fs/nfs/read.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * linux/fs/nfs/read.c
  *
  * Block I/O for NFS
  *
  * Partial copy of Linus' read cache modifications to fs/nfs/file.c
  * modified for async RPC by okir@monad.swb.de
  */

 #include <linux/time.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/fcntl.h>
 #include <linux/stat.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/pagemap.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/nfs_fs.h>
 #include <linux/nfs_page.h>
 #include <linux/module.h>

 #include "nfs4_fs.h"
 #include "internal.h"
 #include "iostat.h"
 #include "fscache.h"
 #include "pnfs.h"
 #include "nfstrace.h"

 #define NFSDBG_FACILITY		NFSDBG_PAGECACHE

 static const struct nfs_pgio_completion_ops nfs_async_read_completion_ops;
 static const struct nfs_rw_ops nfs_rw_read_ops;

 static struct kmem_cache *nfs_rdata_cachep;

 static struct nfs_pgio_header *nfs_readhdr_alloc(void)
 {
 	struct nfs_pgio_header *p = kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);

 	if (p)
 		p->rw_mode = FMODE_READ;
 	return p;
 }

 static void nfs_readhdr_free(struct nfs_pgio_header *rhdr)
 {
 	kmem_cache_free(nfs_rdata_cachep, rhdr);
 }

 static
 int nfs_return_empty_page(struct page *page)
 {
 	zero_user(page, 0, PAGE_SIZE);
 	SetPageUptodate(page);
 	unlock_page(page);
 	return 0;
 }

 void nfs_pageio_init_read(struct nfs_pageio_descriptor *pgio,
 			      struct inode *inode, bool force_mds,
 			      const struct nfs_pgio_completion_ops *compl_ops)
 {
 	struct nfs_server *server = NFS_SERVER(inode);
 	const struct nfs_pageio_ops *pg_ops = &nfs_pgio_rw_ops;

 #ifdef CONFIG_NFS_V4_1
 	if (server->pnfs_curr_ld && !force_mds)
 		pg_ops = server->pnfs_curr_ld->pg_read_ops;
 #endif
 	nfs_pageio_init(pgio, inode, pg_ops, compl_ops, &nfs_rw_read_ops,
 			server->rsize, 0);
 }
 EXPORT_SYMBOL_GPL(nfs_pageio_init_read);

 void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio)
 {
 	struct nfs_pgio_mirror *mirror;

 	if (pgio->pg_ops && pgio->pg_ops->pg_cleanup)
 		pgio->pg_ops->pg_cleanup(pgio);

 	pgio->pg_ops = &nfs_pgio_rw_ops;

 	/* read path should never have more than one mirror */
 	WARN_ON_ONCE(pgio->pg_mirror_count != 1);

 	mirror = &pgio->pg_mirrors[0];
 	mirror->pg_bsize = NFS_SERVER(pgio->pg_inode)->rsize;
 }
 EXPORT_SYMBOL_GPL(nfs_pageio_reset_read_mds);

 static void nfs_readpage_release(struct nfs_page *req, int error)
 {
 	struct inode *inode = d_inode(nfs_req_openctx(req)->dentry);
 	struct page *page = req->wb_page;

 	dprintk("NFS: read done (%s/%llu %d@%lld)\n", inode->i_sb->s_id,
 		(unsigned long long)NFS_FILEID(inode), req->wb_bytes,
 		(long long)req_offset(req));

 	if (nfs_error_is_fatal_on_server(error) && error != -ETIMEDOUT)
 		SetPageError(page);
 	if (nfs_page_group_sync_on_bit(req, PG_UNLOCKPAGE)) {
 		struct address_space *mapping = page_file_mapping(page);

 		if (PageUptodate(page))
 			nfs_readpage_to_fscache(inode, page, 0);
 		else if (!PageError(page) && !PagePrivate(page))
 			generic_error_remove_page(mapping, page);
 		unlock_page(page);
 	}
 	nfs_release_request(req);
 }

