[PATCH v3 17/20] netfs: Split fs/netfs/read_helper.c
David Howells
dhowells at redhat.com
Thu Mar 10 08:19:59 PST 2022
Split fs/netfs/read_helper.c into two pieces, one to deal with buffered
writes and one to deal with the I/O mechanism.
Changes
=======
ver #2)
- Add kdoc reference to new file.
Signed-off-by: David Howells <dhowells at redhat.com>
Reviewed-by: Jeff Layton <jlayton at kernel.org>
cc: linux-cachefs at redhat.com
Link: https://lore.kernel.org/r/164623005586.3564931.6149556072728481767.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678217075.1200972.5101072043126828757.stgit@warthog.procyon.org.uk/ # v2
---
fs/netfs/Makefile | 1
fs/netfs/buffered_read.c | 428 ++++++++++++++++++++++++++++++++++++++++++++++
fs/netfs/io.c | 418 ---------------------------------------------
3 files changed, 429 insertions(+), 418 deletions(-)
create mode 100644 fs/netfs/buffered_read.c
diff --git a/fs/netfs/Makefile b/fs/netfs/Makefile
index 51ece4f7bc77..88b904532bc7 100644
--- a/fs/netfs/Makefile
+++ b/fs/netfs/Makefile
@@ -1,6 +1,7 @@
# SPDX-License-Identifier: GPL-2.0
netfs-y := \
+ buffered_read.o \
io.o \
objects.o
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
new file mode 100644
index 000000000000..09ba7097a970
--- /dev/null
+++ b/fs/netfs/buffered_read.c
@@ -0,0 +1,428 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Network filesystem high-level buffered read support.
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells at redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/task_io_accounting_ops.h>
+#include "internal.h"
+
+/*
+ * Unlock the folios in a read operation. We need to set PG_fscache on any
+ * folios we're going to write back before we unlock them.
+ */
+void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
+{
+ struct netfs_io_subrequest *subreq;
+ struct folio *folio;
+ unsigned int iopos, account = 0;
+ pgoff_t start_page = rreq->start / PAGE_SIZE;
+ pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
+ bool subreq_failed = false;
+
+ XA_STATE(xas, &rreq->mapping->i_pages, start_page);
+
+ if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
+ __clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
+ list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
+ __clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
+ }
+ }
+
+ /* Walk through the pagecache and the I/O request lists simultaneously.
+ * We may have a mixture of cached and uncached sections and we only
+ * really want to write out the uncached sections. This is slightly
+ * complicated by the possibility that we might have huge pages with a
+ * mixture inside.
+ */
+ subreq = list_first_entry(&rreq->subrequests,
+ struct netfs_io_subrequest, rreq_link);
+ iopos = 0;
+ subreq_failed = (subreq->error < 0);
+
+ trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
+
+ rcu_read_lock();
+ xas_for_each(&xas, folio, last_page) {
+ unsigned int pgpos = (folio_index(folio) - start_page) * PAGE_SIZE;
+ unsigned int pgend = pgpos + folio_size(folio);
+ bool pg_failed = false;
+
+ for (;;) {
+ if (!subreq) {
+ pg_failed = true;
+ break;
+ }
+ if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
+ folio_start_fscache(folio);
+ pg_failed |= subreq_failed;
+ if (pgend < iopos + subreq->len)
+ break;
+
+ account += subreq->transferred;
+ iopos += subreq->len;
+ if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
+ subreq = list_next_entry(subreq, rreq_link);
+ subreq_failed = (subreq->error < 0);
+ } else {
+ subreq = NULL;
+ subreq_failed = false;
+ }
+ if (pgend == iopos)
+ break;
+ }
+
+ if (!pg_failed) {
+ flush_dcache_folio(folio);
+ folio_mark_uptodate(folio);
+ }
+
+ if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
+ if (folio_index(folio) == rreq->no_unlock_folio &&
+ test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
+ _debug("no unlock");
+ else
+ folio_unlock(folio);
+ }
+ }
+ rcu_read_unlock();
+
+ task_io_account_read(account);
+ if (rreq->netfs_ops->done)
+ rreq->netfs_ops->done(rreq);
+}
+
+static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
+ loff_t *_start, size_t *_len, loff_t i_size)
+{
+ struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+ if (cres->ops && cres->ops->expand_readahead)
+ cres->ops->expand_readahead(cres, _start, _len, i_size);
+}
+
+static void netfs_rreq_expand(struct netfs_io_request *rreq,
+ struct readahead_control *ractl)
+{
+ /* Give the cache a chance to change the request parameters. The
+ * resultant request must contain the original region.
