/*
 * 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"

#define NFSDBG_FACILITY         NFSDBG_PAGECACHE

static const struct nfs_pageio_ops nfs_pageio_read_ops;
static const struct rpc_call_ops nfs_read_common_ops;
static const struct nfs_pgio_completion_ops nfs_async_read_completion_ops;

static struct kmem_cache *nfs_rdata_cachep;

struct nfs_read_header *nfs_readhdr_alloc(void)
{
        struct nfs_read_header *rhdr;

        rhdr = kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);
        if (rhdr) {
                struct nfs_pgio_header *hdr = &rhdr->header;

                INIT_LIST_HEAD(&hdr->pages);
                INIT_LIST_HEAD(&hdr->rpc_list);
                spin_lock_init(&hdr->lock);
                atomic_set(&hdr->refcnt, 0);
        }
        return rhdr;
}
EXPORT_SYMBOL_GPL(nfs_readhdr_alloc);

static struct nfs_read_data *nfs_readdata_alloc(struct nfs_pgio_header *hdr,
                                                unsigned int pagecount)
{
        struct nfs_read_data *data, *prealloc;

        prealloc = &container_of(hdr, struct nfs_read_header, header)->rpc_data;
        if (prealloc->header == NULL)
                data = prealloc;
        else
                data = kzalloc(sizeof(*data), GFP_KERNEL);
        if (!data)
                goto out;

        if (nfs_pgarray_set(&data->pages, pagecount)) {
                data->header = hdr;
                atomic_inc(&hdr->refcnt);
        } else {
                if (data != prealloc)
                        kfree(data);
                data = NULL;
        }
out:
        return data;
}

void nfs_readhdr_free(struct nfs_pgio_header *hdr)
{
        struct nfs_read_header *rhdr = container_of(hdr, struct nfs_read_header, header);

        kmem_cache_free(nfs_rdata_cachep, rhdr);
}
EXPORT_SYMBOL_GPL(nfs_readhdr_free);

void nfs_readdata_release(struct nfs_read_data *rdata)
{
        struct nfs_pgio_header *hdr = rdata->header;
        struct nfs_read_header *read_header = container_of(hdr, struct nfs_read_header, header);

        put_nfs_open_context(rdata->args.context);
        if (rdata->pages.pagevec != rdata->pages.page_array)
                kfree(rdata->pages.pagevec);
        if (rdata == &read_header->rpc_data) {
                rdata->header = NULL;
                rdata = NULL;
        }
        if (atomic_dec_and_test(&hdr->refcnt))
                hdr->completion_ops->completion(hdr);
        /* Note: we only free the rpc_task after callbacks are done.
         * See the comment in rpc_free_task() for why
         */
        kfree(rdata);
}
EXPORT_SYMBOL_GPL(nfs_readdata_release);

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,
                              const struct nfs_pgio_completion_ops *compl_ops)
{
        nfs_pageio_init(pgio, inode, &nfs_pageio_read_ops, compl_ops,
                        NFS_SERVER(inode)->rsize, 0);
}
EXPORT_SYMBOL_GPL(nfs_pageio_init_read);

void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio)
{
        pgio->pg_ops = &nfs_pageio_read_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, inode, page, 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_PROTO(inode)->read_pageio_init(&pgio, inode, &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;

        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/%Ld %d@%Ld)\n",
                        req->wb_context->dentry->d_inode->i_sb->s_id,
                        (long long)NFS_FILEID(req->wb_context->dentry->d_inode),
                        req->wb_bytes,
                        (long long)req_offset(req));
        nfs_release_request(req);
}

/* Note io was page aligned */
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;

                if (test_bit(NFS_IOHDR_EOF, &hdr->flags)) {
                        if (bytes > hdr->good_bytes)
                                zero_user(page, 0, PAGE_SIZE);
                        else if (hdr->good_bytes - bytes < PAGE_SIZE)
                                zero_user_segment(page,
                                        hdr->good_bytes & ~PAGE_MASK,
                                        PAGE_SIZE);
                }
                bytes += req->wb_bytes;
                if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
                        if (bytes <= hdr->good_bytes)
                                SetPageUptodate(page);
                } else
                        SetPageUptodate(page);
                nfs_list_remove_request(req);
                nfs_readpage_release(req);
        }
out:
        hdr->release(hdr);
}

int nfs_initiate_read(struct rpc_clnt *clnt,
                      struct nfs_read_data *data,
                      const struct rpc_call_ops *call_ops, int flags)
{
        struct inode *inode = data->header->inode;
        int swap_flags = IS_SWAPFILE(inode) ? NFS_RPC_SWAPFLAGS : 0;
        struct rpc_task *task;
        struct rpc_message msg = {
                .rpc_argp = &data->args,
                .rpc_resp = &data->res,
                .rpc_cred = data->header->cred,
        };
        struct rpc_task_setup task_setup_data = {
                .task = &data->task,
                .rpc_client = clnt,
                .rpc_message = &msg,
                .callback_ops = call_ops,
                .callback_data = data,
                .workqueue = nfsiod_workqueue,
                .flags = RPC_TASK_ASYNC | swap_flags | flags,
        };

