netfs: Add support for caching single monolithic objects such as AFS dirs

Add support for caching the content of a file that contains a single
monolithic object that must be read/written with a single I/O operation,
such as an AFS directory.

Signed-off-by: David Howells <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
cc: Jeff Layton <[email protected]>
cc: Marc Dionne <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: dhowells

fs/netfs/Makefile

@@ -13,6 +13,7 @@ netfs-y := \
 	read_collect.o \
 	read_pgpriv2.o \
 	read_retry.o \
+	read_single.o \
 	rolling_buffer.o \
 	write_collect.o \
 	write_issue.o \

fs/netfs/buffered_read.c

@@ -137,14 +137,17 @@ static enum netfs_io_source netfs_cache_prepare_read(struct netfs_io_request *rr
 						     loff_t i_size)
 {
 	struct netfs_cache_resources *cres = &rreq->cache_resources;
+	enum netfs_io_source source;
 
 	if (!cres->ops)
 		return NETFS_DOWNLOAD_FROM_SERVER;
-	return cres->ops->prepare_read(subreq, i_size);
+	source = cres->ops->prepare_read(subreq, i_size);
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+	return source;
+
 }
 
-static void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error,
-					bool was_async)
+void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error, bool was_async)
 {
 	struct netfs_io_subrequest *subreq = priv;
 
@@ -213,6 +216,8 @@ static void netfs_read_to_pagecache(struct netfs_io_request *rreq)
 			unsigned long long zp = umin(ictx->zero_point, rreq->i_size);
 			size_t len = subreq->len;
 
+			if (unlikely(rreq->origin == NETFS_READ_SINGLE))
+				zp = rreq->i_size;
 			if (subreq->start >= zp) {
 				subreq->source = source = NETFS_FILL_WITH_ZEROES;
 				goto fill_with_zeroes;

fs/netfs/internal.h

@@ -23,6 +23,7 @@
 /*
  * buffered_read.c
  */
+void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error, bool was_async);
 int netfs_prefetch_for_write(struct file *file, struct folio *folio,
 			     size_t offset, size_t len);
 
@@ -110,6 +111,7 @@ void netfs_unlock_abandoned_read_pages(struct netfs_io_request *rreq);
 extern atomic_t netfs_n_rh_dio_read;
 extern atomic_t netfs_n_rh_readahead;
 extern atomic_t netfs_n_rh_read_folio;
+extern atomic_t netfs_n_rh_read_single;
 extern atomic_t netfs_n_rh_rreq;
 extern atomic_t netfs_n_rh_sreq;
 extern atomic_t netfs_n_rh_download;

fs/netfs/main.c

@@ -37,9 +37,11 @@ static const char *netfs_origins[nr__netfs_io_origin] = {
 	[NETFS_READAHEAD]		= "RA",
 	[NETFS_READPAGE]		= "RP",
 	[NETFS_READ_GAPS]		= "RG",
+	[NETFS_READ_SINGLE]		= "R1",
 	[NETFS_READ_FOR_WRITE]		= "RW",
 	[NETFS_DIO_READ]		= "DR",
 	[NETFS_WRITEBACK]		= "WB",
+	[NETFS_WRITEBACK_SINGLE]	= "W1",
 	[NETFS_WRITETHROUGH]		= "WT",
 	[NETFS_UNBUFFERED_WRITE]	= "UW",
 	[NETFS_DIO_WRITE]		= "DW",

fs/netfs/objects.c

@@ -54,6 +54,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	if (origin == NETFS_READAHEAD ||
 	    origin == NETFS_READPAGE ||
 	    origin == NETFS_READ_GAPS ||
+	    origin == NETFS_READ_SINGLE ||
 	    origin == NETFS_READ_FOR_WRITE ||
 	    origin == NETFS_DIO_READ)
 		INIT_WORK(&rreq->work, NULL);
@@ -196,6 +197,7 @@ struct netfs_io_subrequest *netfs_alloc_subrequest(struct netfs_io_request *rreq
 	case NETFS_READAHEAD:
 	case NETFS_READPAGE:
 	case NETFS_READ_GAPS:
+	case NETFS_READ_SINGLE:
 	case NETFS_READ_FOR_WRITE:
 	case NETFS_DIO_READ:
 		INIT_WORK(&subreq->work, netfs_read_subreq_termination_worker);

fs/netfs/read_collect.c

@@ -361,6 +361,39 @@ static void netfs_rreq_assess_dio(struct netfs_io_request *rreq)
 		inode_dio_end(rreq->inode);
 }
 