+ */
+ netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
+
+ /* Give the netfs a chance to change the request parameters. The
+ * resultant request must contain the original region.
+ */
+ if (rreq->netfs_ops->expand_readahead)
+ rreq->netfs_ops->expand_readahead(rreq);
+
+ /* Expand the request if the cache wants it to start earlier. Note
+ * that the expansion may get further extended if the VM wishes to
+ * insert THPs and the preferred start and/or end wind up in the middle
+ * of THPs.
+ *
+ * If this is the case, however, the THP size should be an integer
+ * multiple of the cache granule size, so we get a whole number of
+ * granules to deal with.
+ */
+ if (rreq->start != readahead_pos(ractl) ||
+ rreq->len != readahead_length(ractl)) {
+ readahead_expand(ractl, rreq->start, rreq->len);
+ rreq->start = readahead_pos(ractl);
+ rreq->len = readahead_length(ractl);
+
+ trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+ netfs_read_trace_expanded);
+ }
+}
+
+/**
+ * netfs_readahead - Helper to manage a read request
+ * @ractl: The description of the readahead request
+ *
+ * Fulfil a readahead request by drawing data from the cache if possible, or
+ * the netfs if not. Space beyond the EOF is zero-filled. Multiple I/O
+ * requests from different sources will get munged together. If necessary, the
+ * readahead window can be expanded in either direction to a more convenient
+ * alighment for RPC efficiency or to make storage in the cache feasible.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+void netfs_readahead(struct readahead_control *ractl)
+{
+ struct netfs_io_request *rreq;
+ struct netfs_i_context *ctx = netfs_i_context(ractl->mapping->host);
+ int ret;
+
+ _enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
+
+ if (readahead_count(ractl) == 0)
+ return;
+
+ rreq = netfs_alloc_request(ractl->mapping, ractl->file,
+ readahead_pos(ractl),
+ readahead_length(ractl),
+ NETFS_READAHEAD);
+ if (IS_ERR(rreq))
+ return;
+
+ if (ctx->ops->begin_cache_operation) {
+ ret = ctx->ops->begin_cache_operation(rreq);
+ if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+ goto cleanup_free;
+ }
+
+ netfs_stat(&netfs_n_rh_readahead);
+ trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+ netfs_read_trace_readahead);
+
+ netfs_rreq_expand(rreq, ractl);
+
+ /* Drop the refs on the folios here rather than in the cache or
+ * filesystem. The locks will be dropped in netfs_rreq_unlock().
