/*
 * 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_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, GFP_KERNEL);
}
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)
{
        struct inode *inode = d_inode(req->wb_context->dentry);

        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_page_group_sync_on_bit(req, PG_UNLOCKPAGE)) {
                if (PageUptodate(req->wb_page))
                        nfs_readpage_to_fscache(inode, req->wb_page, 0);

                unlock_page(req->wb_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, NULL, 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);
        }
        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;

        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_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);
}

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_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);

        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_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;
        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 bound;

                bound = hdr->args.offset + hdr->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 (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;
        }

        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_SIZE)
                zero_user_segment(page, len, PAGE_SIZE);
        if (!nfs_pageio_add_request(desc->pgio, new)) {
                nfs_list_remove_request(new);
                nfs_readpage_release(new);
                error = desc->pgio->pg_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,
};