vhost/scsi: Add ANY_LAYOUT iov -> sgl mapping prerequisites

This patch adds ANY_LAYOUT prerequisites logic for accepting a set of
protection + data payloads via iov_iter.  Also includes helpers for
calcuating SGLs + invoking vhost_scsi_map_to_sgl() with a known number
of iovecs.

Required by ANY_LAYOUT processing when struct iovec may be offset into
the first outgoing virtio-scsi request header.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 93 insertions, 0 deletions

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index b9800c7a1d5d..5396b8a3028f 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -914,6 +914,99 @@ vhost_scsi_map_iov_to_prot(struct tcm_vhost_cmd *cmd,
         return 0;
 }
 
+static int
+vhost_scsi_calc_sgls(struct iov_iter *iter, size_t bytes, int max_sgls)
+{
+        int sgl_count = 0;
+
+        if (!iter || !iter->iov) {
+                pr_err("%s: iter->iov is NULL, but expected bytes: %zu"
+                       " present\n", __func__, bytes);
+                return -EINVAL;
+        }
+
+        sgl_count = iov_iter_npages(iter, 0xffff);
+        if (sgl_count > max_sgls) {
+                pr_err("%s: requested sgl_count: %d exceeds pre-allocated"
+                       " max_sgls: %d\n", __func__, sgl_count, max_sgls);
+                return -EINVAL;
+        }
+        return sgl_count;
+}
+
+static int
+vhost_scsi_iov_to_sgl(struct tcm_vhost_cmd *cmd, bool write,
+                      struct iov_iter *iter, struct scatterlist *sg,
+                      int sg_count)
+{
+        size_t off = iter->iov_offset;
+        int i, ret;
+
+        for (i = 0; i < iter->nr_segs; i++) {
+                void __user *base = iter->iov[i].iov_base + off;
+                size_t len = iter->iov[i].iov_len - off;
+
+                ret = vhost_scsi_map_to_sgl(cmd, base, len, sg, write);
+                if (ret < 0) {
+                        for (i = 0; i < sg_count; i++) {
+                                struct page *page = sg_page(&sg[i]);
+                                if (page)
+                                        put_page(page);
+                        }
+                        return ret;
+                }
+                sg += ret;
+                off = 0;
+        }
+        return 0;
+}
+
+static int
+vhost_scsi_mapal(struct tcm_vhost_cmd *cmd,
+                 size_t prot_bytes, struct iov_iter *prot_iter,
+                 size_t data_bytes, struct iov_iter *data_iter)
+{
+        int sgl_count, ret;
+        bool write = (cmd->tvc_data_direction == DMA_FROM_DEVICE);
+
+        if (prot_bytes) {
+                sgl_count = vhost_scsi_calc_sgls(prot_iter, prot_bytes,
+                                                 TCM_VHOST_PREALLOC_PROT_SGLS);
+                if (sgl_count < 0)
+                        return sgl_count;
+
+                sg_init_table(cmd->tvc_prot_sgl, sgl_count);
+                cmd->tvc_prot_sgl_count = sgl_count;
+                pr_debug("%s prot_sg %p prot_sgl_count %u\n", __func__,
+                         cmd->tvc_prot_sgl, cmd->tvc_prot_sgl_count);
+
+                ret = vhost_scsi_iov_to_sgl(cmd, write, prot_iter,
+                                            cmd->tvc_prot_sgl,
+                                            cmd->tvc_prot_sgl_count);
+                if (ret < 0) {
+                        cmd->tvc_prot_sgl_count = 0;
+                        return ret;
+                }
+        }
+        sgl_count = vhost_scsi_calc_sgls(data_iter, data_bytes,
+                                         TCM_VHOST_PREALLOC_SGLS);
+        if (sgl_count < 0)
+                return sgl_count;
+
+        sg_init_table(cmd->tvc_sgl, sgl_count);
+        cmd->tvc_sgl_count = sgl_count;
+        pr_debug("%s data_sg %p data_sgl_count %u\n", __func__,
+                  cmd->tvc_sgl, cmd->tvc_sgl_count);
+
+        ret = vhost_scsi_iov_to_sgl(cmd, write, data_iter,
+                                    cmd->tvc_sgl, cmd->tvc_sgl_count);
+        if (ret < 0) {
+                cmd->tvc_sgl_count = 0;
+                return ret;
+        }
+        return 0;
+}
+
 static void tcm_vhost_submission_work(struct work_struct *work)
 {
         struct tcm_vhost_cmd *cmd =