+ */
+ while (readahead_folio(ractl))
+ ;
+
+ netfs_begin_read(rreq, false);
+ return;
+
+cleanup_free:
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
+ return;
+}
+EXPORT_SYMBOL(netfs_readahead);
+
+/**
+ * netfs_readpage - Helper to manage a readpage request
+ * @file: The file to read from
+ * @subpage: A subpage of the folio to read
+ *
+ * Fulfil a readpage request by drawing data from the cache if possible, or the
+ * netfs if not. Space beyond the EOF is zero-filled. Multiple I/O requests
+ * from different sources will get munged together.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+int netfs_readpage(struct file *file, struct page *subpage)
+{
+ struct folio *folio = page_folio(subpage);
+ struct address_space *mapping = folio_file_mapping(folio);
+ struct netfs_io_request *rreq;
+ struct netfs_i_context *ctx = netfs_i_context(mapping->host);
+ int ret;
+
+ _enter("%lx", folio_index(folio));
+
+ rreq = netfs_alloc_request(mapping, file,
+ folio_file_pos(folio), folio_size(folio),
+ NETFS_READPAGE);
+ if (IS_ERR(rreq)) {
+ ret = PTR_ERR(rreq);
+ goto alloc_error;
+ }
+
+ if (ctx->ops->begin_cache_operation) {
+ ret = ctx->ops->begin_cache_operation(rreq);
+ if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+ goto discard;
+ }
+
+ netfs_stat(&netfs_n_rh_readpage);
+ trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
+ return netfs_begin_read(rreq, true);
+
+discard:
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
+alloc_error:
+ folio_unlock(folio);
+ return ret;
+}
+EXPORT_SYMBOL(netfs_readpage);
+
+/*
+ * Prepare a folio for writing without reading first
+ * @folio: The folio being prepared
+ * @pos: starting position for the write
+ * @len: length of write
+ * @always_fill: T if the folio should always be completely filled/cleared
+ *
+ * In some cases, write_begin doesn't need to read at all:
+ * - full folio write
+ * - write that lies in a folio that is completely beyond EOF
+ * - write that covers the folio from start to EOF or beyond it
+ *
+ * If any of these criteria are met, then zero out the unwritten parts
+ * of the folio and return true. Otherwise, return false.
+ */
+static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
+ bool always_fill)
+{
+ struct inode *inode = folio_inode(folio);
+ loff_t i_size = i_size_read(inode);
+ size_t offset = offset_in_folio(folio, pos);
+ size_t plen = folio_size(folio);
+
+ if (unlikely(always_fill)) {
+ if (pos - offset + len <= i_size)
+ return false; /* Page entirely before EOF */
+ zero_user_segment(&folio->page, 0, plen);
+ folio_mark_uptodate(folio);
+ return true;
+ }
+
+ /* Full folio write */
+ if (offset == 0 && len >= plen)
+ return true;
+
+ /* Page entirely beyond the end of the file */
+ if (pos - offset >= i_size)
+ goto zero_out;
+
+ /* Write that covers from the start of the folio to EOF or beyond */
+ if (offset == 0 && (pos + len) >= i_size)
+ goto zero_out;
+
+ return false;
+zero_out:
+ zero_user_segments(&folio->page, 0, offset, offset + len, len);
+ return true;
+}
+
+/**
+ * netfs_write_begin - Helper to prepare for writing
+ * @file: The file to read from
+ * @mapping: The mapping to read from
+ * @pos: File position at which the write will begin
+ * @len: The length of the write (may extend beyond the end of the folio chosen)
+ * @aop_flags: AOP_* flags
+ * @_folio: Where to put the resultant folio
+ * @_fsdata: Place for the netfs to store a cookie
+ *
+ * Pre-read data for a write-begin request by drawing data from the cache if
+ * possible, or the netfs if not. Space beyond the EOF is zero-filled.
+ * Multiple I/O requests from different sources will get munged together. If
+ * necessary, the readahead window can be expanded in either direction to a
+ * more convenient alighment for RPC efficiency or to make storage in the cache
+ * feasible.
+ *
+ * The calling netfs must provide a table of operations, only one of which,
+ * issue_op, is mandatory.
