RDS: RDMA support

Some transports may support RDMA features. This handles the
non-transport-specific parts, like pinning user pages and
tracking mapped regions.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 679 insertions, 0 deletions

diff --git a/net/rds/rdma.c b/net/rds/rdma.c
new file mode 100644
index 000000000000..eaeeb91e1119
--- /dev/null
+++ b/net/rds/rdma.c
@@ -0,0 +1,679 @@
+/*
+ * Copyright (c) 2007 Oracle.  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
+ * OpenIB.org BSD 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.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/pagemap.h>
+#include <linux/rbtree.h>
+#include <linux/dma-mapping.h> /* for DMA_*_DEVICE */
+
+#include "rdma.h"
+
+/*
+ * XXX
+ *  - build with sparse
+ *  - should we limit the size of a mr region?  let transport return failure?
+ *  - should we detect duplicate keys on a socket?  hmm.
+ *  - an rdma is an mlock, apply rlimit?
+ */
+
+/*
+ * get the number of pages by looking at the page indices that the start and
+ * end addresses fall in.
+ *
+ * Returns 0 if the vec is invalid.  It is invalid if the number of bytes
+ * causes the address to wrap or overflows an unsigned int.  This comes
+ * from being stored in the 'length' member of 'struct scatterlist'.
+ */
+static unsigned int rds_pages_in_vec(struct rds_iovec *vec)
+{
+        if ((vec->addr + vec->bytes <= vec->addr) ||
+            (vec->bytes > (u64)UINT_MAX))
+                return 0;
+
+        return ((vec->addr + vec->bytes + PAGE_SIZE - 1) >> PAGE_SHIFT) -
+                (vec->addr >> PAGE_SHIFT);
+}
+
+static struct rds_mr *rds_mr_tree_walk(struct rb_root *root, u64 key,
+                                       struct rds_mr *insert)
+{
+        struct rb_node **p = &root->rb_node;
+        struct rb_node *parent = NULL;
+        struct rds_mr *mr;
+
+        while (*p) {
+                parent = *p;
+                mr = rb_entry(parent, struct rds_mr, r_rb_node);
+
+                if (key < mr->r_key)
+                        p = &(*p)->rb_left;
+                else if (key > mr->r_key)
+                        p = &(*p)->rb_right;
+                else
+                        return mr;
+        }
+
+        if (insert) {
+                rb_link_node(&insert->r_rb_node, parent, p);
+                rb_insert_color(&insert->r_rb_node, root);
+                atomic_inc(&insert->r_refcount);
+        }
+        return NULL;
+}
+
+/*
+ * Destroy the transport-specific part of a MR.
+ */
+static void rds_destroy_mr(struct rds_mr *mr)
+{
+        struct rds_sock *rs = mr->r_sock;
+        void *trans_private = NULL;
+        unsigned long flags;
+
+        rdsdebug("RDS: destroy mr key is %x refcnt %u\n",
+                        mr->r_key, atomic_read(&mr->r_refcount));
+
+        if (test_and_set_bit(RDS_MR_DEAD, &mr->r_state))
+                return;
+
+        spin_lock_irqsave(&rs->rs_rdma_lock, flags);
+        if (!RB_EMPTY_NODE(&mr->r_rb_node))
+                rb_erase(&mr->r_rb_node, &rs->rs_rdma_keys);
+        trans_private = mr->r_trans_private;
+        mr->r_trans_private = NULL;
+        spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
+
+        if (trans_private)
+                mr->r_trans->free_mr(trans_private, mr->r_invalidate);
+}
+
+void __rds_put_mr_final(struct rds_mr *mr)
+{
+        rds_destroy_mr(mr);
+        kfree(mr);
+}
+
+/*
+ * By the time this is called we can't have any more ioctls called on
+ * the socket so we don't need to worry about racing with others.
