/*
 * Copyright (c) 2016, 2017 Oracle. All rights reserved.
 * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
 * Copyright (c) 2005-2006 Network Appliance, Inc. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the BSD-type
 * license below:
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *      Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *      Redistributions in binary form must reproduce the above
 *      copyright notice, this list of conditions and the following
 *      disclaimer in the documentation and/or other materials provided
 *      with the distribution.
 *
 *      Neither the name of the Network Appliance, Inc. nor the names of
 *      its contributors may be used to endorse or promote products
 *      derived from this software without specific prior written
 *      permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Author: Tom Tucker <tom@opengridcomputing.com>
 */

/* Operation
 *
 * The main entry point is svc_rdma_recvfrom. This is called from
 * svc_recv when the transport indicates there is incoming data to
 * be read. "Data Ready" is signaled when an RDMA Receive completes,
 * or when a set of RDMA Reads complete.
 *
 * An svc_rqst is passed in. This structure contains an array of
 * free pages (rq_pages) that will contain the incoming RPC message.
 *
 * Short messages are moved directly into svc_rqst::rq_arg, and
 * the RPC Call is ready to be processed by the Upper Layer.
 * svc_rdma_recvfrom returns the length of the RPC Call message,
 * completing the reception of the RPC Call.
 *
 * However, when an incoming message has Read chunks,
 * svc_rdma_recvfrom must post RDMA Reads to pull the RPC Call's
 * data payload from the client. svc_rdma_recvfrom sets up the
 * RDMA Reads using pages in svc_rqst::rq_pages, which are
 * transferred to an svc_rdma_op_ctxt for the duration of the
 * I/O. svc_rdma_recvfrom then returns zero, since the RPC message
 * is still not yet ready.
 *
 * When the Read chunk payloads have become available on the
 * server, "Data Ready" is raised again, and svc_recv calls
 * svc_rdma_recvfrom again. This second call may use a different
 * svc_rqst than the first one, thus any information that needs
 * to be preserved across these two calls is kept in an
 * svc_rdma_op_ctxt.
 *
 * The second call to svc_rdma_recvfrom performs final assembly
 * of the RPC Call message, using the RDMA Read sink pages kept in
 * the svc_rdma_op_ctxt. The xdr_buf is copied from the
 * svc_rdma_op_ctxt to the second svc_rqst. The second call returns
 * the length of the completed RPC Call message.
 *
 * Page Management
 *
 * Pages under I/O must be transferred from the first svc_rqst to an
 * svc_rdma_op_ctxt before the first svc_rdma_recvfrom call returns.
 *
 * The first svc_rqst supplies pages for RDMA Reads. These are moved
 * from rqstp::rq_pages into ctxt::pages. The consumed elements of
 * the rq_pages array are set to NULL and refilled with the first
 * svc_rdma_recvfrom call returns.
 *
 * During the second svc_rdma_recvfrom call, RDMA Read sink pages
 * are transferred from the svc_rdma_op_ctxt to the second svc_rqst
 * (see rdma_read_complete() below).
 */

#include <asm/unaligned.h>
#include <rdma/ib_verbs.h>
#include <rdma/rdma_cm.h>

#include <linux/spinlock.h>

#include <linux/sunrpc/xdr.h>
#include <linux/sunrpc/debug.h>
#include <linux/sunrpc/rpc_rdma.h>
#include <linux/sunrpc/svc_rdma.h>

#define RPCDBG_FACILITY RPCDBG_SVCXPRT

/*
 * Replace the pages in the rq_argpages array with the pages from the SGE in
 * the RDMA_RECV completion. The SGL should contain full pages up until the
 * last one.
 */
static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
                               struct svc_rdma_op_ctxt *ctxt,
                               u32 byte_count)
{
        struct page *page;
        u32 bc;
        int sge_no;

