Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted

Pull networking updates from Jakub Kicinski:
 "Core:

   - Add dedicated kmem_cache for typical/small skb->head, avoid having
     to access struct page at kfree time, and improve memory use.

   - Introduce sysctl to set default RPS configuration for new netdevs.

   - Define Netlink protocol specification format which can be used to
     describe messages used by each family and auto-generate parsers.
     Add tools for generating kernel data structures and uAPI headers.

   - Expose all net/core sysctls inside netns.

   - Remove 4s sleep in netpoll if carrier is instantly detected on
     boot.

   - Add configurable limit of MDB entries per port, and port-vlan.

   - Continue populating drop reasons throughout the stack.

   - Retire a handful of legacy Qdiscs and classifiers.

  Protocols:

   - Support IPv4 big TCP (TSO frames larger than 64kB).

   - Add IP_LOCAL_PORT_RANGE socket option, to control local port range
     on socket by socket basis.

   - Track and report in procfs number of MPTCP sockets used.

   - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path
     manager.

   - IPv6: don't check net.ipv6.route.max_size and rely on garbage
     collection to free memory (similarly to IPv4).

   - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986).

   - ICMP: add per-rate limit counters.

   - Add support for user scanning requests in ieee802154.

   - Remove static WEP support.

   - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate
     reporting.

   - WiFi 7 EHT channel puncturing support (client & AP).

  BPF:

   - Add a rbtree data structure following the "next-gen data structure"
     precedent set by recently added linked list, that is, by using
     kfunc + kptr instead of adding a new BPF map type.

   - Expose XDP hints via kfuncs with initial support for RX hash and
     timestamp metadata.

   - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to
     better support decap on GRE tunnel devices not operating in collect
     metadata.

   - Improve x86 JIT's codegen for PROBE_MEM runtime error checks.

   - Remove the need for trace_printk_lock for bpf_trace_printk and
     bpf_trace_vprintk helpers.

   - Extend libbpf's bpf_tracing.h support for tracing arguments of
     kprobes/uprobes and syscall as a special case.

   - Significantly reduce the search time for module symbols by
     livepatch and BPF.

   - Enable cpumasks to be used as kptrs, which is useful for tracing
     programs tracking which tasks end up running on which CPUs in
     different time intervals.

   - Add support for BPF trampoline on s390x and riscv64.

   - Add capability to export the XDP features supported by the NIC.

   - Add __bpf_kfunc tag for marking kernel functions as kfuncs.

   - Add cgroup.memory=nobpf kernel parameter option to disable BPF
     memory accounting for container environments.

  Netfilter:

   - Remove the CLUSTERIP target. It has been marked as obsolete for
     years, and we still have WARN splats wrt races of the out-of-band
     /proc interface installed by this target.

   - Add 'destroy' commands to nf_tables. They are identical to the
     existing 'delete' commands, but do not return an error if the
     referenced object (set, chain, rule...) did not exist.

  Driver API:

   - Improve cpumask_local_spread() locality to help NICs set the right
     IRQ affinity on AMD platforms.

   - Separate C22 and C45 MDIO bus transactions more clearly.

   - Introduce new DCB table to control DSCP rewrite on egress.

   - Support configuration of Physical Layer Collision Avoidance (PLCA)
     Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of
     shared medium Ethernet.

   - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing
     preemption of low priority frames by high priority frames.

   - Add support for controlling MACSec offload using netlink SET.

   - Rework devlink instance refcounts to allow registration and
     de-registration under the instance lock. Split the code into
     multiple files, drop some of the unnecessarily granular locks and
     factor out common parts of netlink operation handling.

   - Add TX frame aggregation parameters (for USB drivers).

   - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning
     messages with notifications for debug.

   - Allow offloading of UDP NEW connections via act_ct.

   - Add support for per action HW stats in TC.

   - Support hardware miss to TC action (continue processing in SW from
     a specific point in the action chain).