+ *
+ * The check_write_begin() operation can be provided to check for and flush
+ * conflicting writes once the folio is grabbed and locked. It is passed a
+ * pointer to the fsdata cookie that gets returned to the VM to be passed to
+ * write_end. It is permitted to sleep. It should return 0 if the request
+ * should go ahead; unlock the folio and return -EAGAIN to cause the folio to
+ * be regot; or return an error.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+int netfs_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned int len, unsigned int aop_flags,
+ struct folio **_folio, void **_fsdata)
+{
+ struct netfs_io_request *rreq;
+ struct netfs_i_context *ctx = netfs_i_context(file_inode(file ));
+ struct folio *folio;
+ unsigned int fgp_flags;
+ pgoff_t index = pos >> PAGE_SHIFT;
+ int ret;
+
+ DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
+
+retry:
+ fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
+ if (aop_flags & AOP_FLAG_NOFS)
+ fgp_flags |= FGP_NOFS;
+ folio = __filemap_get_folio(mapping, index, fgp_flags,
+ mapping_gfp_mask(mapping));
+ if (!folio)
+ return -ENOMEM;
+
+ if (ctx->ops->check_write_begin) {
+ /* Allow the netfs (eg. ceph) to flush conflicts. */
+ ret = ctx->ops->check_write_begin(file, pos, len, folio, _fsdata);
+ if (ret < 0) {
+ trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
+ if (ret == -EAGAIN)
+ goto retry;
+ goto error;
+ }
+ }
+
+ if (folio_test_uptodate(folio))
+ goto have_folio;
+
+ /* If the page is beyond the EOF, we want to clear it - unless it's
+ * within the cache granule containing the EOF, in which case we need
+ * to preload the granule.
+ */
+ if (!netfs_is_cache_enabled(ctx) &&
+ netfs_skip_folio_read(folio, pos, len, false)) {
+ netfs_stat(&netfs_n_rh_write_zskip);
+ goto have_folio_no_wait;
+ }
+
+ rreq = netfs_alloc_request(mapping, file,
+ folio_file_pos(folio), folio_size(folio),
+ NETFS_READ_FOR_WRITE);
+ if (IS_ERR(rreq)) {
+ ret = PTR_ERR(rreq);
+ goto error;
+ }
+ rreq->no_unlock_folio = folio_index(folio);
+ __set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
+
+ if (ctx->ops->begin_cache_operation) {
+ ret = ctx->ops->begin_cache_operation(rreq);
+ if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+ goto error_put;
+ }
+
+ netfs_stat(&netfs_n_rh_write_begin);
+ trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
+
+ /* Expand the request to meet caching requirements and download
+ * preferences.
+ */
+ ractl._nr_pages = folio_nr_pages(folio);
+ netfs_rreq_expand(rreq, &ractl);
+
+ /* We hold the folio locks, so we can drop the references */
+ folio_get(folio);
+ while (readahead_folio(&ractl))
+ ;
+
+ ret = netfs_begin_read(rreq, true);
+ if (ret < 0)
+ goto error;
+
+have_folio:
+ ret = folio_wait_fscache_killable(folio);
+ if (ret < 0)
+ goto error;
+have_folio_no_wait:
+ *_folio = folio;
+ _leave(" = 0");
+ return 0;
+
+error_put:
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
+error:
+ folio_unlock(folio);
+ folio_put(folio);
+ _leave(" = %d", ret);
+ return ret;
+}
+EXPORT_SYMBOL(netfs_write_begin);
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index d448dc4f1010..6d43f9ea1b5a 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -246,91 +246,6 @@ static void netfs_rreq_write_to_cache(struct netfs_io_request *rreq)
BUG();
}
-/*
- * Unlock the folios in a read operation. We need to set PG_fscache on any
- * folios we're going to write back before we unlock them.
- */
-void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
-{
- struct netfs_io_subrequest *subreq;
- struct folio *folio;
- unsigned int iopos, account = 0;
- pgoff_t start_page = rreq->start / PAGE_SIZE;
- pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
- bool subreq_failed = false;
-
- XA_STATE(xas, &rreq->mapping->i_pages, start_page);
-
- if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
- __clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
- list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
- __clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
- }
- }
-
- /* Walk through the pagecache and the I/O request lists simultaneously.
- * We may have a mixture of cached and uncached sections and we only
- * really want to write out the uncached sections. This is slightly
- * complicated by the possibility that we might have huge pages with a
- * mixture inside.