        /* Swap the page in the SGE with the page in argpages */
        page = ctxt->pages[0];
        put_page(rqstp->rq_pages[0]);
        rqstp->rq_pages[0] = page;

        /* Set up the XDR head */
        rqstp->rq_arg.head[0].iov_base = page_address(page);
        rqstp->rq_arg.head[0].iov_len =
                min_t(size_t, byte_count, ctxt->sge[0].length);
        rqstp->rq_arg.len = byte_count;
        rqstp->rq_arg.buflen = byte_count;

        /* Compute bytes past head in the SGL */
        bc = byte_count - rqstp->rq_arg.head[0].iov_len;

        /* If data remains, store it in the pagelist */
        rqstp->rq_arg.page_len = bc;
        rqstp->rq_arg.page_base = 0;

        sge_no = 1;
        while (bc && sge_no < ctxt->count) {
                page = ctxt->pages[sge_no];
                put_page(rqstp->rq_pages[sge_no]);
                rqstp->rq_pages[sge_no] = page;
                bc -= min_t(u32, bc, ctxt->sge[sge_no].length);
                sge_no++;
        }
        rqstp->rq_respages = &rqstp->rq_pages[sge_no];
        rqstp->rq_next_page = rqstp->rq_respages + 1;

        /* If not all pages were used from the SGL, free the remaining ones */
        bc = sge_no;
        while (sge_no < ctxt->count) {
                page = ctxt->pages[sge_no++];
                put_page(page);
        }
        ctxt->count = bc;

        /* Set up tail */
        rqstp->rq_arg.tail[0].iov_base = NULL;
        rqstp->rq_arg.tail[0].iov_len = 0;
}

/* This accommodates the largest possible Write chunk,
 * in one segment.
 */
#define MAX_BYTES_WRITE_SEG     ((u32)(RPCSVC_MAXPAGES << PAGE_SHIFT))

/* This accommodates the largest possible Position-Zero
 * Read chunk or Reply chunk, in one segment.
 */
#define MAX_BYTES_SPECIAL_SEG   ((u32)((RPCSVC_MAXPAGES + 2) << PAGE_SHIFT))

/* Sanity check the Read list.
 *
 * Implementation limits:
 * - This implementation supports only one Read chunk.
 *
 * Sanity checks:
 * - Read list does not overflow buffer.
 * - Segment size limited by largest NFS data payload.
 *
 * The segment count is limited to how many segments can
 * fit in the transport header without overflowing the
 * buffer. That's about 40 Read segments for a 1KB inline
 * threshold.
 *
 * Returns pointer to the following Write list.
 */
static __be32 *xdr_check_read_list(__be32 *p, const __be32 *end)
{
        u32 position;
        bool first;

        first = true;
        while (*p++ != xdr_zero) {
                if (first) {
                        position = be32_to_cpup(p++);
                        first = false;
                } else if (be32_to_cpup(p++) != position) {
                        return NULL;
                }
                p++;    /* handle */
                if (be32_to_cpup(p++) > MAX_BYTES_SPECIAL_SEG)
                        return NULL;
                p += 2; /* offset */

                if (p > end)
                        return NULL;
        }
        return p;
}

/* The segment count is limited to how many segments can
 * fit in the transport header without overflowing the
 * buffer. That's about 60 Write segments for a 1KB inline
 * threshold.
 */
static __be32 *xdr_check_write_chunk(__be32 *p, const __be32 *end,
                                     u32 maxlen)
{
        u32 i, segcount;

        segcount = be32_to_cpup(p++);
        for (i = 0; i < segcount; i++) {
                p++;    /* handle */
                if (be32_to_cpup(p++) > maxlen)
                        return NULL;
                p += 2; /* offset */

                if (p > end)
                        return NULL;
        }

        return p;
}

/* Sanity check the Write list.
 *
 * Implementation limits:
 * - This implementation supports only one Write chunk.
 *
 * Sanity checks:
 * - Write list does not overflow buffer.
 * - Segment size limited by largest NFS data payload.
 *
 * Returns pointer to the following Reply chunk.
 */
static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end)
{
        u32 chcount;

        chcount = 0;
        while (*p++ != xdr_zero) {
                p = xdr_check_write_chunk(p, end, MAX_BYTES_WRITE_SEG);
                if (!p)
                        return NULL;
                if (chcount++ > 1)
                        return NULL;
        }
        return p;
}

