[RFC PATCH 03/10] dma-buf: add support for NET_TX pages

[Mina Almasry]

Used the paged attachment mappings support to create NET_TX pages.
NET_TX pages can be used in the networking transmit path:

1. Create an iov_iter & bio_vec entries to represent this dmabuf.

2. Initialize the bio_vec with the backing dmabuf pages.

Signed-off-by: Mina Almasry <almasrym...@google.com>
---
 drivers/dma-buf/dma-buf.c    | 47 ++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h      |  7 ++++++
 include/uapi/linux/dma-buf.h |  1 +
 3 files changed, 55 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index acb86bf406f4..3ca71297b9b4 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1683,6 +1683,7 @@ static void dma_buf_pages_destroy(struct percpu_ref *ref)
 }
 
 const struct dma_buf_pages_type_ops net_rx_ops;
+const struct dma_buf_pages_type_ops net_tx_ops;
 
 static long dma_buf_create_pages(struct file *file,
                                 struct dma_buf_create_pages_info *create_info)
@@ -1799,6 +1800,9 @@ static long dma_buf_create_pages(struct file *file,
        case DMA_BUF_PAGES_NET_RX:
                priv->type_ops = &net_rx_ops;
                break;
+       case DMA_BUF_PAGES_NET_TX:
+               priv->type_ops = &net_tx_ops;
+               break;
        default:
                err = -EINVAL;
                goto out_put_new_file;
@@ -2140,3 +2144,46 @@ struct page *dma_buf_pages_net_rx_alloc(struct 
dma_buf_pages *priv)
        percpu_ref_get(&priv->pgmap.ref);
        return pg;
 }
+
+/********************************
+ *     dma_buf_pages_net_tx    *
+ ********************************/
+
+static void dma_buf_pages_net_tx_release(struct dma_buf_pages *priv,
+                                        struct file *file)
+{
+       int i;
+       for (i = 0; i < priv->num_pages; i++)
+               put_page(&priv->pages[i]);
+}
+
+static int dma_buf_pages_net_tx_init(struct dma_buf_pages *priv,
+                                    struct file *file)
+{
+       int i;
+       priv->net_tx.tx_bv = kvmalloc_array(priv->num_pages,
+                                           sizeof(struct bio_vec), GFP_KERNEL);
+       if (!priv->net_tx.tx_bv)
+               return -ENOMEM;
+
+       for (i = 0; i < priv->num_pages; i++) {
+               priv->net_tx.tx_bv[i].bv_page = &priv->pages[i];
+               priv->net_tx.tx_bv[i].bv_offset = 0;
+               priv->net_tx.tx_bv[i].bv_len = PAGE_SIZE;
+       }
+       percpu_ref_get_many(&priv->pgmap.ref, priv->num_pages);
+       iov_iter_bvec(&priv->net_tx.iter, WRITE, priv->net_tx.tx_bv,
+                     priv->num_pages, priv->dmabuf->size);
+       return 0;
+}
+
+static void dma_buf_pages_net_tx_free(struct dma_buf_pages *priv)
+{
+       kvfree(priv->net_tx.tx_bv);
+}
+
+const struct dma_buf_pages_type_ops net_tx_ops = {
+       .dma_buf_pages_init             = dma_buf_pages_net_tx_init,
+       .dma_buf_pages_release          = dma_buf_pages_net_tx_release,
+       .dma_buf_pages_destroy          = dma_buf_pages_net_tx_free,
+};
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index e8e66d6407d0..93228a2fec47 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -22,6 +22,7 @@
 #include <linux/fs.h>
 #include <linux/dma-fence.h>
 #include <linux/wait.h>
+#include <linux/uio.h>
 #include <linux/genalloc.h>
 #include <linux/xarray.h>
 #include <net/page_pool.h>
@@ -555,6 +556,11 @@ struct dma_buf_pages_type_ops {
                                  struct page *page);
 };
 
+struct dma_buf_pages_net_tx {
+       struct iov_iter iter;
+       struct bio_vec *tx_bv;
+};
+
 struct dma_buf_pages_net_rx {
        struct gen_pool *page_pool;
        struct xarray bound_rxq_list;
@@ -579,6 +585,7 @@ struct dma_buf_pages {
 
        union {
                struct dma_buf_pages_net_rx net_rx;
+               struct dma_buf_pages_net_tx net_tx;
        };
 };
 
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
index b392cef9d3c6..546f211a7556 100644
--- a/include/uapi/linux/dma-buf.h
+++ b/include/uapi/linux/dma-buf.h
@@ -187,6 +187,7 @@ struct dma_buf_create_pages_info {
 };
 
 #define DMA_BUF_PAGES_NET_RX           (1 << 0)
+#define DMA_BUF_PAGES_NET_TX           (2 << 0)
 
 #define DMA_BUF_CREATE_PAGES   _IOW(DMA_BUF_BASE, 4, struct 
dma_buf_create_pages_info)
 
-- 
2.41.0.390.g38632f3daf-goog