   - Warn if old Wireless Extension user space interface is used with
     modern cfg80211/mac80211 drivers. Do not support Wireless
     Extensions for Wi-Fi 7 devices at all. Everyone should switch to
     using nl80211 interface instead.

   - Improve the CAN bit timing configuration. Use extack to return
     error messages directly to user space, update the SJW handling,
     including the definition of a new default value that will benefit
     CAN-FD controllers, by increasing their oscillator tolerance.

  New hardware / drivers:

   - Ethernet:
      - nVidia BlueField-3 support (control traffic driver)
      - Ethernet support for imx93 SoCs
      - Motorcomm yt8531 gigabit Ethernet PHY
      - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA)
      - Microchip LAN8841 PHY (incl. cable diagnostics and PTP)
      - Amlogic gxl MDIO mux

   - WiFi:
      - RealTek RTL8188EU (rtl8xxxu)
      - Qualcomm Wi-Fi 7 devices (ath12k)

   - CAN:
      - Renesas R-Car V4H

  Drivers:

   - Bluetooth:
      - Set Per Platform Antenna Gain (PPAG) for Intel controllers.

   - Ethernet NICs:
      - Intel (1G, igc):
         - support TSN / Qbv / packet scheduling features of i226 model
      - Intel (100G, ice):
         - use GNSS subsystem instead of TTY
         - multi-buffer XDP support
         - extend support for GPIO pins to E823 devices
      - nVidia/Mellanox:
         - update the shared buffer configuration on PFC commands
         - implement PTP adjphase function for HW offset control
         - TC support for Geneve and GRE with VF tunnel offload
         - more efficient crypto key management method
         - multi-port eswitch support
      - Netronome/Corigine:
         - add DCB IEEE support
         - support IPsec offloading for NFP3800
      - Freescale/NXP (enetc):
         - support XDP_REDIRECT for XDP non-linear buffers
         - improve reconfig, avoid link flap and waiting for idle
         - support MAC Merge layer
      - Other NICs:
         - sfc/ef100: add basic devlink support for ef100
         - ionic: rx_push mode operation (writing descriptors via MMIO)
         - bnxt: use the auxiliary bus abstraction for RDMA
         - r8169: disable ASPM and reset bus in case of tx timeout
         - cpsw: support QSGMII mode for J721e CPSW9G
         - cpts: support pulse-per-second output
         - ngbe: add an mdio bus driver
         - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing
         - r8152: handle devices with FW with NCM support
         - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation
         - virtio-net: support multi buffer XDP
         - virtio/vsock: replace virtio_vsock_pkt with sk_buff
         - tsnep: XDP support

   - Ethernet high-speed switches:
      - nVidia/Mellanox (mlxsw):
         - add support for latency TLV (in FW control messages)
      - Microchip (sparx5):
         - separate explicit and implicit traffic forwarding rules, make
           the implicit rules always active
         - add support for egress DSCP rewrite
         - IS0 VCAP support (Ingress Classification)
         - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS
           etc.)
         - ES2 VCAP support (Egress Access Control)
         - support for Per-Stream Filtering and Policing (802.1Q,
           8.6.5.1)

   - Ethernet embedded switches:
      - Marvell (mv88e6xxx):
         - add MAB (port auth) offload support
         - enable PTP receive for mv88e6390
      - NXP (ocelot):
         - support MAC Merge layer
         - support for the the vsc7512 internal copper phys
      - Microchip:
         - lan9303: convert to PHYLINK
         - lan966x: support TC flower filter statistics
         - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x
         - lan937x: support Credit Based Shaper configuration
         - ksz9477: support Energy Efficient Ethernet
      - other:
         - qca8k: convert to regmap read/write API, use bulk operations
         - rswitch: Improve TX timestamp accuracy

   - Intel WiFi (iwlwifi):
      - EHT (Wi-Fi 7) rate reporting
      - STEP equalizer support: transfer some STEP (connection to radio
        on platforms with integrated wifi) related parameters from the
        BIOS to the firmware.