+/*
+ * Do processing after reading a monolithic single object.
+ */
+static void netfs_rreq_assess_single(struct netfs_io_request *rreq)
+{
+	struct netfs_io_subrequest *subreq;
+	struct netfs_io_stream *stream = &rreq->io_streams[0];
+
+	subreq = list_first_entry_or_null(&stream->subrequests,
+					  struct netfs_io_subrequest, rreq_link);
+	if (subreq) {
+		if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
+			rreq->error = subreq->error;
+		else
+			rreq->transferred = subreq->transferred;
+
+		if (!rreq->error && subreq->source == NETFS_DOWNLOAD_FROM_SERVER &&
+		    fscache_resources_valid(&rreq->cache_resources)) {
+			trace_netfs_rreq(rreq, netfs_rreq_trace_dirty);
+			netfs_single_mark_inode_dirty(rreq->inode);
+		}
+	}
+
+	if (rreq->iocb) {
+		rreq->iocb->ki_pos += rreq->transferred;
+		if (rreq->iocb->ki_complete)
+			rreq->iocb->ki_complete(
+				rreq->iocb, rreq->error ? rreq->error : rreq->transferred);
+	}
+	if (rreq->netfs_ops->done)
+		rreq->netfs_ops->done(rreq);
+}
+
 /*
  * Assess the state of a read request and decide what to do next.
  *
@@ -378,9 +411,17 @@ void netfs_rreq_terminated(struct netfs_io_request *rreq)
 		return;
 	}
 
-	if (rreq->origin == NETFS_DIO_READ ||
-	    rreq->origin == NETFS_READ_GAPS)
+	switch (rreq->origin) {
+	case NETFS_DIO_READ:
+	case NETFS_READ_GAPS:
 		netfs_rreq_assess_dio(rreq);
+		break;
+	case NETFS_READ_SINGLE:
+		netfs_rreq_assess_single(rreq);
+		break;
+	default:
+		break;
+	}
 	task_io_account_read(rreq->transferred);
 
 	trace_netfs_rreq(rreq, netfs_rreq_trace_wake_ip);