/* Sanity check the Reply chunk.
 *
 * Sanity checks:
 * - Reply chunk does not overflow buffer.
 * - Segment size limited by largest NFS data payload.
 *
 * Returns pointer to the following RPC header.
 */
static __be32 *xdr_check_reply_chunk(__be32 *p, const __be32 *end)
{
        if (*p++ != xdr_zero) {
                p = xdr_check_write_chunk(p, end, MAX_BYTES_SPECIAL_SEG);
                if (!p)
                        return NULL;
        }
        return p;
}

/* On entry, xdr->head[0].iov_base points to first byte in the
 * RPC-over-RDMA header.
 *
 * On successful exit, head[0] points to first byte past the
 * RPC-over-RDMA header. For RDMA_MSG, this is the RPC message.
 * The length of the RPC-over-RDMA header is returned.
 *
 * Assumptions:
 * - The transport header is entirely contained in the head iovec.
 */
static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg)
{
        __be32 *p, *end, *rdma_argp;
        unsigned int hdr_len;
        char *proc;

        /* Verify that there's enough bytes for header + something */
        if (rq_arg->len <= RPCRDMA_HDRLEN_ERR)
                goto out_short;

        rdma_argp = rq_arg->head[0].iov_base;
        if (*(rdma_argp + 1) != rpcrdma_version)
                goto out_version;

        switch (*(rdma_argp + 3)) {
        case rdma_msg:
                proc = "RDMA_MSG";
                break;
        case rdma_nomsg:
                proc = "RDMA_NOMSG";
                break;

        case rdma_done:
                goto out_drop;

        case rdma_error:
                goto out_drop;

        default:
                goto out_proc;
        }

        end = (__be32 *)((unsigned long)rdma_argp + rq_arg->len);
        p = xdr_check_read_list(rdma_argp + 4, end);
        if (!p)
                goto out_inval;
        p = xdr_check_write_list(p, end);
        if (!p)
                goto out_inval;
        p = xdr_check_reply_chunk(p, end);
        if (!p)
                goto out_inval;
        if (p > end)
                goto out_inval;

        rq_arg->head[0].iov_base = p;
        hdr_len = (unsigned long)p - (unsigned long)rdma_argp;
        rq_arg->head[0].iov_len -= hdr_len;
        rq_arg->len -= hdr_len;
        dprintk("svcrdma: received %s request for XID 0x%08x, hdr_len=%u\n",
                proc, be32_to_cpup(rdma_argp), hdr_len);
        return hdr_len;

out_short:
        dprintk("svcrdma: header too short = %d\n", rq_arg->len);
        return -EINVAL;

out_version:
        dprintk("svcrdma: bad xprt version: %u\n",
                be32_to_cpup(rdma_argp + 1));
        return -EPROTONOSUPPORT;

out_drop:
        dprintk("svcrdma: dropping RDMA_DONE/ERROR message\n");
        return 0;

out_proc:
        dprintk("svcrdma: bad rdma procedure (%u)\n",
                be32_to_cpup(rdma_argp + 3));
        return -EINVAL;

out_inval:
        dprintk("svcrdma: failed to parse transport header\n");
        return -EINVAL;
}

static void rdma_read_complete(struct svc_rqst *rqstp,
                               struct svc_rdma_op_ctxt *head)
{
        int page_no;

        /* Copy RPC pages */
        for (page_no = 0; page_no < head->count; page_no++) {
                put_page(rqstp->rq_pages[page_no]);
                rqstp->rq_pages[page_no] = head->pages[page_no];
        }

