and the I/O request lists simultaneously.
  35          * We may have a mixture of cached and uncached sections and we only
  36          * really want to write out the uncached sections.  This is slightly
  37          * complicated by the possibility that we might have huge pages with a
  38          * mixture inside.
  39          */
  40         subreq = list_first_entry(&rreq->subrequests,
  41                                   struct netfs_io_subrequest, rreq_link);
  42         subreq_failed = (subreq->error < 0);
  43
  44         trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
  45
  46         rcu_read_lock();
  47         xas_for_each(&xas, folio, last_page) {
  48                 loff_t pg_end;
  49                 bool pg_failed = false;
  50
  51                 if (xas_retry(&xas, folio))
  52                         continue;
  53
  54                 pg_end = folio_pos(folio) + folio_size(folio) - 1;
  55
  56                 for (;;) {
  57                         loff_t sreq_end;
  58
  59                         if (!subreq) {
  60                                 pg_failed = true;
  61                                 break;
  62                         }
  63                         if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
  64                                 folio_start_fscache(folio);
  65                         pg_failed |= subreq_failed;
  66                         sreq_end = subreq->start + subreq->len - 1;
  67                         if (pg_end < sreq_end)
  68                                 break;
  69
  70                         account += subreq->transferred;
  71                         if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
  72                                 subreq = list_next_entry(subreq, rreq_link);
  73                                 subreq_failed = (subreq->error < 0);
  74                         } else {
  75                                 subreq = NULL;
  76                                 subreq_failed = false;
  77                         }
  78
  79                         if (pg_end == sreq_end)
  80                                 break;
  81                 }
  82
  83                 if (!pg_failed) {
  84                         flush_dcache_folio(folio);
  85                         folio_mark_uptodate(folio);
  86                 }
  87
  88                 if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
  89                         if (folio_index(folio) == rreq->no_unlock_folio &&
  90                             test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
  91                                 _debug("no unlock");
  92                         else
  93                                 folio_unlock(folio);
  94                 }
  95         }
  96         rcu_read_unlock();
  97
  98         task_io_account_read(account);
  99         if (rreq->netfs_ops->done)
 100                 rreq->netfs_ops->done(rreq);
 101 }
 102
 103 static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
 104                                          loff_t *_start, size_t *_len, loff_t i_size)
 105 {
 106         struct netfs_cache_resources *cres = &rreq->cache_resources;
 107
 108         if (cres->ops && cres->ops->expand_readahead)
 109                 cres->ops->expand_readahead(cres, _start, _len, i_size);
 110 }
 111
 112 static void netfs_rreq_expand(struct netfs_io_request *rreq,
 113                               struct readahead_control *ractl)
 114 {
 115         /* Give the cache a chance to change the request parameters.  The
 116          * resultant request must contain the original region.
 117          */
 118         netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
 119
 120         /* Give the netfs a chance to change the request parameters.  The
 121          * resultant request must contain the original region.
 122          */
 123         if (rreq->netfs_ops->expand_readahead)
 124                 rreq->netfs_ops->expand_readahead(rreq);
 125
 126         /* Expand the request if the cache wants it to start earlier.  Note
 127          * that the expansion may get further extended if the VM wishes to
 128          * insert THPs and the preferred start and/or end wind up in the middle
 129          * of THPs.
 130          *
 131          * If this is the case, however, the THP size should be an integer
 132          * multiple of the cache granule size, so we get a whole number of
 133          * granules to deal with.
 134          */
 135         if (rreq->start  != readahead_pos(ractl) ||
 136             rreq->len != readahead_length(ractl)) {
 137                 readahead_expand(ractl, rreq->start, rreq->len);
 138                 rreq->start  = readahead_pos(ractl);
 139                 rreq->len = readahead_length(ractl);
 140
 141                 trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
 142                                  netfs_read_trace_expanded);
 143         }
 144 }
 145
 146 /**
 147  * netfs_readahead - Helper to manage a read request
 148  * @ractl: The description of the readahead request
 149  *
 150  * Fulfil a readahead request by drawing data from the cache if possible, or
 151  * the netfs if not.  Space beyond the EOF is zero-filled.  Multiple I/O
 152  * requests from different sources will get munged together.  If necessary, the
 153  * readahead window can be expanded in either direction to a more convenient
 154  * alighment for RPC efficiency or to make storage in the cache feasible.
 155  *
 156  * The calling netfs must initialise a netfs context contiguous to the vfs
 157  * inode before calling this.
 158  *
 159  * This is usable whether or not caching is enabled.