        /* Set up the initial task struct. */
        NFS_PROTO(inode)->read_setup(data, &msg);

        dprintk("NFS: %5u initiated read call (req %s/%lld, %u bytes @ "
                        "offset %llu)\n",
                        data->task.tk_pid,
                        inode->i_sb->s_id,
                        (long long)NFS_FILEID(inode),
                        data->args.count,
                        (unsigned long long)data->args.offset);

        task = rpc_run_task(&task_setup_data);
        if (IS_ERR(task))
                return PTR_ERR(task);
        rpc_put_task(task);
        return 0;
}
EXPORT_SYMBOL_GPL(nfs_initiate_read);

/*
 * Set up the NFS read request struct
 */
static void nfs_read_rpcsetup(struct nfs_read_data *data,
                unsigned int count, unsigned int offset)
{
        struct nfs_page *req = data->header->req;

        data->args.fh     = NFS_FH(data->header->inode);
        data->args.offset = req_offset(req) + offset;
        data->args.pgbase = req->wb_pgbase + offset;
        data->args.pages  = data->pages.pagevec;
        data->args.count  = count;
        data->args.context = get_nfs_open_context(req->wb_context);
        data->args.lock_context = req->wb_lock_context;

        data->res.fattr   = &data->fattr;
        data->res.count   = count;
        data->res.eof     = 0;
        nfs_fattr_init(&data->fattr);
}

static int nfs_do_read(struct nfs_read_data *data,
                const struct rpc_call_ops *call_ops)
{
        struct inode *inode = data->header->inode;

        return nfs_initiate_read(NFS_CLIENT(inode), data, call_ops, 0);
}

static int
nfs_do_multiple_reads(struct list_head *head,
                const struct rpc_call_ops *call_ops)
{
        struct nfs_read_data *data;
        int ret = 0;

        while (!list_empty(head)) {
                int ret2;

                data = list_first_entry(head, struct nfs_read_data, list);
                list_del_init(&data->list);

                ret2 = nfs_do_read(data, call_ops);
                if (ret == 0)
                        ret = ret2;
        }
        return ret;
}

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,
};

static void nfs_pagein_error(struct nfs_pageio_descriptor *desc,
                struct nfs_pgio_header *hdr)
{
        set_bit(NFS_IOHDR_REDO, &hdr->flags);
        while (!list_empty(&hdr->rpc_list)) {
                struct nfs_read_data *data = list_first_entry(&hdr->rpc_list,
                                struct nfs_read_data, list);
                list_del(&data->list);
                nfs_readdata_release(data);
        }
        desc->pg_completion_ops->error_cleanup(&desc->pg_list);
}

/*
 * Generate multiple requests to fill a single page.
 *
 * We optimize to reduce the number of read operations on the wire.  If we
 * detect that we're reading a page, or an area of a page, that is past the
 * end of file, we do not generate NFS read operations but just clear the
 * parts of the page that would have come back zero from the server anyway.
 *
 * We rely on the cached value of i_size to make this determination; another
 * client can fill pages on the server past our cached end-of-file, but we
 * won't see the new data until our attribute cache is updated.  This is more
 * or less conventional NFS client behavior.
 */
static int nfs_pagein_multi(struct nfs_pageio_descriptor *desc,
                            struct nfs_pgio_header *hdr)
{
        struct nfs_page *req = hdr->req;
        struct page *page = req->wb_page;
        struct nfs_read_data *data;
        size_t rsize = desc->pg_bsize, nbytes;
        unsigned int offset;

        offset = 0;
        nbytes = desc->pg_count;
        do {
                size_t len = min(nbytes,rsize);

                data = nfs_readdata_alloc(hdr, 1);
                if (!data) {
                        nfs_pagein_error(desc, hdr);
                        return -ENOMEM;
                }
                data->pages.pagevec[0] = page;
                nfs_read_rpcsetup(data, len, offset);
                list_add(&data->list, &hdr->rpc_list);
                nbytes -= len;
                offset += len;
        } while (nbytes != 0);