        /* Point rq_arg.pages past header */
        rqstp->rq_arg.pages = &rqstp->rq_pages[head->hdr_count];
        rqstp->rq_arg.page_len = head->arg.page_len;

        /* rq_respages starts after the last arg page */
        rqstp->rq_respages = &rqstp->rq_pages[page_no];
        rqstp->rq_next_page = rqstp->rq_respages + 1;

        /* Rebuild rq_arg head and tail. */
        rqstp->rq_arg.head[0] = head->arg.head[0];
        rqstp->rq_arg.tail[0] = head->arg.tail[0];
        rqstp->rq_arg.len = head->arg.len;
        rqstp->rq_arg.buflen = head->arg.buflen;
}

static void svc_rdma_send_error(struct svcxprt_rdma *xprt,
                                __be32 *rdma_argp, int status)
{
        struct svc_rdma_op_ctxt *ctxt;
        __be32 *p, *err_msgp;
        unsigned int length;
        struct page *page;
        int ret;

        page = alloc_page(GFP_KERNEL);
        if (!page)
                return;
        err_msgp = page_address(page);

        p = err_msgp;
        *p++ = *rdma_argp;
        *p++ = *(rdma_argp + 1);
        *p++ = xprt->sc_fc_credits;
        *p++ = rdma_error;
        if (status == -EPROTONOSUPPORT) {
                *p++ = err_vers;
                *p++ = rpcrdma_version;
                *p++ = rpcrdma_version;
        } else {
                *p++ = err_chunk;
        }
        length = (unsigned long)p - (unsigned long)err_msgp;

        /* Map transport header; no RPC message payload */
        ctxt = svc_rdma_get_context(xprt);
        ret = svc_rdma_map_reply_hdr(xprt, ctxt, err_msgp, length);
        if (ret) {
                dprintk("svcrdma: Error %d mapping send for protocol error\n",
                        ret);
                return;
        }

        ret = svc_rdma_post_send_wr(xprt, ctxt, 1, 0);
        if (ret) {
                dprintk("svcrdma: Error %d posting send for protocol error\n",
                        ret);
                svc_rdma_unmap_dma(ctxt);
                svc_rdma_put_context(ctxt, 1);
        }
}

/* By convention, backchannel calls arrive via rdma_msg type
 * messages, and never populate the chunk lists. This makes
 * the RPC/RDMA header small and fixed in size, so it is
 * straightforward to check the RPC header's direction field.
 */
static bool svc_rdma_is_backchannel_reply(struct svc_xprt *xprt,
                                          __be32 *rdma_resp)
{
        __be32 *p;

        if (!xprt->xpt_bc_xprt)
                return false;

        p = rdma_resp + 3;
        if (*p++ != rdma_msg)
                return false;

        if (*p++ != xdr_zero)
                return false;
        if (*p++ != xdr_zero)
                return false;
        if (*p++ != xdr_zero)
                return false;

        /* XID sanity */
        if (*p++ != *rdma_resp)
                return false;
        /* call direction */
        if (*p == cpu_to_be32(RPC_CALL))
                return false;