- */
- subreq = list_first_entry(&rreq->subrequests,
- struct netfs_io_subrequest, rreq_link);
- iopos = 0;
- subreq_failed = (subreq->error < 0);
-
- trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
-
- rcu_read_lock();
- xas_for_each(&xas, folio, last_page) {
- unsigned int pgpos = (folio_index(folio) - start_page) * PAGE_SIZE;
- unsigned int pgend = pgpos + folio_size(folio);
- bool pg_failed = false;
-
- for (;;) {
- if (!subreq) {
- pg_failed = true;
- break;
- }
- if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
- folio_start_fscache(folio);
- pg_failed |= subreq_failed;
- if (pgend < iopos + subreq->len)
- break;
-
- account += subreq->transferred;
- iopos += subreq->len;
- if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
- subreq = list_next_entry(subreq, rreq_link);
- subreq_failed = (subreq->error < 0);
- } else {
- subreq = NULL;
- subreq_failed = false;
- }
- if (pgend == iopos)
- break;
- }
-
- if (!pg_failed) {
- flush_dcache_folio(folio);
- folio_mark_uptodate(folio);
- }
-
- if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
- if (folio_index(folio) == rreq->no_unlock_folio &&
- test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
- _debug("no unlock");
- else
- folio_unlock(folio);
- }
- }
- rcu_read_unlock();
-
- task_io_account_read(account);
- if (rreq->netfs_ops->done)
- rreq->netfs_ops->done(rreq);
-}
-
/*
* Handle a short read.
*/
@@ -750,336 +665,3 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
}
return ret;
}
-
-static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
- loff_t *_start, size_t *_len, loff_t i_size)
-{
- struct netfs_cache_resources *cres = &rreq->cache_resources;
-
- if (cres->ops && cres->ops->expand_readahead)
- cres->ops->expand_readahead(cres, _start, _len, i_size);
-}
-
-static void netfs_rreq_expand(struct netfs_io_request *rreq,
- struct readahead_control *ractl)
-{
- /* Give the cache a chance to change the request parameters. The
- * resultant request must contain the original region.
- */
- netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
-
- /* Give the netfs a chance to change the request parameters. The
- * resultant request must contain the original region.
- */
- if (rreq->netfs_ops->expand_readahead)
- rreq->netfs_ops->expand_readahead(rreq);
-
- /* Expand the request if the cache wants it to start earlier. Note
- * that the expansion may get further extended if the VM wishes to
- * insert THPs and the preferred start and/or end wind up in the middle
- * of THPs.
- *
- * If this is the case, however, the THP size should be an integer
- * multiple of the cache granule size, so we get a whole number of
- * granules to deal with.
- */
- if (rreq->start != readahead_pos(ractl) ||
- rreq->len != readahead_length(ractl)) {
- readahead_expand(ractl, rreq->start, rreq->len);
- rreq->start = readahead_pos(ractl);
- rreq->len = readahead_length(ractl);
-
- trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
- netfs_read_trace_expanded);
- }
-}
-
-/**
- * netfs_readahead - Helper to manage a read request
- * @ractl: The description of the readahead request
- *
- * Fulfil a readahead request by drawing data from the cache if possible, or
- * the netfs if not. Space beyond the EOF is zero-filled. Multiple I/O
- * requests from different sources will get munged together. If necessary, the
- * readahead window can be expanded in either direction to a more convenient
- * alighment for RPC efficiency or to make storage in the cache feasible.
- *
- * The calling netfs must initialise a netfs context contiguous to the vfs
- * inode before calling this.
- *
- * This is usable whether or not caching is enabled.
- */
-void netfs_readahead(struct readahead_control *ractl)
-{
- struct netfs_io_request *rreq;
- struct netfs_i_context *ctx = netfs_i_context(ractl->mapping->host);
- int ret;
-
- _enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
-
- if (readahead_count(ractl) == 0)
- return;
-
- rreq = netfs_alloc_request(ractl->mapping, ractl->file,
- readahead_pos(ractl),
- readahead_length(ractl),
- NETFS_READAHEAD);
- if (IS_ERR(rreq))
- return;
-
- if (ctx->ops->begin_cache_operation) {
- ret = ctx->ops->begin_cache_operation(rreq);
- if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
- goto cleanup_free;
- }
-
- netfs_stat(&netfs_n_rh_readahead);
- trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
- netfs_read_trace_readahead);
-
- netfs_rreq_expand(rreq, ractl);
-
- /* Drop the refs on the folios here rather than in the cache or
- * filesystem. The locks will be dropped in netfs_rreq_unlock().