        nfs_list_remove_request(req);
        nfs_list_add_request(req, &hdr->pages);
        desc->pg_rpc_callops = &nfs_read_common_ops;
        return 0;
}

static int nfs_pagein_one(struct nfs_pageio_descriptor *desc,
                          struct nfs_pgio_header *hdr)
{
        struct nfs_page         *req;
        struct page             **pages;
        struct nfs_read_data    *data;
        struct list_head *head = &desc->pg_list;

        data = nfs_readdata_alloc(hdr, nfs_page_array_len(desc->pg_base,
                                                          desc->pg_count));
        if (!data) {
                nfs_pagein_error(desc, hdr);
                return -ENOMEM;
        }

        pages = data->pages.pagevec;
        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_list_add_request(req, &hdr->pages);
                *pages++ = req->wb_page;
        }

        nfs_read_rpcsetup(data, desc->pg_count, 0);
        list_add(&data->list, &hdr->rpc_list);
        desc->pg_rpc_callops = &nfs_read_common_ops;
        return 0;
}

int nfs_generic_pagein(struct nfs_pageio_descriptor *desc,
                       struct nfs_pgio_header *hdr)
{
        if (desc->pg_bsize < PAGE_CACHE_SIZE)
                return nfs_pagein_multi(desc, hdr);
        return nfs_pagein_one(desc, hdr);
}
EXPORT_SYMBOL_GPL(nfs_generic_pagein);

static int nfs_generic_pg_readpages(struct nfs_pageio_descriptor *desc)
{
        struct nfs_read_header *rhdr;
        struct nfs_pgio_header *hdr;
        int ret;

        rhdr = nfs_readhdr_alloc();
        if (!rhdr) {
                desc->pg_completion_ops->error_cleanup(&desc->pg_list);
                return -ENOMEM;
        }
        hdr = &rhdr->header;
        nfs_pgheader_init(desc, hdr, nfs_readhdr_free);
        atomic_inc(&hdr->refcnt);
        ret = nfs_generic_pagein(desc, hdr);
        if (ret == 0)
                ret = nfs_do_multiple_reads(&hdr->rpc_list,
                                            desc->pg_rpc_callops);
        if (atomic_dec_and_test(&hdr->refcnt))
                hdr->completion_ops->completion(hdr);
        return ret;
}

static const struct nfs_pageio_ops nfs_pageio_read_ops = {
        .pg_test = nfs_generic_pg_test,
        .pg_doio = nfs_generic_pg_readpages,
};

/*
 * This is the callback from RPC telling us whether a reply was
 * received or some error occurred (timeout or socket shutdown).
 */
int nfs_readpage_result(struct rpc_task *task, struct nfs_read_data *data)
{
        struct inode *inode = data->header->inode;
        int status;

        dprintk("NFS: %s: %5u, (status %d)\n", __func__, task->tk_pid,
                        task->tk_status);

        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_read_data *data)
{
        struct nfs_readargs *argp = &data->args;
        struct nfs_readres *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_common(struct rpc_task *task, void *calldata)
{
        struct nfs_read_data *data = calldata;
        struct nfs_pgio_header *hdr = data->header;

        /* Note the only returns of nfs_readpage_result are 0 and -EAGAIN */
        if (nfs_readpage_result(task, data) != 0)
                return;
        if (task->tk_status < 0)
                nfs_set_pgio_error(hdr, task->tk_status, data->args.offset);
        else 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);
}

static void nfs_readpage_release_common(void *calldata)
{
        nfs_readdata_release(calldata);
}

void nfs_read_prepare(struct rpc_task *task, void *calldata)
{
        struct nfs_read_data *data = calldata;
        NFS_PROTO(data->header->inode)->read_rpc_prepare(task, data);
        if (unlikely(test_bit(NFS_CONTEXT_BAD, &data->args.context->flags)))
                rpc_exit(task, -EIO);
}

static const struct rpc_call_ops nfs_read_common_ops = {
        .rpc_call_prepare = nfs_read_prepare,
        .rpc_call_done = nfs_readpage_result_common,
        .rpc_release = nfs_readpage_release_common,
};

/*
 * 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 inode *inode = page_file_mapping(page)->host;
        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, inode, page, 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/%Ld %d)\n",
                        inode->i_sb->s_id,
                        (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_PROTO(inode)->read_pageio_init(&pgio, inode, &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_read_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);
}