        return true;
}

/**
 * svc_rdma_recvfrom - Receive an RPC call
 * @rqstp: request structure into which to receive an RPC Call
 *
 * Returns:
 *      The positive number of bytes in the RPC Call message,
 *      %0 if there were no Calls ready to return,
 *      %-EINVAL if the Read chunk data is too large,
 *      %-ENOMEM if rdma_rw context pool was exhausted,
 *      %-ENOTCONN if posting failed (connection is lost),
 *      %-EIO if rdma_rw initialization failed (DMA mapping, etc).
 *
 * Called in a loop when XPT_DATA is set. XPT_DATA is cleared only
 * when there are no remaining ctxt's to process.
 *
 * The next ctxt is removed from the "receive" lists.
 *
 * - If the ctxt completes a Read, then finish assembling the Call
 *   message and return the number of bytes in the message.
 *
 * - If the ctxt completes a Receive, then construct the Call
 *   message from the contents of the Receive buffer.
 *
 *   - If there are no Read chunks in this message, then finish
 *     assembling the Call message and return the number of bytes
 *     in the message.
 *
 *   - If there are Read chunks in this message, post Read WRs to
 *     pull that payload and return 0.
 */
int svc_rdma_recvfrom(struct svc_rqst *rqstp)
{
        struct svc_xprt *xprt = rqstp->rq_xprt;
        struct svcxprt_rdma *rdma_xprt =
                container_of(xprt, struct svcxprt_rdma, sc_xprt);
        struct svc_rdma_op_ctxt *ctxt;
        __be32 *p;
        int ret;

        spin_lock(&rdma_xprt->sc_rq_dto_lock);
        if (!list_empty(&rdma_xprt->sc_read_complete_q)) {
                ctxt = list_first_entry(&rdma_xprt->sc_read_complete_q,
                                        struct svc_rdma_op_ctxt, list);
                list_del(&ctxt->list);
                spin_unlock(&rdma_xprt->sc_rq_dto_lock);
                rdma_read_complete(rqstp, ctxt);
                goto complete;
        } else if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
                ctxt = list_first_entry(&rdma_xprt->sc_rq_dto_q,
                                        struct svc_rdma_op_ctxt, list);
                list_del(&ctxt->list);
        } else {
                /* No new incoming requests, terminate the loop */
                clear_bit(XPT_DATA, &xprt->xpt_flags);
                spin_unlock(&rdma_xprt->sc_rq_dto_lock);
                return 0;
        }
        spin_unlock(&rdma_xprt->sc_rq_dto_lock);

        dprintk("svcrdma: recvfrom: ctxt=%p on xprt=%p, rqstp=%p\n",
                ctxt, rdma_xprt, rqstp);
        atomic_inc(&rdma_stat_recv);

        /* Build up the XDR from the receive buffers. */
        rdma_build_arg_xdr(rqstp, ctxt, ctxt->byte_len);

        /* Decode the RDMA header. */
        p = (__be32 *)rqstp->rq_arg.head[0].iov_base;
        ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg);
        if (ret < 0)
                goto out_err;
        if (ret == 0)
                goto out_drop;
        rqstp->rq_xprt_hlen = ret;

        if (svc_rdma_is_backchannel_reply(xprt, p)) {
                ret = svc_rdma_handle_bc_reply(xprt->xpt_bc_xprt, p,
                                               &rqstp->rq_arg);
                svc_rdma_put_context(ctxt, 0);
                return ret;
        }

        p += rpcrdma_fixed_maxsz;
        if (*p != xdr_zero)
                goto out_readchunk;

complete:
        svc_rdma_put_context(ctxt, 0);
        dprintk("svcrdma: recvfrom: xprt=%p, rqstp=%p, rq_arg.len=%u\n",
                rdma_xprt, rqstp, rqstp->rq_arg.len);
        rqstp->rq_prot = IPPROTO_MAX;
        svc_xprt_copy_addrs(rqstp, xprt);
        return rqstp->rq_arg.len;

out_readchunk:
        ret = svc_rdma_recv_read_chunk(rdma_xprt, rqstp, ctxt, p);
        if (ret < 0)
                goto out_postfail;
        return 0;

out_err:
        svc_rdma_send_error(rdma_xprt, p, ret);
        svc_rdma_put_context(ctxt, 0);
        return 0;

out_postfail:
        if (ret == -EINVAL)
                svc_rdma_send_error(rdma_xprt, p, ret);
        svc_rdma_put_context(ctxt, 1);
        return ret;

out_drop:
        svc_rdma_put_context(ctxt, 1);
        return 0;
}