- */
- while (readahead_folio(ractl))
- ;
-
- netfs_begin_read(rreq, false);
- return;
-
-cleanup_free:
- netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
- return;
-}
-EXPORT_SYMBOL(netfs_readahead);
-
-/**
- * netfs_readpage - Helper to manage a readpage request
- * @file: The file to read from
- * @subpage: A subpage of the folio to read
- *
- * Fulfil a readpage request by drawing data from the cache if possible, or the
- * netfs if not. Space beyond the EOF is zero-filled. Multiple I/O requests
- * from different sources will get munged together.
- *
- * The calling netfs must initialise a netfs context contiguous to the vfs
- * inode before calling this.
- *
- * This is usable whether or not caching is enabled.
- */
-int netfs_readpage(struct file *file, struct page *subpage)
-{
- struct folio *folio = page_folio(subpage);
- struct address_space *mapping = folio->mapping;
- struct netfs_io_request *rreq;
- struct netfs_i_context *ctx = netfs_i_context(mapping->host);
- int ret;
-
- _enter("%lx", folio_index(folio));
-
- rreq = netfs_alloc_request(mapping, file,
- folio_file_pos(folio), folio_size(folio),
- NETFS_READPAGE);
- if (IS_ERR(rreq)) {
- ret = PTR_ERR(rreq);
- goto alloc_error;
- }
-
- if (ctx->ops->begin_cache_operation) {
- ret = ctx->ops->begin_cache_operation(rreq);
- if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
- goto discard;
- }
-
- netfs_stat(&netfs_n_rh_readpage);
- trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
- return netfs_begin_read(rreq, true);
-
-discard:
- netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
-alloc_error:
- folio_unlock(folio);
- return ret;
-}
-EXPORT_SYMBOL(netfs_readpage);
-
-/*
- * Prepare a folio for writing without reading first
- * @folio: The folio being prepared
- * @pos: starting position for the write
- * @len: length of write
- * @always_fill: T if the folio should always be completely filled/cleared
- *
- * In some cases, write_begin doesn't need to read at all:
- * - full folio write
- * - write that lies in a folio that is completely beyond EOF
- * - write that covers the folio from start to EOF or beyond it
- *
- * If any of these criteria are met, then zero out the unwritten parts
- * of the folio and return true. Otherwise, return false.
- */
-static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
- bool always_fill)
-{
- struct inode *inode = folio_inode(folio);
- loff_t i_size = i_size_read(inode);
- size_t offset = offset_in_folio(folio, pos);
- size_t plen = folio_size(folio);
-
- if (unlikely(always_fill)) {
- if (pos - offset + len <= i_size)
- return false; /* Page entirely before EOF */
- zero_user_segment(&folio->page, 0, plen);
- folio_mark_uptodate(folio);
- return true;
- }
-
- /* Full folio write */
- if (offset == 0 && len >= plen)
- return true;
-
- /* Page entirely beyond the end of the file */
- if (pos - offset >= i_size)
- goto zero_out;
-
- /* Write that covers from the start of the folio to EOF or beyond */
- if (offset == 0 && (pos + len) >= i_size)
- goto zero_out;
-
- return false;
-zero_out:
- zero_user_segments(&folio->page, 0, offset, offset + len, len);
- return true;
-}
-
-/**
- * netfs_write_begin - Helper to prepare for writing
- * @file: The file to read from
- * @mapping: The mapping to read from
- * @pos: File position at which the write will begin
- * @len: The length of the write (may extend beyond the end of the folio chosen)
- * @aop_flags: AOP_* flags
- * @_folio: Where to put the resultant folio
- * @_fsdata: Place for the netfs to store a cookie
- *
- * Pre-read data for a write-begin request by drawing data from the cache if
- * possible, or the netfs if not. Space beyond the EOF is zero-filled.