 int nfs_readpage_async(struct nfs_open_context *ctx, struct inode *inode,
 		       struct page *page)
 {
 	struct nfs_page	*new;
 	unsigned int len;
 	struct nfs_pageio_descriptor pgio;
 	struct nfs_pgio_mirror *pgm;

 	len = nfs_page_length(page);
 	if (len == 0)
 		return nfs_return_empty_page(page);
 	new = nfs_create_request(ctx, page, 0, len);
 	if (IS_ERR(new)) {
 		unlock_page(page);
 		return PTR_ERR(new);
 	}
 	if (len < PAGE_SIZE)
 		zero_user_segment(page, len, PAGE_SIZE);

 	nfs_pageio_init_read(&pgio, inode, false,
 			     &nfs_async_read_completion_ops);
 	if (!nfs_pageio_add_request(&pgio, new)) {
 		nfs_list_remove_request(new);
 		nfs_readpage_release(new, pgio.pg_error);
 	}
 	nfs_pageio_complete(&pgio);

 	/* It doesn't make sense to do mirrored reads! */
 	WARN_ON_ONCE(pgio.pg_mirror_count != 1);

 	pgm = &pgio.pg_mirrors[0];
 	NFS_I(inode)->read_io += pgm->pg_bytes_written;

 	return pgio.pg_error < 0 ? pgio.pg_error : 0;
 }

 static void nfs_page_group_set_uptodate(struct nfs_page *req)
 {
 	if (nfs_page_group_sync_on_bit(req, PG_UPTODATE))
 		SetPageUptodate(req->wb_page);
 }

 static void nfs_read_completion(struct nfs_pgio_header *hdr)
 {
 	unsigned long bytes = 0;
 	int error;

 	if (test_bit(NFS_IOHDR_REDO, &hdr->flags))
 		goto out;
 	while (!list_empty(&hdr->pages)) {
 		struct nfs_page *req = nfs_list_entry(hdr->pages.next);
 		struct page *page = req->wb_page;
 		unsigned long start = req->wb_pgbase;
 		unsigned long end = req->wb_pgbase + req->wb_bytes;

 		if (test_bit(NFS_IOHDR_EOF, &hdr->flags)) {
 			/* note: regions of the page not covered by a
 			 * request are zeroed in nfs_readpage_async /
 			 * readpage_async_filler */
 			if (bytes > hdr->good_bytes) {
 				/* nothing in this request was good, so zero
 				 * the full extent of the request */
 				zero_user_segment(page, start, end);

 			} else if (hdr->good_bytes - bytes < req->wb_bytes) {
 				/* part of this request has good bytes, but
 				 * not all. zero the bad bytes */
 				start += hdr->good_bytes - bytes;
 				WARN_ON(start < req->wb_pgbase);
 				zero_user_segment(page, start, end);
 			}
 		}
 		error = 0;
 		bytes += req->wb_bytes;
 		if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
 			if (bytes <= hdr->good_bytes)
 				nfs_page_group_set_uptodate(req);
 			else {
 				error = hdr->error;
 				xchg(&nfs_req_openctx(req)->error, error);
 			}
 		} else
 			nfs_page_group_set_uptodate(req);
 		nfs_list_remove_request(req);
 		nfs_readpage_release(req, error);
 	}
 out:
 	hdr->release(hdr);
 }

 static void nfs_initiate_read(struct nfs_pgio_header *hdr,
 			      struct rpc_message *msg,
 			      const struct nfs_rpc_ops *rpc_ops,
 			      struct rpc_task_setup *task_setup_data, int how)
 {
 	struct inode *inode = hdr->inode;
 	int swap_flags = IS_SWAPFILE(inode) ? NFS_RPC_SWAPFLAGS : 0;

 	task_setup_data->flags |= swap_flags;
 	rpc_ops->read_setup(hdr, msg);
 	trace_nfs_initiate_read(hdr);
 }

 static void
 nfs_async_read_error(struct list_head *head, int error)
 {
 	struct nfs_page	*req;

 	while (!list_empty(head)) {
 		req = nfs_list_entry(head->next);
 		nfs_list_remove_request(req);
 		nfs_readpage_release(req, error);
 	}
 }

 static const struct nfs_pgio_completion_ops nfs_async_read_completion_ops = {
 	.error_cleanup = nfs_async_read_error,
 	.completion = nfs_read_completion,
 };

