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>

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index b9800c7a1d5db25764b0871af204ab914d749801..5396b8a3028ffc6691ca6f37fd5462c3e4d5911f 100644 (file)
--- 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 =