+ */
+void rds_rdma_drop_keys(struct rds_sock *rs)
+{
+        struct rds_mr *mr;
+        struct rb_node *node;
+
+        /* Release any MRs associated with this socket */
+        while ((node = rb_first(&rs->rs_rdma_keys))) {
+                mr = container_of(node, struct rds_mr, r_rb_node);
+                if (mr->r_trans == rs->rs_transport)
+                        mr->r_invalidate = 0;
+                rds_mr_put(mr);
+        }
+
+        if (rs->rs_transport && rs->rs_transport->flush_mrs)
+                rs->rs_transport->flush_mrs();
+}
+
+/*
+ * Helper function to pin user pages.
+ */
+static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages,
+                        struct page **pages, int write)
+{
+        int ret;
+
+        down_read(&current->mm->mmap_sem);
+        ret = get_user_pages(current, current->mm, user_addr,
+                             nr_pages, write, 0, pages, NULL);
+        up_read(&current->mm->mmap_sem);
+
+        if (0 <= ret && (unsigned) ret < nr_pages) {
+                while (ret--)
+                        put_page(pages[ret]);
+                ret = -EFAULT;
+        }
+
+        return ret;
+}
+
+static int __rds_rdma_map(struct rds_sock *rs, struct rds_get_mr_args *args,
+                                u64 *cookie_ret, struct rds_mr **mr_ret)
+{
+        struct rds_mr *mr = NULL, *found;
+        unsigned int nr_pages;
+        struct page **pages = NULL;
+        struct scatterlist *sg;
+        void *trans_private;
+        unsigned long flags;
+        rds_rdma_cookie_t cookie;
+        unsigned int nents;
+        long i;
+        int ret;
+
+        if (rs->rs_bound_addr == 0) {
+                ret = -ENOTCONN; /* XXX not a great errno */
+                goto out;
+        }
+
+        if (rs->rs_transport->get_mr == NULL) {
+                ret = -EOPNOTSUPP;
+                goto out;
+        }
+
+        nr_pages = rds_pages_in_vec(&args->vec);
+        if (nr_pages == 0) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        rdsdebug("RDS: get_mr addr %llx len %llu nr_pages %u\n",
+                args->vec.addr, args->vec.bytes, nr_pages);
+
+        /* XXX clamp nr_pages to limit the size of this alloc? */
+        pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);
+        if (pages == NULL) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        mr = kzalloc(sizeof(struct rds_mr), GFP_KERNEL);
+        if (mr == NULL) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        atomic_set(&mr->r_refcount, 1);
+        RB_CLEAR_NODE(&mr->r_rb_node);
+        mr->r_trans = rs->rs_transport;
+        mr->r_sock = rs;
+
+        if (args->flags & RDS_RDMA_USE_ONCE)
+                mr->r_use_once = 1;
+        if (args->flags & RDS_RDMA_INVALIDATE)
+                mr->r_invalidate = 1;
+        if (args->flags & RDS_RDMA_READWRITE)
+                mr->r_write = 1;
+
+        /*
+         * Pin the pages that make up the user buffer and transfer the page
+         * pointers to the mr's sg array.  We check to see if we've mapped
+         * the whole region after transferring the partial page references
+         * to the sg array so that we can have one page ref cleanup path.
+         *
+         * For now we have no flag that tells us whether the mapping is
+         * r/o or r/w. We need to assume r/w, or we'll do a lot of RDMA to
+         * the zero page.
+         */
+        ret = rds_pin_pages(args->vec.addr & PAGE_MASK, nr_pages, pages, 1);
+        if (ret < 0)
+                goto out;
+
+        nents = ret;
+        sg = kcalloc(nents, sizeof(*sg), GFP_KERNEL);
+        if (sg == NULL) {
+                ret = -ENOMEM;
+                goto out;
+        }
+        WARN_ON(!nents);
+        sg_init_table(sg, nents);
+
+        /* Stick all pages into the scatterlist */
+        for (i = 0 ; i < nents; i++)
+                sg_set_page(&sg[i], pages[i], PAGE_SIZE, 0);
+
+        rdsdebug("RDS: trans_private nents is %u\n", nents);
+
+        /* Obtain a transport specific MR. If this succeeds, the
+         * s/g list is now owned by the MR.