fs/netfs/read_single.c

@@ -0,0 +1,202 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Single, monolithic object support (e.g. AFS directory).
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([email protected])
+ */
+
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/slab.h>
+#include <linux/uio.h>
+#include <linux/sched/mm.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/netfs.h>
+#include "internal.h"
+
+/**
+ * netfs_single_mark_inode_dirty - Mark a single, monolithic object inode dirty
+ * @inode: The inode to mark
+ *
+ * Mark an inode that contains a single, monolithic object as dirty so that its
+ * writepages op will get called.  If set, the SINGLE_NO_UPLOAD flag indicates
+ * that the object will only be written to the cache and not uploaded (e.g. AFS
+ * directory contents).
+ */
+void netfs_single_mark_inode_dirty(struct inode *inode)
+{
+	struct netfs_inode *ictx = netfs_inode(inode);
+	bool cache_only = test_bit(NETFS_ICTX_SINGLE_NO_UPLOAD, &ictx->flags);
+	bool caching = fscache_cookie_enabled(netfs_i_cookie(netfs_inode(inode)));
+
+	if (cache_only && !caching)
+		return;
+
+	mark_inode_dirty(inode);
+
+	if (caching && !(inode->i_state & I_PINNING_NETFS_WB)) {
+		bool need_use = false;
+
+		spin_lock(&inode->i_lock);
+		if (!(inode->i_state & I_PINNING_NETFS_WB)) {
+			inode->i_state |= I_PINNING_NETFS_WB;
+			need_use = true;
+		}
+		spin_unlock(&inode->i_lock);
+
+		if (need_use)
+			fscache_use_cookie(netfs_i_cookie(ictx), true);
+	}
+
+}
+EXPORT_SYMBOL(netfs_single_mark_inode_dirty);
+
+static int netfs_single_begin_cache_read(struct netfs_io_request *rreq, struct netfs_inode *ctx)
+{
+	return fscache_begin_read_operation(&rreq->cache_resources, netfs_i_cookie(ctx));
+}
+
+static void netfs_single_cache_prepare_read(struct netfs_io_request *rreq,
+					    struct netfs_io_subrequest *subreq)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+	if (!cres->ops) {
+		subreq->source = NETFS_DOWNLOAD_FROM_SERVER;
+		return;
+	}
+	subreq->source = cres->ops->prepare_read(subreq, rreq->i_size);
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+
+}
+
+static void netfs_single_read_cache(struct netfs_io_request *rreq,
+				    struct netfs_io_subrequest *subreq)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+	netfs_stat(&netfs_n_rh_read);
+	cres->ops->read(cres, subreq->start, &subreq->io_iter, NETFS_READ_HOLE_FAIL,
+			netfs_cache_read_terminated, subreq);
+}
+
+/*
+ * Perform a read to a buffer from the cache or the server.  Only a single
+ * subreq is permitted as the object must be fetched in a single transaction.
+ */
+static int netfs_single_dispatch_read(struct netfs_io_request *rreq)
+{
+	struct netfs_io_subrequest *subreq;
+	int ret = 0;
+
+	atomic_set(&rreq->nr_outstanding, 1);
+
+	subreq = netfs_alloc_subrequest(rreq);
+	if (!subreq) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	subreq->source	= NETFS_DOWNLOAD_FROM_SERVER;
+	subreq->start	= 0;
+	subreq->len	= rreq->len;
+	subreq->io_iter	= rreq->buffer.iter;
+
+	atomic_inc(&rreq->nr_outstanding);
+
+	spin_lock_bh(&rreq->lock);
+	list_add_tail(&subreq->rreq_link, &rreq->subrequests);
+	trace_netfs_sreq(subreq, netfs_sreq_trace_added);
+	spin_unlock_bh(&rreq->lock);
+
+	netfs_single_cache_prepare_read(rreq, subreq);
+	switch (subreq->source) {
+	case NETFS_DOWNLOAD_FROM_SERVER:
+		netfs_stat(&netfs_n_rh_download);
+		if (rreq->netfs_ops->prepare_read) {
+			ret = rreq->netfs_ops->prepare_read(subreq);
+			if (ret < 0)
+				goto cancel;
+		}
+
+		rreq->netfs_ops->issue_read(subreq);
+		rreq->submitted += subreq->len;
+		break;
+	case NETFS_READ_FROM_CACHE:
+		trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+		netfs_single_read_cache(rreq, subreq);
+		rreq->submitted += subreq->len;
+		ret = 0;
+		break;
+	default:
+		pr_warn("Unexpected single-read source %u\n", subreq->source);
+		WARN_ON_ONCE(true);
+		ret = -EIO;
+		break;
+	}
+
+out:
+	if (atomic_dec_and_test(&rreq->nr_outstanding))
+		netfs_rreq_terminated(rreq);
+	return ret;
+cancel:
+	atomic_dec(&rreq->nr_outstanding);
+	netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_cancel);
+	goto out;
+}
+
+/**
+ * netfs_read_single - Synchronously read a single blob of pages.
+ * @inode: The inode to read from.
+ * @file: The file we're using to read or NULL.
+ * @iter: The buffer we're reading into.
+ *
+ * Fulfil a read request for a single monolithic object by drawing data from
+ * the cache if possible, or the netfs if not.  The buffer may be larger than
+ * the file content; unused beyond the EOF will be zero-filled.  The content
+ * will be read with a single I/O request (though this may 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.  If caching is enabled,
+ * the data will be stored as a single object into the cache.
+ */
+ssize_t netfs_read_single(struct inode *inode, struct file *file, struct iov_iter *iter)
+{
+	struct netfs_io_request *rreq;
+	struct netfs_inode *ictx = netfs_inode(inode);
+	ssize_t ret;
+
+	rreq = netfs_alloc_request(inode->i_mapping, file, 0, iov_iter_count(iter),
+				   NETFS_READ_SINGLE);
+	if (IS_ERR(rreq))
+		return PTR_ERR(rreq);
+
+	ret = netfs_single_begin_cache_read(rreq, ictx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto cleanup_free;
+
+	netfs_stat(&netfs_n_rh_read_single);
+	trace_netfs_read(rreq, 0, rreq->len, netfs_read_trace_read_single);
+
+	rreq->buffer.iter = *iter;
+	netfs_single_dispatch_read(rreq);
+
+	trace_netfs_rreq(rreq, netfs_rreq_trace_wait_ip);
+	wait_on_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS,
+		    TASK_UNINTERRUPTIBLE);
+
+	ret = rreq->error;
+	if (ret == 0)
+		ret = rreq->transferred;
+	netfs_put_request(rreq, true, netfs_rreq_trace_put_return);
+	return ret;
+
+cleanup_free:
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_read_single);