 /*
  * This is the callback from RPC telling us whether a reply was
  * received or some error occurred (timeout or socket shutdown).
  */
 static int nfs_readpage_done(struct rpc_task *task,
 			     struct nfs_pgio_header *hdr,
 			     struct inode *inode)
 {
 	int status = NFS_PROTO(inode)->read_done(task, hdr);
 	if (status != 0)
 		return status;

 	nfs_add_stats(inode, NFSIOS_SERVERREADBYTES, hdr->res.count);
 	trace_nfs_readpage_done(task, hdr);

 	if (task->tk_status == -ESTALE) {
 		nfs_set_inode_stale(inode);
 		nfs_mark_for_revalidate(inode);
 	}
 	return 0;
 }

 static void nfs_readpage_retry(struct rpc_task *task,
 			       struct nfs_pgio_header *hdr)
 {
 	struct nfs_pgio_args *argp = &hdr->args;
 	struct nfs_pgio_res  *resp = &hdr->res;

 	/* This is a short read! */
 	nfs_inc_stats(hdr->inode, NFSIOS_SHORTREAD);
 	/* Has the server at least made some progress? */
 	if (resp->count == 0) {
 		nfs_set_pgio_error(hdr, -EIO, argp->offset);
 		return;
 	}

 	/* For non rpc-based layout drivers, retry-through-MDS */
 	if (!task->tk_ops) {
 		hdr->pnfs_error = -EAGAIN;
 		return;
 	}

 	/* Yes, so retry the read at the end of the hdr */
 	hdr->mds_offset += resp->count;
 	argp->offset += resp->count;
 	argp->pgbase += resp->count;
 	argp->count -= resp->count;
 	resp->count = 0;
 	resp->eof = 0;
 	rpc_restart_call_prepare(task);
 }

 static void nfs_readpage_result(struct rpc_task *task,
 				struct nfs_pgio_header *hdr)
 {
 	if (hdr->res.eof) {
 		loff_t pos = hdr->args.offset + hdr->res.count;
 		unsigned int new = pos - hdr->io_start;

 		if (hdr->good_bytes > new) {
 			hdr->good_bytes = new;
 			set_bit(NFS_IOHDR_EOF, &hdr->flags);
 			clear_bit(NFS_IOHDR_ERROR, &hdr->flags);
 		}
 	} else if (hdr->res.count < hdr->args.count)
 		nfs_readpage_retry(task, hdr);
 }

 /*
  * Read a page over NFS.
  * We read the page synchronously in the following case:
  *  -	The error flag is set for this page. This happens only when a
  *	previous async read operation failed.
  */
 int nfs_readpage(struct file *file, struct page *page)
 {
 	struct nfs_open_context *ctx;
 	struct inode *inode = page_file_mapping(page)->host;
 	int		error;

 	dprintk("NFS: nfs_readpage (%p %ld@%lu)\n",
 		page, PAGE_SIZE, page_index(page));
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGE);
 	nfs_add_stats(inode, NFSIOS_READPAGES, 1);

 	/*
 	 * Try to flush any pending writes to the file..
 	 *
 	 * NOTE! Because we own the page lock, there cannot
 	 * be any new pending writes generated at this point
 	 * for this page (other pages can be written to).
 	 */
 	error = nfs_wb_page(inode, page);
 	if (error)
 		goto out_unlock;
 	if (PageUptodate(page))
 		goto out_unlock;

 	error = -ESTALE;
 	if (NFS_STALE(inode))
 		goto out_unlock;

 	if (file == NULL) {
 		error = -EBADF;
 		ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
 		if (ctx == NULL)
 			goto out_unlock;
 	} else
 		ctx = get_nfs_open_context(nfs_file_open_context(file));

 	if (!IS_SYNC(inode)) {
 		error = nfs_readpage_from_fscache(ctx, inode, page);
 		if (error == 0)
 			goto out;
 	}