 160  */
 161 void netfs_readahead(struct readahead_control *ractl)
 162 {
 163         struct netfs_io_request *rreq;
 164         struct netfs_inode *ctx = netfs_inode(ractl->mapping->host);
 165         int ret;
 166
 167         _enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
 168
 169         if (readahead_count(ractl) == 0)
 170                 return;
 171
 172         rreq = netfs_alloc_request(ractl->mapping, ractl->file,
 173                                    readahead_pos(ractl),
 174                                    readahead_length(ractl),
 175                                    NETFS_READAHEAD);
 176         if (IS_ERR(rreq))
 177                 return;
 178
 179         if (ctx->ops->begin_cache_operation) {
 180                 ret = ctx->ops->begin_cache_operation(rreq);
 181                 if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
 182                         goto cleanup_free;
 183         }
 184
 185         netfs_stat(&netfs_n_rh_readahead);
 186         trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
 187                          netfs_read_trace_readahead);
 188
 189         netfs_rreq_expand(rreq, ractl);
 190
 191         /* Drop the refs on the folios here rather than in the cache or
 192          * filesystem.  The locks will be dropped in netfs_rreq_unlock().
 193          */
 194         while (readahead_folio(ractl))
 195                 ;
 196
 197         netfs_begin_read(rreq, false);
 198         return;
 199
 200 cleanup_free:
 201         netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
 202         return;
 203 }
 204 EXPORT_SYMBOL(netfs_readahead);
 205
 206 /**
 207  * netfs_read_folio - Helper to manage a read_folio request
 208  * @file: The file to read from
 209  * @folio: The folio to read
 210  *
 211  * Fulfil a read_folio request by drawing data from the cache if
 212  * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
 213  * Multiple I/O requests from different sources will get munged together.
 214  *
 215  * The calling netfs must initialise a netfs context contiguous to the vfs
 216  * inode before calling this.
 217  *
 218  * This is usable whether or not caching is enabled.
 219  */
 220 int netfs_read_folio(struct file *file, struct folio *folio)
 221 {
 222         struct address_space *mapping = folio_file_mapping(folio);
 223         struct netfs_io_request *rreq;
 224         struct netfs_inode *ctx = netfs_inode(mapping->host);
 225         int ret;
 226
 227         _enter("%lx", folio_index(folio));
 228
 229         rreq = netfs_alloc_request(mapping, file,
 230                                    folio_file_pos(folio), folio_size(folio),
 231                                    NETFS_READPAGE);
 232         if (IS_ERR(rreq)) {
 233                 ret = PTR_ERR(rreq);
 234                 goto alloc_error;
 235         }
 236
 237         if (ctx->ops->begin_cache_operation) {
 238                 ret = ctx->ops->begin_cache_operation(rreq);
 239                 if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
 240                         goto discard;
 241         }
 242
 243         netfs_stat(&netfs_n_rh_readpage);
 244         trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
 245         return netfs_begin_read(rreq, true);
 246
 247 discard:
 248         netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
 249 alloc_error:
 250         folio_unlock(folio);
 251         return ret;
 252 }
 253 EXPORT_SYMBOL(netfs_read_folio);
 254
 255 /*
 256  * Prepare a folio for writing without reading first
 257  * @folio: The folio being prepared
 258  * @pos: starting position for the write
 259  * @len: length of write
 260  * @always_fill: T if the folio should always be completely filled/cleared
 261  *
 262  * In some cases, write_begin doesn't need to read at all:
 263  * - full folio write
 264  * - write that lies in a folio that is completely beyond EOF
 265  * - write that covers the folio from start to EOF or beyond it
 266  *
 267  * If any of these criteria are met, then zero out the unwritten parts
 268  * of the folio and return true. Otherwise, return false.
 269  */
 270 static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
 271                                  bool always_fill)
 272 {
 273         struct inode *inode = folio_inode(folio);
 274         loff_t i_size = i_size_read(inode);
 275         size_t offset = offset_in_folio(folio, pos);
 276         size_t plen = folio_size(folio);
 277
 278         if (unlikely(always_fill)) {
 279                 if (pos - offset + len <= i_size)
 280                         return false; /* Page entirely before EOF */
 281                 zero_user_segment(&folio->page, 0, plen);
 282                 folio_mark_uptodate(folio);
 283                 return true;
 284         }
 285
 286         /* Full folio write */
 287         if (offset == 0 && len >= plen)
 288                 return true;
 289
 290         /* Page entirely beyond the end of the file */
 291         if (pos - offset >= i_size)
 292                 goto zero_out;
 293
 294         /* Write that covers from the start of the folio to EOF or beyond */
 295         if (offset == 0 && (pos + len) >= i_size)
 296                 goto zero_out;
 297
 298         return false;
 299 zero_out:
 300         zero_user_segments(&folio->page, 0, offset, offset + len, plen);
 301         return true;
 302 }
 303
 304 /**
 305  * netfs_write_begin - Helper to prepare for writing
 306  * @ctx: The netfs context
 307  * @file: The file to read from
 308  * @mapping: The mapping to read from
 309  * @pos: File position at which the write will begin
 310  * @len: The length of the write (may extend beyond the end of the folio chosen)
 311  * @_folio: Where to put the resultant folio
 312  * @_fsdata: Place for the netfs to store a cookie
 313  *
 314  * Pre-read data for a write-begin request by drawing data from the cache if
 315  * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
 316  * Multiple I/O requests from different sources will get munged together.  If
 317  * necessary, the readahead window can be expanded in either direction to a
 318  * more convenient alighment for RPC efficiency or to make storage in the cache
 319  * feasible.