   - Qualcomm 802.11ax WiFi (ath11k):
      - IPQ5018 support
      - Fine Timing Measurement (FTM) responder role support
      - channel 177 support

   - MediaTek WiFi (mt76):
      - per-PHY LED support
      - mt7996: EHT (Wi-Fi 7) support
      - Wireless Ethernet Dispatch (WED) reset support
      - switch to using page pool allocator

   - RealTek WiFi (rtw89):
      - support new version of Bluetooth co-existance

   - Mobile:
      - rmnet: support TX aggregation"

* tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits)
  page_pool: add a comment explaining the fragment counter usage
  net: ethtool: fix __ethtool_dev_mm_supported() implementation
  ethtool: pse-pd: Fix double word in comments
  xsk: add linux/vmalloc.h to xsk.c
  sefltests: netdevsim: wait for devlink instance after netns removal
  selftest: fib_tests: Always cleanup before exit
  net/mlx5e: Align IPsec ASO result memory to be as required by hardware
  net/mlx5e: TC, Set CT miss to the specific ct action instance
  net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
  net/mlx5: Refactor tc miss handling to a single function
  net/mlx5: Kconfig: Make tc offload depend on tc skb extension
  net/sched: flower: Support hardware miss to tc action
  net/sched: flower: Move filter handle initialization earlier
  net/sched: cls_api: Support hardware miss to tc action
  net/sched: Rename user cookie and act cookie
  sfc: fix builds without CONFIG_RTC_LIB
  sfc: clean up some inconsistent indentings
  net/mlx4_en: Introduce flexible array to silence overflow warning
  net: lan966x: Fix possible deadlock inside PTP
  net/ulp: Remove redundant ->clone() test in inet_clone_ulp().
  ...