 	xchg(&ctx->error, 0);
 	error = nfs_readpage_async(ctx, inode, page);
 	if (!error) {
 		error = wait_on_page_locked_killable(page);
 		if (!PageUptodate(page) && !error)
 			error = xchg(&ctx->error, 0);
 	}
 out:
 	put_nfs_open_context(ctx);
 	return error;
 out_unlock:
 	unlock_page(page);
 	return error;
 }

 struct nfs_readdesc {
 	struct nfs_pageio_descriptor *pgio;
 	struct nfs_open_context *ctx;
 };

 static int
 readpage_async_filler(void *data, struct page *page)
 {
 	struct nfs_readdesc *desc = (struct nfs_readdesc *)data;
 	struct nfs_page *new;
 	unsigned int len;
 	int error;

 	len = nfs_page_length(page);
 	if (len == 0)
 		return nfs_return_empty_page(page);

 	new = nfs_create_request(desc->ctx, page, 0, len);
 	if (IS_ERR(new))
 		goto out_error;

 	if (len < PAGE_SIZE)
 		zero_user_segment(page, len, PAGE_SIZE);
 	if (!nfs_pageio_add_request(desc->pgio, new)) {
 		nfs_list_remove_request(new);
 		error = desc->pgio->pg_error;
 		nfs_readpage_release(new, error);
 		goto out;
 	}
 	return 0;
 out_error:
 	error = PTR_ERR(new);
 	unlock_page(page);
 out:
 	return error;
 }

 int nfs_readpages(struct file *filp, struct address_space *mapping,
 		struct list_head *pages, unsigned nr_pages)
 {
 	struct nfs_pageio_descriptor pgio;
 	struct nfs_pgio_mirror *pgm;
 	struct nfs_readdesc desc = {
 		.pgio = &pgio,
 	};
 	struct inode *inode = mapping->host;
 	unsigned long npages;
 	int ret = -ESTALE;

 	dprintk("NFS: nfs_readpages (%s/%Lu %d)\n",
 			inode->i_sb->s_id,
 			(unsigned long long)NFS_FILEID(inode),
 			nr_pages);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);

 	if (NFS_STALE(inode))
 		goto out;

 	if (filp == NULL) {
 		desc.ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
 		if (desc.ctx == NULL)
 			return -EBADF;
 	} else
 		desc.ctx = get_nfs_open_context(nfs_file_open_context(filp));

 	/* attempt to read as many of the pages as possible from the cache
 	 * - this returns -ENOBUFS immediately if the cookie is negative
 	 */
 	ret = nfs_readpages_from_fscache(desc.ctx, inode, mapping,
 					 pages, &nr_pages);
 	if (ret == 0)
 		goto read_complete; /* all pages were read */

 	nfs_pageio_init_read(&pgio, inode, false,
 			     &nfs_async_read_completion_ops);

 	ret = read_cache_pages(mapping, pages, readpage_async_filler, &desc);
 	nfs_pageio_complete(&pgio);

 	/* It doesn't make sense to do mirrored reads! */
 	WARN_ON_ONCE(pgio.pg_mirror_count != 1);

 	pgm = &pgio.pg_mirrors[0];
 	NFS_I(inode)->read_io += pgm->pg_bytes_written;
 	npages = (pgm->pg_bytes_written + PAGE_SIZE - 1) >>
 		 PAGE_SHIFT;
 	nfs_add_stats(inode, NFSIOS_READPAGES, npages);
 read_complete:
 	put_nfs_open_context(desc.ctx);
 out:
 	return ret;
 }

 int __init nfs_init_readpagecache(void)
 {
 	nfs_rdata_cachep = kmem_cache_create("nfs_read_data",
 					     sizeof(struct nfs_pgio_header),
 					     0, SLAB_HWCACHE_ALIGN,
 					     NULL);
 	if (nfs_rdata_cachep == NULL)
 		return -ENOMEM;

 	return 0;
 }

 void nfs_destroy_readpagecache(void)
 {
 	kmem_cache_destroy(nfs_rdata_cachep);
 }

 static const struct nfs_rw_ops nfs_rw_read_ops = {
 	.rw_alloc_header	= nfs_readhdr_alloc,
 	.rw_free_header		= nfs_readhdr_free,
 	.rw_done		= nfs_readpage_done,
 	.rw_result		= nfs_readpage_result,
 	.rw_initiate		= nfs_initiate_read,
 };
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* linux/fs/nfs/read.c
	*
	* Block I/O for NFS
	*
	* Partial copy of Linus' read cache modifications to fs/nfs/file.c
	* modified for async RPC by okir@monad.swb.de
	*/