+         * Note that dma_map() implies that pending writes are
+         * flushed to RAM, so no dma_sync is needed here. */
+        trans_private = rs->rs_transport->get_mr(sg, nents, rs,
+                                                 &mr->r_key);
+
+        if (IS_ERR(trans_private)) {
+                for (i = 0 ; i < nents; i++)
+                        put_page(sg_page(&sg[i]));
+                kfree(sg);
+                ret = PTR_ERR(trans_private);
+                goto out;
+        }
+
+        mr->r_trans_private = trans_private;
+
+        rdsdebug("RDS: get_mr put_user key is %x cookie_addr %p\n",
+               mr->r_key, (void *)(unsigned long) args->cookie_addr);
+
+        /* The user may pass us an unaligned address, but we can only
+         * map page aligned regions. So we keep the offset, and build
+         * a 64bit cookie containing <R_Key, offset> and pass that
+         * around. */
+        cookie = rds_rdma_make_cookie(mr->r_key, args->vec.addr & ~PAGE_MASK);
+        if (cookie_ret)
+                *cookie_ret = cookie;
+
+        if (args->cookie_addr && put_user(cookie, (u64 __user *)(unsigned long) args->cookie_addr)) {
+                ret = -EFAULT;
+                goto out;
+        }
+
+        /* Inserting the new MR into the rbtree bumps its
+         * reference count. */
+        spin_lock_irqsave(&rs->rs_rdma_lock, flags);
+        found = rds_mr_tree_walk(&rs->rs_rdma_keys, mr->r_key, mr);
+        spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
+
+        BUG_ON(found && found != mr);
+
+        rdsdebug("RDS: get_mr key is %x\n", mr->r_key);
+        if (mr_ret) {
+                atomic_inc(&mr->r_refcount);
+                *mr_ret = mr;
+        }
+
+        ret = 0;
+out:
+        kfree(pages);
+        if (mr)
+                rds_mr_put(mr);
+        return ret;
+}
+
+int rds_get_mr(struct rds_sock *rs, char __user *optval, int optlen)
+{
+        struct rds_get_mr_args args;
+
+        if (optlen != sizeof(struct rds_get_mr_args))
+                return -EINVAL;
+
+        if (copy_from_user(&args, (struct rds_get_mr_args __user *)optval,
+                           sizeof(struct rds_get_mr_args)))
+                return -EFAULT;
+
+        return __rds_rdma_map(rs, &args, NULL, NULL);
+}
+
+/*
+ * Free the MR indicated by the given R_Key
+ */
+int rds_free_mr(struct rds_sock *rs, char __user *optval, int optlen)
+{
+        struct rds_free_mr_args args;
+        struct rds_mr *mr;
+        unsigned long flags;
+
+        if (optlen != sizeof(struct rds_free_mr_args))
+                return -EINVAL;
+
+        if (copy_from_user(&args, (struct rds_free_mr_args __user *)optval,
+                           sizeof(struct rds_free_mr_args)))
+                return -EFAULT;
+
+        /* Special case - a null cookie means flush all unused MRs */
+        if (args.cookie == 0) {
+                if (!rs->rs_transport || !rs->rs_transport->flush_mrs)
+                        return -EINVAL;
+                rs->rs_transport->flush_mrs();
+                return 0;
+        }
+
+        /* Look up the MR given its R_key and remove it from the rbtree
+         * so nobody else finds it.
+         * This should also prevent races with rds_rdma_unuse.