1 files changed, 672 insertions, 0 deletions

diff --git a/fs/mpage.c b/fs/mpage.c
new file mode 100644
index 000000000..ce5317942
--- /dev/null
+++ b/fs/mpage.c
@@ -0,0 +1,672 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/mpage.c
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ *
+ * Contains functions related to preparing and submitting BIOs which contain
+ * multiple pagecache pages.
+ *
+ * 15May2002	Andrew Morton
+ *		Initial version
+ * 27Jun2002	axboe@suse.de
+ *		use bio_add_page() to build bio's just the right size
+ */
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/kdev_t.h>
+#include <linux/gfp.h>
+#include <linux/bio.h>
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include <linux/blkdev.h>
+#include <linux/highmem.h>
+#include <linux/prefetch.h>
+#include <linux/mpage.h>
+#include <linux/mm_inline.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+#include "internal.h"
+
+/*
+ * I/O completion handler for multipage BIOs.
+ *
+ * The mpage code never puts partial pages into a BIO (except for end-of-file).
+ * If a page does not map to a contiguous run of blocks then it simply falls
+ * back to block_read_full_folio().
+ *
+ * Why is this?  If a page's completion depends on a number of different BIOs
+ * which can complete in any order (or at the same time) then determining the
+ * status of that page is hard.  See end_buffer_async_read() for the details.
+ * There is no point in duplicating all that complexity.
+ */
+static void mpage_end_io(struct bio *bio)
+{
+	struct bio_vec *bv;
+	struct bvec_iter_all iter_all;
+
+	bio_for_each_segment_all(bv, bio, iter_all) {
+		struct page *page = bv->bv_page;
+		page_endio(page, bio_op(bio),
+			   blk_status_to_errno(bio->bi_status));
+	}
+
+	bio_put(bio);
+}
+
+static struct bio *mpage_bio_submit(struct bio *bio)
+{
+	bio->bi_end_io = mpage_end_io;
+	guard_bio_eod(bio);
+	submit_bio(bio);
+	return NULL;
+}
+
+/*
+ * support function for mpage_readahead.  The fs supplied get_block might
+ * return an up to date buffer.  This is used to map that buffer into
+ * the page, which allows read_folio to avoid triggering a duplicate call
+ * to get_block.
+ *
+ * The idea is to avoid adding buffers to pages that don't already have
+ * them.  So when the buffer is up to date and the page size == block size,
+ * this marks the page up to date instead of adding new buffers.
+ */
+static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
+		int page_block)
+{
+	struct inode *inode = folio->mapping->host;
+	struct buffer_head *page_bh, *head;
+	int block = 0;
+
+	head = folio_buffers(folio);
+	if (!head) {
+		/*
+		 * don't make any buffers if there is only one buffer on
+		 * the folio and the folio just needs to be set up to date
+		 */
+		if (inode->i_blkbits == PAGE_SHIFT &&
+		    buffer_uptodate(bh)) {
+			folio_mark_uptodate(folio);
+			return;
+		}
+		create_empty_buffers(&folio->page, i_blocksize(inode), 0);
+		head = folio_buffers(folio);
+	}
+
+	page_bh = head;
+	do {
+		if (block == page_block) {
+			page_bh->b_state = bh->b_state;
+			page_bh->b_bdev = bh->b_bdev;
+			page_bh->b_blocknr = bh->b_blocknr;
+			break;
+		}
+		page_bh = page_bh->b_this_page;
+		block++;
+	} while (page_bh != head);
+}
+
+struct mpage_readpage_args {
+	struct bio *bio;
+	struct folio *folio;
+	unsigned int nr_pages;
+	bool is_readahead;
+	sector_t last_block_in_bio;
+	struct buffer_head map_bh;
+	unsigned long first_logical_block;
+	get_block_t *get_block;
+};
+
+/*
+ * This is the worker routine which does all the work of mapping the disk
+ * blocks and constructs largest possible bios, submits them for IO if the
+ * blocks are not contiguous on the disk.
+ *
+ * We pass a buffer_head back and forth and use its buffer_mapped() flag to
+ * represent the validity of its disk mapping and to decide when to do the next
+ * get_block() call.
+ */
+static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
+{
+	struct folio *folio = args->folio;