	#include <linux/time.h>
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/fcntl.h>
	#include <linux/stat.h>
	#include <linux/mm.h>
	#include <linux/slab.h>
	#include <linux/pagemap.h>
	#include <linux/sunrpc/clnt.h>
	#include <linux/nfs_fs.h>
	#include <linux/nfs_page.h>
	#include <linux/module.h>

	#include "nfs4_fs.h"
	#include "internal.h"
	#include "iostat.h"
	#include "fscache.h"
	#include "pnfs.h"
	#include "nfstrace.h"

	#define NFSDBG_FACILITY NFSDBG_PAGECACHE

	static const struct nfs_pgio_completion_ops nfs_async_read_completion_ops;
	static const struct nfs_rw_ops nfs_rw_read_ops;

	static struct kmem_cache *nfs_rdata_cachep;

	static struct nfs_pgio_header *nfs_readhdr_alloc(void)
	{
	struct nfs_pgio_header *p = kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);

	if (p)
	p->rw_mode = FMODE_READ;
	return p;
	}

	static void nfs_readhdr_free(struct nfs_pgio_header *rhdr)
	{
	kmem_cache_free(nfs_rdata_cachep, rhdr);
	}

	static
	int nfs_return_empty_page(struct page *page)
	{
	zero_user(page, 0, PAGE_SIZE);
	SetPageUptodate(page);
	unlock_page(page);
	return 0;
	}

	void nfs_pageio_init_read(struct nfs_pageio_descriptor *pgio,
	struct inode *inode, bool force_mds,
	const struct nfs_pgio_completion_ops *compl_ops)
	{
	struct nfs_server *server = NFS_SERVER(inode);
	const struct nfs_pageio_ops *pg_ops = &nfs_pgio_rw_ops;

	#ifdef CONFIG_NFS_V4_1
	if (server->pnfs_curr_ld && !force_mds)
	pg_ops = server->pnfs_curr_ld->pg_read_ops;
	#endif
	nfs_pageio_init(pgio, inode, pg_ops, compl_ops, &nfs_rw_read_ops,
	server->rsize, 0);
	}
	EXPORT_SYMBOL_GPL(nfs_pageio_init_read);

	void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio)
	{
	struct nfs_pgio_mirror *mirror;

	if (pgio->pg_ops && pgio->pg_ops->pg_cleanup)
	pgio->pg_ops->pg_cleanup(pgio);

	pgio->pg_ops = &nfs_pgio_rw_ops;

	/* read path should never have more than one mirror */
	WARN_ON_ONCE(pgio->pg_mirror_count != 1);

	mirror = &pgio->pg_mirrors[0];
	mirror->pg_bsize = NFS_SERVER(pgio->pg_inode)->rsize;
	}
	EXPORT_SYMBOL_GPL(nfs_pageio_reset_read_mds);

	static void nfs_readpage_release(struct nfs_page *req, int error)
	{
	struct inode *inode = d_inode(nfs_req_openctx(req)->dentry);
	struct page *page = req->wb_page;

	dprintk("NFS: read done (%s/%llu %d@%lld)\n", inode->i_sb->s_id,
	(unsigned long long)NFS_FILEID(inode), req->wb_bytes,
	(long long)req_offset(req));

	if (nfs_error_is_fatal_on_server(error) && error != -ETIMEDOUT)
	SetPageError(page);
	if (nfs_page_group_sync_on_bit(req, PG_UNLOCKPAGE)) {
	struct address_space *mapping = page_file_mapping(page);