+         */
+        spin_lock_irqsave(&rs->rs_rdma_lock, flags);
+        mr = rds_mr_tree_walk(&rs->rs_rdma_keys, rds_rdma_cookie_key(args.cookie), NULL);
+        if (mr) {
+                rb_erase(&mr->r_rb_node, &rs->rs_rdma_keys);
+                RB_CLEAR_NODE(&mr->r_rb_node);
+                if (args.flags & RDS_RDMA_INVALIDATE)
+                        mr->r_invalidate = 1;
+        }
+        spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
+
+        if (!mr)
+                return -EINVAL;
+
+        /*
+         * call rds_destroy_mr() ourselves so that we're sure it's done by the time
+         * we return.  If we let rds_mr_put() do it it might not happen until
+         * someone else drops their ref.
+         */
+        rds_destroy_mr(mr);
+        rds_mr_put(mr);
+        return 0;
+}
+
+/*
+ * This is called when we receive an extension header that
+ * tells us this MR was used. It allows us to implement
+ * use_once semantics
+ */
+void rds_rdma_unuse(struct rds_sock *rs, u32 r_key, int force)
+{
+        struct rds_mr *mr;
+        unsigned long flags;
+        int zot_me = 0;
+
+        spin_lock_irqsave(&rs->rs_rdma_lock, flags);
+        mr = rds_mr_tree_walk(&rs->rs_rdma_keys, r_key, NULL);
+        if (mr && (mr->r_use_once || force)) {
+                rb_erase(&mr->r_rb_node, &rs->rs_rdma_keys);
+                RB_CLEAR_NODE(&mr->r_rb_node);
+                zot_me = 1;
+        } else if (mr)
+                atomic_inc(&mr->r_refcount);
+        spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
+
+        /* May have to issue a dma_sync on this memory region.
+         * Note we could avoid this if the operation was a RDMA READ,
+         * but at this point we can't tell. */
+        if (mr != NULL) {
+                if (mr->r_trans->sync_mr)
+                        mr->r_trans->sync_mr(mr->r_trans_private, DMA_FROM_DEVICE);
+
+                /* If the MR was marked as invalidate, this will
+                 * trigger an async flush. */
+                if (zot_me)
+                        rds_destroy_mr(mr);
+                rds_mr_put(mr);
+        }
+}
+
+void rds_rdma_free_op(struct rds_rdma_op *ro)
+{
+        unsigned int i;
+
+        for (i = 0; i < ro->r_nents; i++) {
+                struct page *page = sg_page(&ro->r_sg[i]);
+
+                /* Mark page dirty if it was possibly modified, which
+                 * is the case for a RDMA_READ which copies from remote
+                 * to local memory */
+                if (!ro->r_write)
+                        set_page_dirty(page);
+                put_page(page);
+        }
+
+        kfree(ro->r_notifier);
+        kfree(ro);
+}
+
+/*
+ * args is a pointer to an in-kernel copy in the sendmsg cmsg.
