/*
 * 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"

#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_rw_header *nfs_readhdr_alloc(void)
{
	return kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);
}

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

static
int nfs_return_empty_page(struct page *page)
{
	zero_user(page, 0, PAGE_CACHE_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)
{
	pgio->pg_ops = &nfs_pgio_rw_ops;
	pgio->pg_bsize = NFS_SERVER(pgio->pg_inode)->rsize;
}
EXPORT_SYMBOL_GPL(nfs_pageio_reset_read_mds);

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;

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

	nfs_pageio_init_read(&pgio, inode, false,
			     &nfs_async_read_completion_ops);
	nfs_pageio_add_request(&pgio, new);
	nfs_pageio_complete(&pgio);
	NFS_I(inode)->read_io += pgio.pg_bytes_written;
	return 0;
}

static void nfs_readpage_release(struct nfs_page *req)
{
	struct inode *d_inode = req->wb_context->dentry->d_inode;

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

	if (nfs_page_group_sync_on_bit(req, PG_UNLOCKPAGE)) {
		if (PageUptodate(req->wb_page))
			nfs_readpage_to_fscache(d_inode, req->wb_page, 0);

		unlock_page(req->wb_page);
	}

	dprintk("NFS: read done (%s/%Lu %d@%Ld)\n",
			req->wb_context->dentry->d_inode->i_sb->s_id,
			(unsigned long long)NFS_FILEID(req->wb_context->dentry->d_inode),
			req->wb_bytes,
			(long long)req_offset(req));
	nfs_release_request(req);
}

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;

	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);
			}
		}
		bytes += req->wb_bytes;
		if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
			if (bytes <= hdr->good_bytes)
				nfs_page_group_set_uptodate(req);
		} else
			nfs_page_group_set_uptodate(req);
		nfs_list_remove_request(req);
		nfs_readpage_release(req);
	}
out:
	hdr->release(hdr);
}

static void nfs_initiate_read(struct nfs_pgio_data *data, struct rpc_message *msg,
			      struct rpc_task_setup *task_setup_data, int how)
{
	struct inode *inode = data->header->inode;
	int swap_flags = IS_SWAPFILE(inode) ? NFS_RPC_SWAPFLAGS : 0;

	task_setup_data->flags |= swap_flags;
	NFS_PROTO(inode)->read_setup(data, msg);
}

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

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

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_data *data,
			     struct inode *inode)
{
	int status = NFS_PROTO(inode)->read_done(task, data);
	if (status != 0)
		return status;

	nfs_add_stats(inode, NFSIOS_SERVERREADBYTES, data->res.count);

	if (task->tk_status == -ESTALE) {
		set_bit(NFS_INO_STALE, &NFS_I(inode)->flags);
		nfs_mark_for_revalidate(inode);
	}
	return 0;
}

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

	/* This is a short read! */
	nfs_inc_stats(data->header->inode, NFSIOS_SHORTREAD);
	/* Has the server at least made some progress? */
	if (resp->count == 0) {
		nfs_set_pgio_error(data->header, -EIO, argp->offset);
		return;
	}
	/* Yes, so retry the read at the end of the data */
	data->mds_offset += resp->count;
	argp->offset += resp->count;
	argp->pgbase += resp->count;
	argp->count -= resp->count;
	rpc_restart_call_prepare(task);
}

static void nfs_readpage_result(struct rpc_task *task, struct nfs_pgio_data *data)
{
	struct nfs_pgio_header *hdr = data->header;

	if (data->res.eof) {
		loff_t bound;

		bound = data->args.offset + data->res.count;
		spin_lock(&hdr->lock);
		if (bound < hdr->io_start + hdr->good_bytes) {
			set_bit(NFS_IOHDR_EOF, &hdr->flags);
			clear_bit(NFS_IOHDR_ERROR, &hdr->flags);
			hdr->good_bytes = bound - hdr->io_start;
		}
		spin_unlock(&hdr->lock);
	} else if (data->res.count != data->args.count)
		nfs_readpage_retry(task, data);
}

/*
 * 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_CACHE_SIZE, page_file_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;
	}

	error = nfs_readpage_async(ctx, inode, page);

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, NULL, 0, len);
	if (IS_ERR(new))
		goto out_error;

	if (len < PAGE_CACHE_SIZE)
		zero_user_segment(page, len, PAGE_CACHE_SIZE);
	if (!nfs_pageio_add_request(desc->pgio, new)) {
		error = desc->pgio->pg_error;
		goto out_unlock;
	}
	return 0;
out_error:
	error = PTR_ERR(new);
out_unlock:
	unlock_page(page);
	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_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);
	NFS_I(inode)->read_io += pgio.pg_bytes_written;
	npages = (pgio.pg_bytes_written + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_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_rw_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_mode		= FMODE_READ,
	.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,
};