	if (PageUptodate(page))
	nfs_readpage_to_fscache(inode, page, 0);
	else if (!PageError(page) && !PagePrivate(page))
	generic_error_remove_page(mapping, page);
	unlock_page(page);
	}
	nfs_release_request(req);
	}

	int nfs_readpage_async(struct nfs_open_context ctx, struct inode inode,
	struct page *page)
	{
	struct nfs_page *new;
	unsigned int len;
	struct nfs_pageio_descriptor pgio;
	struct nfs_pgio_mirror *pgm;

	len = nfs_page_length(page);
	if (len == 0)
	return nfs_return_empty_page(page);
	new = nfs_create_request(ctx, page, 0, len);
	if (IS_ERR(new)) {
	unlock_page(page);
	return PTR_ERR(new);
	}
	if (len < PAGE_SIZE)
	zero_user_segment(page, len, PAGE_SIZE);

	nfs_pageio_init_read(&pgio, inode, false,
	&nfs_async_read_completion_ops);
	if (!nfs_pageio_add_request(&pgio, new)) {
	nfs_list_remove_request(new);
	nfs_readpage_release(new, pgio.pg_error);
	}
	nfs_pageio_complete(&pgio);

	/* It doesn't make sense to do mirrored reads! */
	WARN_ON_ONCE(pgio.pg_mirror_count != 1);

	pgm = &pgio.pg_mirrors[0];
	NFS_I(inode)->read_io += pgm->pg_bytes_written;

	return pgio.pg_error < 0 ? pgio.pg_error : 0;
	}

	static void nfs_page_group_set_uptodate(struct nfs_page *req)
	{
	if (nfs_page_group_sync_on_bit(req, PG_UPTODATE))
	SetPageUptodate(req->wb_page);
	}

	static void nfs_read_completion(struct nfs_pgio_header *hdr)
	{
	unsigned long bytes = 0;
	int error;

	if (test_bit(NFS_IOHDR_REDO, &hdr->flags))
	goto out;
	while (!list_empty(&hdr->pages)) {
	struct nfs_page *req = nfs_list_entry(hdr->pages.next);
	struct page *page = req->wb_page;
	unsigned long start = req->wb_pgbase;
	unsigned long end = req->wb_pgbase + req->wb_bytes;

	if (test_bit(NFS_IOHDR_EOF, &hdr->flags)) {
	/* note: regions of the page not covered by a
	* request are zeroed in nfs_readpage_async /
	* readpage_async_filler */
	if (bytes > hdr->good_bytes) {
	/* nothing in this request was good, so zero
	* the full extent of the request */
	zero_user_segment(page, start, end);

	} else if (hdr->good_bytes - bytes < req->wb_bytes) {
	/* part of this request has good bytes, but
	* not all. zero the bad bytes */
	start += hdr->good_bytes - bytes;
	WARN_ON(start < req->wb_pgbase);
	zero_user_segment(page, start, end);
	}
	}
	error = 0;
	bytes += req->wb_bytes;
	if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
	if (bytes <= hdr->good_bytes)
	nfs_page_group_set_uptodate(req);
	else {
	error = hdr->error;
	xchg(&nfs_req_openctx(req)->error, error);
	}
	} else
	nfs_page_group_set_uptodate(req);
	nfs_list_remove_request(req);
	nfs_readpage_release(req, error);
	}
	out:
	hdr->release(hdr);
	}

	static void nfs_initiate_read(struct nfs_pgio_header *hdr,
	struct rpc_message *msg,
	const struct nfs_rpc_ops *rpc_ops,
	struct rpc_task_setup *task_setup_data, int how)
	{
	struct inode *inode = hdr->inode;
	int swap_flags = IS_SWAPFILE(inode) ? NFS_RPC_SWAPFLAGS : 0;

	task_setup_data->flags \|= swap_flags;
	rpc_ops->read_setup(hdr, msg);
	trace_nfs_initiate_read(hdr);
	}

	static void
	nfs_async_read_error(struct list_head *head, int error)
	{
	struct nfs_page *req;

	while (!list_empty(head)) {
	req = nfs_list_entry(head->next);
	nfs_list_remove_request(req);
	nfs_readpage_release(req, error);
	}
	}

	static const struct nfs_pgio_completion_ops nfs_async_read_completion_ops = {
	.error_cleanup = nfs_async_read_error,
	.completion = nfs_read_completion,
	};