+	struct inode *inode = folio->mapping->host;
+	const unsigned blkbits = inode->i_blkbits;
+	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+	const unsigned blocksize = 1 << blkbits;
+	struct buffer_head *map_bh = &args->map_bh;
+	sector_t block_in_file;
+	sector_t last_block;
+	sector_t last_block_in_file;
+	sector_t blocks[MAX_BUF_PER_PAGE];
+	unsigned page_block;
+	unsigned first_hole = blocks_per_page;
+	struct block_device *bdev = NULL;
+	int length;
+	int fully_mapped = 1;
+	blk_opf_t opf = REQ_OP_READ;
+	unsigned nblocks;
+	unsigned relative_block;
+	gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
+
+	/* MAX_BUF_PER_PAGE, for example */
+	VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
+
+	if (args->is_readahead) {
+		opf |= REQ_RAHEAD;
+		gfp |= __GFP_NORETRY | __GFP_NOWARN;
+	}
+
+	if (folio_buffers(folio))
+		goto confused;
+
+	block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
+	last_block = block_in_file + args->nr_pages * blocks_per_page;
+	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
+	if (last_block > last_block_in_file)
+		last_block = last_block_in_file;
+	page_block = 0;
+
+	/*
+	 * Map blocks using the result from the previous get_blocks call first.
+	 */
+	nblocks = map_bh->b_size >> blkbits;
+	if (buffer_mapped(map_bh) &&
+			block_in_file > args->first_logical_block &&
+			block_in_file < (args->first_logical_block + nblocks)) {
+		unsigned map_offset = block_in_file - args->first_logical_block;
+		unsigned last = nblocks - map_offset;
+
+		for (relative_block = 0; ; relative_block++) {
+			if (relative_block == last) {
+				clear_buffer_mapped(map_bh);
+				break;
+			}
+			if (page_block == blocks_per_page)
+				break;
+			blocks[page_block] = map_bh->b_blocknr + map_offset +
+						relative_block;
+			page_block++;
+			block_in_file++;
+		}
+		bdev = map_bh->b_bdev;
+	}
+
+	/*
+	 * Then do more get_blocks calls until we are done with this folio.
+	 */
+	map_bh->b_page = &folio->page;
+	while (page_block < blocks_per_page) {
+		map_bh->b_state = 0;
+		map_bh->b_size = 0;
+
+		if (block_in_file < last_block) {
+			map_bh->b_size = (last_block-block_in_file) << blkbits;
+			if (args->get_block(inode, block_in_file, map_bh, 0))
+				goto confused;
+			args->first_logical_block = block_in_file;
+		}
+
+		if (!buffer_mapped(map_bh)) {
+			fully_mapped = 0;
+			if (first_hole == blocks_per_page)
+				first_hole = page_block;
+			page_block++;
+			block_in_file++;
+			continue;
+		}
+
+		/* some filesystems will copy data into the page during
+		 * the get_block call, in which case we don't want to
+		 * read it again.  map_buffer_to_folio copies the data
+		 * we just collected from get_block into the folio's buffers
+		 * so read_folio doesn't have to repeat the get_block call
+		 */
+		if (buffer_uptodate(map_bh)) {
+			map_buffer_to_folio(folio, map_bh, page_block);
+			goto confused;
+		}
+	
+		if (first_hole != blocks_per_page)
+			goto confused;		/* hole -> non-hole */
+
+		/* Contiguous blocks? */
+		if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
+			goto confused;
+		nblocks = map_bh->b_size >> blkbits;
+		for (relative_block = 0; ; relative_block++) {
+			if (relative_block == nblocks) {
+				clear_buffer_mapped(map_bh);
+				break;
+			} else if (page_block == blocks_per_page)
+				break;
+			blocks[page_block] = map_bh->b_blocknr+relative_block;
+			page_block++;
+			block_in_file++;
+		}
+		bdev = map_bh->b_bdev;
+	}
+
+	if (first_hole != blocks_per_page) {
+		folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
+		if (first_hole == 0) {
+			folio_mark_uptodate(folio);
+			folio_unlock(folio);
+			goto out;
+		}
+	} else if (fully_mapped) {
+		folio_set_mappedtodisk(folio);
+	}
+
+	/*
+	 * This folio will go to BIO.  Do we need to send this BIO off first?
+	 */
+	if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
+		args->bio = mpage_bio_submit(args->bio);
+
+alloc_new:
+	if (args->bio == NULL) {