+ */
+static struct rds_rdma_op *rds_rdma_prepare(struct rds_sock *rs,
+                                            struct rds_rdma_args *args)
+{
+        struct rds_iovec vec;
+        struct rds_rdma_op *op = NULL;
+        unsigned int nr_pages;
+        unsigned int max_pages;
+        unsigned int nr_bytes;
+        struct page **pages = NULL;
+        struct rds_iovec __user *local_vec;
+        struct scatterlist *sg;
+        unsigned int nr;
+        unsigned int i, j;
+        int ret;
+
+
+        if (rs->rs_bound_addr == 0) {
+                ret = -ENOTCONN; /* XXX not a great errno */
+                goto out;
+        }
+
+        if (args->nr_local > (u64)UINT_MAX) {
+                ret = -EMSGSIZE;
+                goto out;
+        }
+
+        nr_pages = 0;
+        max_pages = 0;
+
+        local_vec = (struct rds_iovec __user *)(unsigned long) args->local_vec_addr;
+
+        /* figure out the number of pages in the vector */
+        for (i = 0; i < args->nr_local; i++) {
+                if (copy_from_user(&vec, &local_vec[i],
+                                   sizeof(struct rds_iovec))) {
+                        ret = -EFAULT;
+                        goto out;
+                }
+
+                nr = rds_pages_in_vec(&vec);
+                if (nr == 0) {
+                        ret = -EINVAL;
+                        goto out;
+                }
+
+                max_pages = max(nr, max_pages);
+                nr_pages += nr;
+        }
+
+        pages = kcalloc(max_pages, sizeof(struct page *), GFP_KERNEL);
+        if (pages == NULL) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        op = kzalloc(offsetof(struct rds_rdma_op, r_sg[nr_pages]), GFP_KERNEL);
+        if (op == NULL) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        op->r_write = !!(args->flags & RDS_RDMA_READWRITE);
+        op->r_fence = !!(args->flags & RDS_RDMA_FENCE);
+        op->r_notify = !!(args->flags & RDS_RDMA_NOTIFY_ME);
+        op->r_recverr = rs->rs_recverr;
+        WARN_ON(!nr_pages);
+        sg_init_table(op->r_sg, nr_pages);
+
+        if (op->r_notify || op->r_recverr) {
+                /* We allocate an uninitialized notifier here, because
+                 * we don't want to do that in the completion handler. We
+                 * would have to use GFP_ATOMIC there, and don't want to deal
+                 * with failed allocations.
+                 */
+                op->r_notifier = kmalloc(sizeof(struct rds_notifier), GFP_KERNEL);
+                if (!op->r_notifier) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
+                op->r_notifier->n_user_token = args->user_token;
+                op->r_notifier->n_status = RDS_RDMA_SUCCESS;
+        }
+
+        /* The cookie contains the R_Key of the remote memory region, and
+         * optionally an offset into it. This is how we implement RDMA into
+         * unaligned memory.
+         * When setting up the RDMA, we need to add that offset to the
+         * destination address (which is really an offset into the MR)
+         * FIXME: We may want to move this into ib_rdma.c
+         */
+        op->r_key = rds_rdma_cookie_key(args->cookie);
+        op->r_remote_addr = args->remote_vec.addr + rds_rdma_cookie_offset(args->cookie);
+
+        nr_bytes = 0;
+
+        rdsdebug("RDS: rdma prepare nr_local %llu rva %llx rkey %x\n",
+               (unsigned long long)args->nr_local,
+               (unsigned long long)args->remote_vec.addr,
+               op->r_key);
+
+        for (i = 0; i < args->nr_local; i++) {
+                if (copy_from_user(&vec, &local_vec[i],
+                                   sizeof(struct rds_iovec))) {
+                        ret = -EFAULT;
+                        goto out;
+                }
+
+                nr = rds_pages_in_vec(&vec);
+                if (nr == 0) {
+                        ret = -EINVAL;
+                        goto out;
+                }
+
+                rs->rs_user_addr = vec.addr;
+                rs->rs_user_bytes = vec.bytes;
+
+                /* did the user change the vec under us? */
+                if (nr > max_pages || op->r_nents + nr > nr_pages) {
+                        ret = -EINVAL;
+                        goto out;
+                }
+                /* If it's a WRITE operation, we want to pin the pages for reading.
+                 * If it's a READ operation, we need to pin the pages for writing.