	/*
	* This is the callback from RPC telling us whether a reply was
	* received or some error occurred (timeout or socket shutdown).
	*/
	static int nfs_readpage_done(struct rpc_task *task,
	struct nfs_pgio_header *hdr,
	struct inode *inode)
	{
	int status = NFS_PROTO(inode)->read_done(task, hdr);
	if (status != 0)
	return status;

	nfs_add_stats(inode, NFSIOS_SERVERREADBYTES, hdr->res.count);
	trace_nfs_readpage_done(task, hdr);

	if (task->tk_status == -ESTALE) {
	nfs_set_inode_stale(inode);
	nfs_mark_for_revalidate(inode);
	}
	return 0;
	}

	static void nfs_readpage_retry(struct rpc_task *task,
	struct nfs_pgio_header *hdr)
	{
	struct nfs_pgio_args *argp = &hdr->args;
	struct nfs_pgio_res *resp = &hdr->res;

	/* This is a short read! */
	nfs_inc_stats(hdr->inode, NFSIOS_SHORTREAD);
	/* Has the server at least made some progress? */
	if (resp->count == 0) {
	nfs_set_pgio_error(hdr, -EIO, argp->offset);
	return;
	}

	/* For non rpc-based layout drivers, retry-through-MDS */
	if (!task->tk_ops) {
	hdr->pnfs_error = -EAGAIN;
	return;
	}

	/* Yes, so retry the read at the end of the hdr */
	hdr->mds_offset += resp->count;
	argp->offset += resp->count;
	argp->pgbase += resp->count;
	argp->count -= resp->count;
	resp->count = 0;
	resp->eof = 0;
	rpc_restart_call_prepare(task);
	}

	static void nfs_readpage_result(struct rpc_task *task,
	struct nfs_pgio_header *hdr)
	{
	if (hdr->res.eof) {
	loff_t pos = hdr->args.offset + hdr->res.count;
	unsigned int new = pos - hdr->io_start;

	if (hdr->good_bytes > new) {
	hdr->good_bytes = new;
	set_bit(NFS_IOHDR_EOF, &hdr->flags);
	clear_bit(NFS_IOHDR_ERROR, &hdr->flags);
	}
	} else if (hdr->res.count < hdr->args.count)
	nfs_readpage_retry(task, hdr);
	}

	/*
	* Read a page over NFS.
	* We read the page synchronously in the following case:
	* - The error flag is set for this page. This happens only when a
	* previous async read operation failed.
	*/
	int nfs_readpage(struct file file, struct page page)
	{
	struct nfs_open_context *ctx;
	struct inode *inode = page_file_mapping(page)->host;
	int error;

	dprintk("NFS: nfs_readpage (%p %ld@%lu)\n",
	page, PAGE_SIZE, page_index(page));
	nfs_inc_stats(inode, NFSIOS_VFSREADPAGE);
	nfs_add_stats(inode, NFSIOS_READPAGES, 1);

	/*
	* Try to flush any pending writes to the file..
	*
	* NOTE! Because we own the page lock, there cannot
	* be any new pending writes generated at this point
	* for this page (other pages can be written to).
	*/
	error = nfs_wb_page(inode, page);
	if (error)
	goto out_unlock;
	if (PageUptodate(page))
	goto out_unlock;

	error = -ESTALE;
	if (NFS_STALE(inode))
	goto out_unlock;

	if (file == NULL) {
	error = -EBADF;
	ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
	if (ctx == NULL)
	goto out_unlock;
	} else
	ctx = get_nfs_open_context(nfs_file_open_context(file));

	if (!IS_SYNC(inode)) {
	error = nfs_readpage_from_fscache(ctx, inode, page);
	if (error == 0)
	goto out;
	}