 320  *
 321  * The calling netfs must provide a table of operations, only one of which,
 322  * issue_op, is mandatory.
 323  *
 324  * The check_write_begin() operation can be provided to check for and flush
 325  * conflicting writes once the folio is grabbed and locked.  It is passed a
 326  * pointer to the fsdata cookie that gets returned to the VM to be passed to
 327  * write_end.  It is permitted to sleep.  It should return 0 if the request
 328  * should go ahead or it may return an error.  It may also unlock and put the
 329  * folio, provided it sets ``*foliop`` to NULL, in which case a return of 0
 330  * will cause the folio to be re-got and the process to be retried.
 331  *
 332  * The calling netfs must initialise a netfs context contiguous to the vfs
 333  * inode before calling this.
 334  *
 335  * This is usable whether or not caching is enabled.
 336  */
 337 int netfs_write_begin(struct netfs_inode *ctx,
 338                       struct file *file, struct address_space *mapping,
 339                       loff_t pos, unsigned int len, struct folio **_folio,
 340                       void **_fsdata)
 341 {
 342         struct netfs_io_request *rreq;
 343         struct folio *folio;
 344         pgoff_t index = pos >> PAGE_SHIFT;
 345         int ret;
 346
 347         DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
 348
 349 retry:
 350         folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
 351                                     mapping_gfp_mask(mapping));
 352         if (IS_ERR(folio))
 353                 return PTR_ERR(folio);
 354
 355         if (ctx->ops->check_write_begin) {
 356                 /* Allow the netfs (eg. ceph) to flush conflicts. */
 357                 ret = ctx->ops->check_write_begin(file, pos, len, &folio, _fsdata);
 358                 if (ret < 0) {
 359                         trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
 360                         goto error;
 361                 }
 362                 if (!folio)
 363                         goto retry;
 364         }
 365
 366         if (folio_test_uptodate(folio))
 367                 goto have_folio;
 368
 369         /* If the page is beyond the EOF, we want to clear it - unless it's
 370          * within the cache granule containing the EOF, in which case we need
 371          * to preload the granule.
 372          */
 373         if (!netfs_is_cache_enabled(ctx) &&
 374             netfs_skip_folio_read(folio, pos, len, false)) {
 375                 netfs_stat(&netfs_n_rh_write_zskip);
 376                 goto have_folio_no_wait;
 377         }
 378
 379         rreq = netfs_alloc_request(mapping, file,
 380                                    folio_file_pos(folio), folio_size(folio),
 381                                    NETFS_READ_FOR_WRITE);
 382         if (IS_ERR(rreq)) {
 383                 ret = PTR_ERR(rreq);
 384                 goto error;
 385         }
 386         rreq->no_unlock_folio   = folio_index(folio);
 387         __set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
 388
 389         if (ctx->ops->begin_cache_operation) {
 390                 ret = ctx->ops->begin_cache_operation(rreq);
 391                 if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
 392                         goto error_put;
 393         }
 394
 395         netfs_stat(&netfs_n_rh_write_begin);
 396         trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
 397
 398         /* Expand the request to meet caching requirements and download
 399          * preferences.
 400          */
 401         ractl._nr_pages = folio_nr_pages(folio);
 402         netfs_rreq_expand(rreq, &ractl);
 403
 404         /* We hold the folio locks, so we can drop the references */
 405         folio_get(folio);
 406         while (readahead_folio(&ractl))
 407                 ;
 408
 409         ret = netfs_begin_read(rreq, true);
 410         if (ret < 0)
 411                 goto error;
 412
 413 have_folio:
 414         ret = folio_wait_fscache_killable(folio);
 415         if (ret < 0)
 416                 goto error;
 417 have_folio_no_wait:
 418         *_folio = folio;
 419         _leave(" = 0");
 420         return 0;
 421
 422 error_put:
 423         netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
 424 error:
 425         if (folio) {
 426                 folio_unlock(folio);
 427                 folio_put(folio);
 428         }
 429         _leave(" = %d", ret);
 430         return ret;
 431 }
 432 EXPORT_SYMBOL(netfs_write_begin);