- * Multiple I/O requests from different sources will get munged together. If
- * necessary, the readahead window can be expanded in either direction to a
- * more convenient alighment for RPC efficiency or to make storage in the cache
- * feasible.
- *
- * The calling netfs must provide a table of operations, only one of which,
- * issue_op, is mandatory.
- *
- * The check_write_begin() operation can be provided to check for and flush
- * conflicting writes once the folio is grabbed and locked. It is passed a
- * pointer to the fsdata cookie that gets returned to the VM to be passed to
- * write_end. It is permitted to sleep. It should return 0 if the request
- * should go ahead; unlock the folio and return -EAGAIN to cause the folio to
- * be regot; or return an error.
- *
- * The calling netfs must initialise a netfs context contiguous to the vfs
- * inode before calling this.
- *
- * This is usable whether or not caching is enabled.
- */
-int netfs_write_begin(struct file *file, struct address_space *mapping,
- loff_t pos, unsigned int len, unsigned int aop_flags,
- struct folio **_folio, void **_fsdata)
-{
- struct netfs_io_request *rreq;
- struct netfs_i_context *ctx = netfs_i_context(file_inode(file ));
- struct folio *folio;
- unsigned int fgp_flags;
- pgoff_t index = pos >> PAGE_SHIFT;
- int ret;
-
- DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
-
-retry:
- fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
- if (aop_flags & AOP_FLAG_NOFS)
- fgp_flags |= FGP_NOFS;
- folio = __filemap_get_folio(mapping, index, fgp_flags,
- mapping_gfp_mask(mapping));
- if (!folio)
- return -ENOMEM;
-
- if (ctx->ops->check_write_begin) {
- /* Allow the netfs (eg. ceph) to flush conflicts. */
- ret = ctx->ops->check_write_begin(file, pos, len, folio, _fsdata);
- if (ret < 0) {
- trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
- if (ret == -EAGAIN)
- goto retry;
- goto error;
- }
- }
-
- if (folio_test_uptodate(folio))
- goto have_folio;
-
- /* If the page is beyond the EOF, we want to clear it - unless it's
- * within the cache granule containing the EOF, in which case we need
- * to preload the granule.
- */
- if (!netfs_is_cache_enabled(ctx) &&
- netfs_skip_folio_read(folio, pos, len, false)) {
- netfs_stat(&netfs_n_rh_write_zskip);
- goto have_folio_no_wait;
- }
-
- rreq = netfs_alloc_request(mapping, file,
- folio_file_pos(folio), folio_size(folio),
- NETFS_READ_FOR_WRITE);
- if (IS_ERR(rreq)) {
- ret = PTR_ERR(rreq);
- goto error;
- }
- rreq->no_unlock_folio = folio_index(folio);
- __set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
-
- if (ctx->ops->begin_cache_operation) {
- ret = ctx->ops->begin_cache_operation(rreq);
- if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
- goto error_put;
- }
-
- netfs_stat(&netfs_n_rh_write_begin);
- trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
-
- /* Expand the request to meet caching requirements and download
- * preferences.
- */
- ractl._nr_pages = folio_nr_pages(folio);
- netfs_rreq_expand(rreq, &ractl);
-
- /* We hold the folio locks, so we can drop the references */
- folio_get(folio);
- while (readahead_folio(&ractl))
- ;
-
- ret = netfs_begin_read(rreq, true);
- if (ret < 0)
- goto error;
-
-have_folio:
- ret = folio_wait_fscache_killable(folio);
- if (ret < 0)
- goto error;
-have_folio_no_wait:
- *_folio = folio;
- _leave(" = 0");
- return 0;
-
-error_put:
- netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
-error:
- folio_unlock(folio);
- folio_put(folio);
- _leave(" = %d", ret);
- return ret;
-}
-EXPORT_SYMBOL(netfs_write_begin);
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