+		if (first_hole == blocks_per_page) {
+			if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
+								&folio->page))
+				goto out;
+		}
+		args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), opf,
+				      gfp);
+		if (args->bio == NULL)
+			goto confused;
+		args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+	}
+
+	length = first_hole << blkbits;
+	if (!bio_add_folio(args->bio, folio, length, 0)) {
+		args->bio = mpage_bio_submit(args->bio);
+		goto alloc_new;
+	}
+
+	relative_block = block_in_file - args->first_logical_block;
+	nblocks = map_bh->b_size >> blkbits;
+	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
+	    (first_hole != blocks_per_page))
+		args->bio = mpage_bio_submit(args->bio);
+	else
+		args->last_block_in_bio = blocks[blocks_per_page - 1];
+out:
+	return args->bio;
+
+confused:
+	if (args->bio)
+		args->bio = mpage_bio_submit(args->bio);
+	if (!folio_test_uptodate(folio))
+		block_read_full_folio(folio, args->get_block);
+	else
+		folio_unlock(folio);
+	goto out;
+}
+
+/**
+ * mpage_readahead - start reads against pages
+ * @rac: Describes which pages to read.
+ * @get_block: The filesystem's block mapper function.
+ *
+ * This function walks the pages and the blocks within each page, building and
+ * emitting large BIOs.
+ *
+ * If anything unusual happens, such as:
+ *
+ * - encountering a page which has buffers
+ * - encountering a page which has a non-hole after a hole
+ * - encountering a page with non-contiguous blocks
+ *
+ * then this code just gives up and calls the buffer_head-based read function.
+ * It does handle a page which has holes at the end - that is a common case:
+ * the end-of-file on blocksize < PAGE_SIZE setups.
+ *
+ * BH_Boundary explanation:
+ *
+ * There is a problem.  The mpage read code assembles several pages, gets all
+ * their disk mappings, and then submits them all.  That's fine, but obtaining
+ * the disk mappings may require I/O.  Reads of indirect blocks, for example.
+ *
+ * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
+ * submitted in the following order:
+ *
+ * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
+ *
+ * because the indirect block has to be read to get the mappings of blocks
+ * 13,14,15,16.  Obviously, this impacts performance.
+ *
+ * So what we do it to allow the filesystem's get_block() function to set
+ * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
+ * after this one will require I/O against a block which is probably close to
+ * this one.  So you should push what I/O you have currently accumulated.
+ *
+ * This all causes the disk requests to be issued in the correct order.
+ */
+void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
+{
+	struct folio *folio;
+	struct mpage_readpage_args args = {
+		.get_block = get_block,
+		.is_readahead = true,
+	};
+
+	while ((folio = readahead_folio(rac))) {
+		prefetchw(&folio->flags);
+		args.folio = folio;
+		args.nr_pages = readahead_count(rac);
+		args.bio = do_mpage_readpage(&args);
+	}
+	if (args.bio)
+		mpage_bio_submit(args.bio);
+}
+EXPORT_SYMBOL(mpage_readahead);
+
+/*
+ * This isn't called much at all
+ */
+int mpage_read_folio(struct folio *folio, get_block_t get_block)
+{
+	struct mpage_readpage_args args = {
+		.folio = folio,
+		.nr_pages = 1,
+		.get_block = get_block,
+	};
+
+	args.bio = do_mpage_readpage(&args);
+	if (args.bio)
+		mpage_bio_submit(args.bio);
+	return 0;
+}
+EXPORT_SYMBOL(mpage_read_folio);
+
+/*
+ * Writing is not so simple.
+ *
+ * If the page has buffers then they will be used for obtaining the disk
+ * mapping.  We only support pages which are fully mapped-and-dirty, with a
+ * special case for pages which are unmapped at the end: end-of-file.
+ *
+ * If the page has no buffers (preferred) then the page is mapped here.
+ *
+ * If all blocks are found to be contiguous then the page can go into the
+ * BIO.  Otherwise fall back to the mapping's writepage().
+ * 