fs/netfs/stats.c

@@ -12,6 +12,7 @@
 atomic_t netfs_n_rh_dio_read;
 atomic_t netfs_n_rh_readahead;
 atomic_t netfs_n_rh_read_folio;
+atomic_t netfs_n_rh_read_single;
 atomic_t netfs_n_rh_rreq;
 atomic_t netfs_n_rh_sreq;
 atomic_t netfs_n_rh_download;
@@ -46,10 +47,11 @@ atomic_t netfs_n_folioq;
 
 int netfs_stats_show(struct seq_file *m, void *v)
 {
-	seq_printf(m, "Reads  : DR=%u RA=%u RF=%u WB=%u WBZ=%u\n",
+	seq_printf(m, "Reads  : DR=%u RA=%u RF=%u RS=%u WB=%u WBZ=%u\n",
 		   atomic_read(&netfs_n_rh_dio_read),
 		   atomic_read(&netfs_n_rh_readahead),
 		   atomic_read(&netfs_n_rh_read_folio),
+		   atomic_read(&netfs_n_rh_read_single),
 		   atomic_read(&netfs_n_rh_write_begin),
 		   atomic_read(&netfs_n_rh_write_zskip));
 	seq_printf(m, "Writes : BW=%u WT=%u DW=%u WP=%u 2C=%u\n",

fs/netfs/write_collect.c

@@ -17,7 +17,7 @@
 #define HIT_PENDING		0x01	/* A front op was still pending */
 #define NEED_REASSESS		0x02	/* Need to loop round and reassess */
 #define MADE_PROGRESS		0x04	/* Made progress cleaning up a stream or the folio set */
-#define BUFFERED		0x08	/* The pagecache needs cleaning up */
+#define NEED_UNLOCK		0x08	/* The pagecache needs unlocking */
 #define NEED_RETRY		0x10	/* A front op requests retrying */
 #define SAW_FAILURE		0x20	/* One stream or hit a permanent failure */
 
@@ -179,7 +179,7 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 	if (wreq->origin == NETFS_WRITEBACK ||
 	    wreq->origin == NETFS_WRITETHROUGH ||
 	    wreq->origin == NETFS_PGPRIV2_COPY_TO_CACHE)
-		notes = BUFFERED;
+		notes = NEED_UNLOCK;
 	else
 		notes = 0;
 
@@ -276,7 +276,7 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 	trace_netfs_collect_state(wreq, wreq->collected_to, notes);
 
 	/* Unlock any folios that we have now finished with. */
-	if (notes & BUFFERED) {
+	if (notes & NEED_UNLOCK) {
 		if (wreq->cleaned_to < wreq->collected_to)
 			netfs_writeback_unlock_folios(wreq, &notes);
 	} else {