+                 */
+                ret = rds_pin_pages(vec.addr & PAGE_MASK, nr, pages, !op->r_write);
+                if (ret < 0)
+                        goto out;
+
+                rdsdebug("RDS: nr_bytes %u nr %u vec.bytes %llu vec.addr %llx\n",
+                       nr_bytes, nr, vec.bytes, vec.addr);
+
+                nr_bytes += vec.bytes;
+
+                for (j = 0; j < nr; j++) {
+                        unsigned int offset = vec.addr & ~PAGE_MASK;
+
+                        sg = &op->r_sg[op->r_nents + j];
+                        sg_set_page(sg, pages[j],
+                                        min_t(unsigned int, vec.bytes, PAGE_SIZE - offset),
+                                        offset);
+
+                        rdsdebug("RDS: sg->offset %x sg->len %x vec.addr %llx vec.bytes %llu\n",
+                               sg->offset, sg->length, vec.addr, vec.bytes);
+
+                        vec.addr += sg->length;
+                        vec.bytes -= sg->length;
+                }
+
+                op->r_nents += nr;
+        }
+
+
+        if (nr_bytes > args->remote_vec.bytes) {
+                rdsdebug("RDS nr_bytes %u remote_bytes %u do not match\n",
+                                nr_bytes,
+                                (unsigned int) args->remote_vec.bytes);
+                ret = -EINVAL;
+                goto out;
+        }
+        op->r_bytes = nr_bytes;
+
+        ret = 0;
+out:
+        kfree(pages);
+        if (ret) {
+                if (op)
+                        rds_rdma_free_op(op);
+                op = ERR_PTR(ret);
+        }
+        return op;
+}
+
+/*
+ * The application asks for a RDMA transfer.
+ * Extract all arguments and set up the rdma_op
+ */
+int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
+                          struct cmsghdr *cmsg)
+{
+        struct rds_rdma_op *op;
+
+        if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct rds_rdma_args))
+         || rm->m_rdma_op != NULL)
+                return -EINVAL;
+
+        op = rds_rdma_prepare(rs, CMSG_DATA(cmsg));
+        if (IS_ERR(op))
+                return PTR_ERR(op);
+        rds_stats_inc(s_send_rdma);
+        rm->m_rdma_op = op;
+        return 0;
+}
+
+/*
+ * The application wants us to pass an RDMA destination (aka MR)
+ * to the remote
+ */
+int rds_cmsg_rdma_dest(struct rds_sock *rs, struct rds_message *rm,
+                          struct cmsghdr *cmsg)
+{
+        unsigned long flags;
+        struct rds_mr *mr;
+        u32 r_key;
+        int err = 0;
+
+        if (cmsg->cmsg_len < CMSG_LEN(sizeof(rds_rdma_cookie_t))
+         || rm->m_rdma_cookie != 0)
+                return -EINVAL;
+
+        memcpy(&rm->m_rdma_cookie, CMSG_DATA(cmsg), sizeof(rm->m_rdma_cookie));
+
+        /* We are reusing a previously mapped MR here. Most likely, the
+         * application has written to the buffer, so we need to explicitly
+         * flush those writes to RAM. Otherwise the HCA may not see them
+         * when doing a DMA from that buffer.
+         */
+        r_key = rds_rdma_cookie_key(rm->m_rdma_cookie);
+
+        spin_lock_irqsave(&rs->rs_rdma_lock, flags);
+        mr = rds_mr_tree_walk(&rs->rs_rdma_keys, r_key, NULL);
+        if (mr == NULL)
+                err = -EINVAL;  /* invalid r_key */
+        else
+                atomic_inc(&mr->r_refcount);
+        spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
+
+        if (mr) {
+                mr->r_trans->sync_mr(mr->r_trans_private, DMA_TO_DEVICE);
+                rm->m_rdma_mr = mr;
+        }
+        return err;
+}
+
+/*
+ * The application passes us an address range it wants to enable RDMA
+ * to/from. We map the area, and save the <R_Key,offset> pair
+ * in rm->m_rdma_cookie. This causes it to be sent along to the peer
+ * in an extension header.
+ */
+int rds_cmsg_rdma_map(struct rds_sock *rs, struct rds_message *rm,
+                          struct cmsghdr *cmsg)
+{
+        if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct rds_get_mr_args))
+         || rm->m_rdma_cookie != 0)
+                return -EINVAL;
+
+        return __rds_rdma_map(rs, CMSG_DATA(cmsg), &rm->m_rdma_cookie, &rm->m_rdma_mr);
+}