+ * FIXME: This code wants an estimate of how many pages are still to be
+ * written, so it can intelligently allocate a suitably-sized BIO.  For now,
+ * just allocate full-size (16-page) BIOs.
+ */
+
+struct mpage_data {
+	struct bio *bio;
+	sector_t last_block_in_bio;
+	get_block_t *get_block;
+};
+
+/*
+ * We have our BIO, so we can now mark the buffers clean.  Make
+ * sure to only clean buffers which we know we'll be writing.
+ */
+static void clean_buffers(struct page *page, unsigned first_unmapped)
+{
+	unsigned buffer_counter = 0;
+	struct buffer_head *bh, *head;
+	if (!page_has_buffers(page))
+		return;
+	head = page_buffers(page);
+	bh = head;
+
+	do {
+		if (buffer_counter++ == first_unmapped)
+			break;
+		clear_buffer_dirty(bh);
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	/*
+	 * we cannot drop the bh if the page is not uptodate or a concurrent
+	 * read_folio would fail to serialize with the bh and it would read from
+	 * disk before we reach the platter.
+	 */
+	if (buffer_heads_over_limit && PageUptodate(page))
+		try_to_free_buffers(page_folio(page));
+}
+
+/*
+ * For situations where we want to clean all buffers attached to a page.
+ * We don't need to calculate how many buffers are attached to the page,
+ * we just need to specify a number larger than the maximum number of buffers.
+ */
+void clean_page_buffers(struct page *page)
+{
+	clean_buffers(page, ~0U);
+}
+
+static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+		      void *data)
+{
+	struct mpage_data *mpd = data;
+	struct bio *bio = mpd->bio;
+	struct address_space *mapping = page->mapping;
+	struct inode *inode = page->mapping->host;
+	const unsigned blkbits = inode->i_blkbits;
+	unsigned long end_index;
+	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+	sector_t last_block;
+	sector_t block_in_file;
+	sector_t blocks[MAX_BUF_PER_PAGE];
+	unsigned page_block;
+	unsigned first_unmapped = blocks_per_page;
+	struct block_device *bdev = NULL;
+	int boundary = 0;
+	sector_t boundary_block = 0;
+	struct block_device *boundary_bdev = NULL;
+	int length;
+	struct buffer_head map_bh;
+	loff_t i_size = i_size_read(inode);
+	int ret = 0;
+
+	if (page_has_buffers(page)) {
+		struct buffer_head *head = page_buffers(page);
+		struct buffer_head *bh = head;
+
+		/* If they're all mapped and dirty, do it */
+		page_block = 0;
+		do {
+			BUG_ON(buffer_locked(bh));
+			if (!buffer_mapped(bh)) {
+				/*
+				 * unmapped dirty buffers are created by
+				 * block_dirty_folio -> mmapped data
+				 */
+				if (buffer_dirty(bh))
+					goto confused;
+				if (first_unmapped == blocks_per_page)
+					first_unmapped = page_block;
+				continue;
+			}
+
+			if (first_unmapped != blocks_per_page)
+				goto confused;	/* hole -> non-hole */
+
+			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
+				goto confused;
+			if (page_block) {
+				if (bh->b_blocknr != blocks[page_block-1] + 1)
+					goto confused;
+			}
+			blocks[page_block++] = bh->b_blocknr;
+			boundary = buffer_boundary(bh);
+			if (boundary) {
+				boundary_block = bh->b_blocknr;
+				boundary_bdev = bh->b_bdev;
+			}
+			bdev = bh->b_bdev;
+		} while ((bh = bh->b_this_page) != head);
+
+		if (first_unmapped)
+			goto page_is_mapped;
+
+		/*
+		 * Page has buffers, but they are all unmapped. The page was
+		 * created by pagein or read over a hole which was handled by
+		 * block_read_full_folio().  If this address_space is also
+		 * using mpage_readahead then this can rarely happen.
+		 */
+		goto confused;
+	}
+
+	/*
+	 * The page has no buffers: map it to disk
+	 */
+	BUG_ON(!PageUptodate(page));
+	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+	last_block = (i_size - 1) >> blkbits;
+	map_bh.b_page = page;
+	for (page_block = 0; page_block < blocks_per_page; ) {
+
+		map_bh.b_state = 0;
+		map_bh.b_size = 1 << blkbits;
+		if (mpd->get_block(inode, block_in_file, &map_bh, 1))
+			goto confused;
+		if (!buffer_mapped(&map_bh))
+			goto confused;