	xchg(&ctx->error, 0);
	error = nfs_readpage_async(ctx, inode, page);
	if (!error) {
	error = wait_on_page_locked_killable(page);
	if (!PageUptodate(page) && !error)
	error = xchg(&ctx->error, 0);
	}
	out:
	put_nfs_open_context(ctx);
	return error;
	out_unlock:
	unlock_page(page);
	return error;
	}

	struct nfs_readdesc {
	struct nfs_pageio_descriptor *pgio;
	struct nfs_open_context *ctx;
	};

	static int
	readpage_async_filler(void data, struct page page)
	{
	struct nfs_readdesc desc = (struct nfs_readdesc )data;
	struct nfs_page *new;
	unsigned int len;
	int error;

	len = nfs_page_length(page);
	if (len == 0)
	return nfs_return_empty_page(page);

	new = nfs_create_request(desc->ctx, page, 0, len);
	if (IS_ERR(new))
	goto out_error;

	if (len < PAGE_SIZE)
	zero_user_segment(page, len, PAGE_SIZE);
	if (!nfs_pageio_add_request(desc->pgio, new)) {
	nfs_list_remove_request(new);
	error = desc->pgio->pg_error;
	nfs_readpage_release(new, error);
	goto out;
	}
	return 0;
	out_error:
	error = PTR_ERR(new);
	unlock_page(page);
	out:
	return error;
	}

	int nfs_readpages(struct file filp, struct address_space mapping,
	struct list_head *pages, unsigned nr_pages)
	{
	struct nfs_pageio_descriptor pgio;
	struct nfs_pgio_mirror *pgm;
	struct nfs_readdesc desc = {
	.pgio = &pgio,
	};
	struct inode *inode = mapping->host;
	unsigned long npages;
	int ret = -ESTALE;

	dprintk("NFS: nfs_readpages (%s/%Lu %d)\n",
	inode->i_sb->s_id,
	(unsigned long long)NFS_FILEID(inode),
	nr_pages);
	nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);

	if (NFS_STALE(inode))
	goto out;

	if (filp == NULL) {
	desc.ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
	if (desc.ctx == NULL)
	return -EBADF;
	} else
	desc.ctx = get_nfs_open_context(nfs_file_open_context(filp));

	/* attempt to read as many of the pages as possible from the cache
	* - this returns -ENOBUFS immediately if the cookie is negative
	*/
	ret = nfs_readpages_from_fscache(desc.ctx, inode, mapping,
	pages, &nr_pages);
	if (ret == 0)
	goto read_complete; /* all pages were read */

	nfs_pageio_init_read(&pgio, inode, false,
	&nfs_async_read_completion_ops);

	ret = read_cache_pages(mapping, pages, readpage_async_filler, &desc);
	nfs_pageio_complete(&pgio);

	/* It doesn't make sense to do mirrored reads! */
	WARN_ON_ONCE(pgio.pg_mirror_count != 1);

	pgm = &pgio.pg_mirrors[0];
	NFS_I(inode)->read_io += pgm->pg_bytes_written;
	npages = (pgm->pg_bytes_written + PAGE_SIZE - 1) >>
	PAGE_SHIFT;
	nfs_add_stats(inode, NFSIOS_READPAGES, npages);
	read_complete:
	put_nfs_open_context(desc.ctx);
	out:
	return ret;
	}

	int __init nfs_init_readpagecache(void)
	{
	nfs_rdata_cachep = kmem_cache_create("nfs_read_data",
	sizeof(struct nfs_pgio_header),
	0, SLAB_HWCACHE_ALIGN,
	NULL);
	if (nfs_rdata_cachep == NULL)
	return -ENOMEM;

	return 0;
	}

	void nfs_destroy_readpagecache(void)
	{
	kmem_cache_destroy(nfs_rdata_cachep);
	}

	static const struct nfs_rw_ops nfs_rw_read_ops = {
	.rw_alloc_header = nfs_readhdr_alloc,
	.rw_free_header = nfs_readhdr_free,
	.rw_done = nfs_readpage_done,
	.rw_result = nfs_readpage_result,
	.rw_initiate = nfs_initiate_read,
	};