kernel

linux-6.8.1/fs/netfs/buffered_read.c

@@ -0,0 +1,633 @@
+// 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@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 netfs_folio *finfo;
+	struct folio *folio;
+	pgoff_t start_page = rreq->start / PAGE_SIZE;
+	pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
+	size_t account = 0;
+	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);
+	subreq_failed = (subreq->error < 0);
+
+	trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
+
+	rcu_read_lock();
+	xas_for_each(&xas, folio, last_page) {
+		loff_t pg_end;
+		bool pg_failed = false;
+		bool folio_started;
+
+		if (xas_retry(&xas, folio))
+			continue;
+
+		pg_end = folio_pos(folio) + folio_size(folio) - 1;
+
+		folio_started = false;
+		for (;;) {
+			loff_t sreq_end;
+
+			if (!subreq) {
+				pg_failed = true;
+				break;
+			}
+			if (!folio_started && test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
+				trace_netfs_folio(folio, netfs_folio_trace_copy_to_cache);
+				folio_start_fscache(folio);
+				folio_started = true;
+			}
+			pg_failed |= subreq_failed;
+			sreq_end = subreq->start + subreq->len - 1;
+			if (pg_end < sreq_end)
+				break;
+
+			account += subreq->transferred;
+			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 (pg_end == sreq_end)
+				break;
+		}
+
+		if (!pg_failed) {
+			flush_dcache_folio(folio);
+			finfo = netfs_folio_info(folio);
+			if (finfo) {
+				trace_netfs_folio(folio, netfs_folio_trace_filled_gaps);
+				if (finfo->netfs_group)
+					folio_change_private(folio, finfo->netfs_group);
+				else
+					folio_detach_private(folio);
+				kfree(finfo);
+			}
+			folio_mark_uptodate(folio);
+		}
+
+		if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
+			if (folio->index == 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);
+	}
+}
+
+/*
+ * Begin an operation, and fetch the stored zero point value from the cookie if
+ * available.
+ */
+static int netfs_begin_cache_read(struct netfs_io_request *rreq, struct netfs_inode *ctx)
+{
+	return fscache_begin_read_operation(&rreq->cache_resources, netfs_i_cookie(ctx));
+}
+
+/**
+ * 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_inode *ctx = netfs_inode(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;
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	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);
+
+	/* Set up the output buffer */
+	iov_iter_xarray(&rreq->iter, ITER_DEST, &ractl->mapping->i_pages,
+			rreq->start, rreq->len);
+
+	/* 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);
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+	return;
+
+cleanup_free:
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
+	return;
+}
+EXPORT_SYMBOL(netfs_readahead);
+
+/**
+ * netfs_read_folio - Helper to manage a read_folio request
+ * @file: The file to read from
+ * @folio: The folio to read
+ *
+ * Fulfil a read_folio 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_read_folio(struct file *file, struct folio *folio)
+{
+	struct address_space *mapping = folio->mapping;
+	struct netfs_io_request *rreq;
+	struct netfs_inode *ctx = netfs_inode(mapping->host);
+	struct folio *sink = NULL;
+	int ret;
+
+	_enter("%lx", folio->index);
+
+	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;
+	}
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	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);
+
+	/* Set up the output buffer */
+	if (folio_test_dirty(folio)) {
+		/* Handle someone trying to read from an unflushed streaming
+		 * write.  We fiddle the buffer so that a gap at the beginning
+		 * and/or a gap at the end get copied to, but the middle is
+		 * discarded.
+		 */
+		struct netfs_folio *finfo = netfs_folio_info(folio);
+		struct bio_vec *bvec;
+		unsigned int from = finfo->dirty_offset;
+		unsigned int to = from + finfo->dirty_len;
+		unsigned int off = 0, i = 0;
+		size_t flen = folio_size(folio);
+		size_t nr_bvec = flen / PAGE_SIZE + 2;
+		size_t part;
+
+		ret = -ENOMEM;
+		bvec = kmalloc_array(nr_bvec, sizeof(*bvec), GFP_KERNEL);
+		if (!bvec)
+			goto discard;
+
+		sink = folio_alloc(GFP_KERNEL, 0);
+		if (!sink)
+			goto discard;
+
+		trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
+
+		rreq->direct_bv = bvec;
+		rreq->direct_bv_count = nr_bvec;
+		if (from > 0) {
+			bvec_set_folio(&bvec[i++], folio, from, 0);
+			off = from;
+		}
+		while (off < to) {
+			part = min_t(size_t, to - off, PAGE_SIZE);
+			bvec_set_folio(&bvec[i++], sink, part, 0);
+			off += part;
+		}
+		if (to < flen)
+			bvec_set_folio(&bvec[i++], folio, flen - to, to);
+		iov_iter_bvec(&rreq->iter, ITER_DEST, bvec, i, rreq->len);
+	} else {
+		iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
+				rreq->start, rreq->len);
+	}
+
+	ret = netfs_begin_read(rreq, true);
+	if (sink)
+		folio_put(sink);
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+	return ret < 0 ? ret : 0;
+
+discard:
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
+alloc_error:
+	folio_unlock(folio);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_read_folio);
+
+/*
+ * 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, plen);
+	return true;
+}
+
+/**
+ * netfs_write_begin - Helper to prepare for writing
+ * @ctx: The netfs context
+ * @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)
+ * @_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 or it may return an error.  It may also unlock and put the
+ * folio, provided it sets ``*foliop`` to NULL, in which case a return of 0
+ * will cause the folio to be re-got and the process to be retried.