+		if (buffer_new(&map_bh))
+			clean_bdev_bh_alias(&map_bh);
+		if (buffer_boundary(&map_bh)) {
+			boundary_block = map_bh.b_blocknr;
+			boundary_bdev = map_bh.b_bdev;
+		}
+		if (page_block) {
+			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
+				goto confused;
+		}
+		blocks[page_block++] = map_bh.b_blocknr;
+		boundary = buffer_boundary(&map_bh);
+		bdev = map_bh.b_bdev;
+		if (block_in_file == last_block)
+			break;
+		block_in_file++;
+	}
+	BUG_ON(page_block == 0);
+
+	first_unmapped = page_block;
+
+page_is_mapped:
+	end_index = i_size >> PAGE_SHIFT;
+	if (page->index >= end_index) {
+		/*
+		 * The page straddles i_size.  It must be zeroed out on each
+		 * and every writepage invocation because it may be mmapped.
+		 * "A file is mapped in multiples of the page size.  For a file
+		 * that is not a multiple of the page size, the remaining memory
+		 * is zeroed when mapped, and writes to that region are not
+		 * written out to the file."
+		 */
+		unsigned offset = i_size & (PAGE_SIZE - 1);
+
+		if (page->index > end_index || !offset)
+			goto confused;
+		zero_user_segment(page, offset, PAGE_SIZE);
+	}
+
+	/*
+	 * This page will go to BIO.  Do we need to send this BIO off first?
+	 */
+	if (bio && mpd->last_block_in_bio != blocks[0] - 1)
+		bio = mpage_bio_submit(bio);
+
+alloc_new:
+	if (bio == NULL) {
+		if (first_unmapped == blocks_per_page) {
+			if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
+								page, wbc))
+				goto out;
+		}
+		bio = bio_alloc(bdev, BIO_MAX_VECS,
+				REQ_OP_WRITE | wbc_to_write_flags(wbc),
+				GFP_NOFS);
+		bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+		wbc_init_bio(wbc, bio);
+	}
+
+	/*
+	 * Must try to add the page before marking the buffer clean or
+	 * the confused fail path above (OOM) will be very confused when
+	 * it finds all bh marked clean (i.e. it will not write anything)
+	 */
+	wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
+	length = first_unmapped << blkbits;
+	if (bio_add_page(bio, page, length, 0) < length) {
+		bio = mpage_bio_submit(bio);
+		goto alloc_new;
+	}
+
+	clean_buffers(page, first_unmapped);
+
+	BUG_ON(PageWriteback(page));
+	set_page_writeback(page);
+	unlock_page(page);
+	if (boundary || (first_unmapped != blocks_per_page)) {
+		bio = mpage_bio_submit(bio);
+		if (boundary_block) {
+			write_boundary_block(boundary_bdev,
+					boundary_block, 1 << blkbits);
+		}
+	} else {
+		mpd->last_block_in_bio = blocks[blocks_per_page - 1];
+	}
+	goto out;
+
+confused:
+	if (bio)
+		bio = mpage_bio_submit(bio);
+
+	/*
+	 * The caller has a ref on the inode, so *mapping is stable
+	 */
+	ret = block_write_full_page(page, mpd->get_block, wbc);
+	mapping_set_error(mapping, ret);
+out:
+	mpd->bio = bio;
+	return ret;
+}
+
+/**
+ * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
+ * @mapping: address space structure to write
+ * @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ * @get_block: the filesystem's block mapper function.
+ *
+ * This is a library function, which implements the writepages()
+ * address_space_operation.
+ *
+ * If a page is already under I/O, generic_writepages() skips it, even
+ * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
+ * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
+ * and msync() need to guarantee that all the data which was dirty at the time
+ * the call was made get new I/O started against them.  If wbc->sync_mode is
+ * WB_SYNC_ALL then we were called for data integrity and we must wait for
+ * existing IO to complete.
+ */
+int
+mpage_writepages(struct address_space *mapping,
+		struct writeback_control *wbc, get_block_t get_block)
+{
+	struct mpage_data mpd = {
+		.get_block	= get_block,
+	};
+	struct blk_plug plug;
+	int ret;
+
+	blk_start_plug(&plug);
+	ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
+	if (mpd.bio)
+		mpage_bio_submit(mpd.bio);
+	blk_finish_plug(&plug);
+	return ret;
+}
+EXPORT_SYMBOL(mpage_writepages);