+ *
+ * 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 netfs_inode *ctx,
+		      struct file *file, struct address_space *mapping,
+		      loff_t pos, unsigned int len, struct folio **_folio,
+		      void **_fsdata)
+{
+	struct netfs_io_request *rreq;
+	struct folio *folio;
+	pgoff_t index = pos >> PAGE_SHIFT;
+	int ret;
+
+	DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
+
+retry:
+	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
+				    mapping_gfp_mask(mapping));
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
+
+	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);
+			goto error;
+		}
+		if (!folio)
+			goto retry;
+	}
+
+	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;
+	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	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);
+
+	/* Set up the output buffer */
+	iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
+			rreq->start, rreq->len);
+
+	/* 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;
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+
+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:
+	if (folio) {
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+	_leave(" = %d", ret);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_write_begin);
+
+/*
+ * Preload the data into a page we're proposing to write into.
+ */
+int netfs_prefetch_for_write(struct file *file, struct folio *folio,
+			     size_t offset, size_t len)
+{
+	struct netfs_io_request *rreq;
+	struct address_space *mapping = folio->mapping;
+	struct netfs_inode *ctx = netfs_inode(mapping->host);
+	unsigned long long start = folio_pos(folio);
+	size_t flen = folio_size(folio);
+	int ret;
+
+	_enter("%zx @%llx", flen, start);
+
+	ret = -ENOMEM;
+
+	rreq = netfs_alloc_request(mapping, file, start, flen,
+				   NETFS_READ_FOR_WRITE);
+	if (IS_ERR(rreq)) {
+		ret = PTR_ERR(rreq);
+		goto error;
+	}
+
+	rreq->no_unlock_folio = folio->index;
+	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
+	ret = netfs_begin_cache_read(rreq, ctx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto error_put;
+
+	netfs_stat(&netfs_n_rh_write_begin);
+	trace_netfs_read(rreq, start, flen, netfs_read_trace_prefetch_for_write);
+
+	/* Set up the output buffer */
+	iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
+			rreq->start, rreq->len);
+
+	ret = netfs_begin_read(rreq, true);
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+	return ret;
+
+error_put:
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
+error:
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/**
+ * netfs_buffered_read_iter - Filesystem buffered I/O read routine
+ * @iocb: kernel I/O control block
+ * @iter: destination for the data read
+ *
+ * This is the ->read_iter() routine for all filesystems that can use the page
+ * cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall be
+ * returned when no data can be read without waiting for I/O requests to
+ * complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O requests
+ * shall be made for the read or for readahead.  When no data can be read,
+ * -EAGAIN shall be returned.  When readahead would be triggered, a partial,
+ * possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t netfs_buffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	struct netfs_inode *ictx = netfs_inode(inode);
+	ssize_t ret;
+
+	if (WARN_ON_ONCE((iocb->ki_flags & IOCB_DIRECT) ||
+			 test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags)))
+		return -EINVAL;
+
+	ret = netfs_start_io_read(inode);
+	if (ret == 0) {
+		ret = filemap_read(iocb, iter, 0);
+		netfs_end_io_read(inode);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(netfs_buffered_read_iter);
+
+/**
+ * netfs_file_read_iter - Generic filesystem read routine
+ * @iocb: kernel I/O control block
+ * @iter: destination for the data read
+ *
+ * This is the ->read_iter() routine for all filesystems that can use the page
+ * cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall be
+ * returned when no data can be read without waiting for I/O requests to
+ * complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O requests
+ * shall be made for the read or for readahead.  When no data can be read,
+ * -EAGAIN shall be returned.  When readahead would be triggered, a partial,
+ * possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t netfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct netfs_inode *ictx = netfs_inode(iocb->ki_filp->f_mapping->host);
+
+	if ((iocb->ki_flags & IOCB_DIRECT) ||
+	    test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags))
+		return netfs_unbuffered_read_iter(iocb, iter);
+
+	return netfs_buffered_read_iter(iocb, iter);
+}
+EXPORT_SYMBOL(netfs_file_read_iter);