[PATCH v4 3/4] udmabuf: Implement udmabuf direct I/O

[wangtao]

Construct bio_vec from folios, then call the other file's
r/w callbacks for IO operations.
Test data shows direct I/O copy_file_range improves performance by
over 50% vs direct I/O mmap&read (2557 vs 1534).

Test data:
|    32x32MB Read 1024MB  |Creat-ms|Close-ms|  I/O-ms|I/O-MB/s| I/O%
|-------------------------|--------|--------|--------|--------|-----
| 1)Beg udmabuf buffer R/W|    580 |    323 |   1238 |    867 | 100%
| 2)     dmabuf buffer R/W|     48 |      5 |   1149 |    934 | 107%
| 3) udma+memfd buffer R/W|    597 |    340 |   2157 |    497 |  57%
| 4) udma+memfd direct R/W|    573 |    340 |    700 |   1534 | 176%
| 5) u+mfd buffer sendfile|    577 |    340 |   1204 |    891 | 102%
| 6) u+mfd direct sendfile|    567 |    339 |   2272 |    472 |  54%
| 7)   u+mfd buffer splice|    570 |    337 |   1114 |    964 | 111%
| 8)   u+mfd direct splice|    564 |    335 |    793 |   1355 | 156%
| 9)  udmabuf buffer c_f_r|    577 |    323 |   1059 |   1014 | 116%
|10)  udmabuf direct c_f_r|    582 |    325 |    420 |   2557 | 294%
|11)End udmabuf buffer R/W|    586 |    323 |   1188 |    903 | 104%

Signed-off-by: wangtao <tao.wangtao at honor.com>
---
 drivers/dma-buf/udmabuf.c | 54 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index e74e36a8ecda..511567b15340 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -15,6 +15,8 @@
 #include <linux/udmabuf.h>
 #include <linux/vmalloc.h>
 #include <linux/iosys-map.h>
+#include <linux/bvec.h>
+#include <linux/uio.h>
 
 static int list_limit = 1024;
 module_param(list_limit, int, 0644);
@@ -284,6 +286,55 @@ static int end_cpu_udmabuf(struct dma_buf *buf,
 	return 0;
 }
 
+static ssize_t udmabuf_rw_file(struct dma_buf *dmabuf, loff_t my_pos,
+			struct file *other, loff_t pos,
+			size_t count, bool is_write)
+{
+	struct udmabuf *ubuf = dmabuf->priv;
+	loff_t my_end = my_pos + count, bv_beg, bv_end = 0;
+	size_t i, bv_off, bv_len, bv_idx = 0;
+	struct bio_vec *bvec;
+	struct kiocb kiocb;
+	struct iov_iter iter;
+	unsigned int direction = is_write ? ITER_SOURCE : ITER_DEST;
+	ssize_t ret = 0;
+	struct folio *folio;
+
+	bvec = kvcalloc(ubuf->nr_pinned, sizeof(*bvec), GFP_KERNEL);
+	if (!bvec)
+		return -ENOMEM;
+
+	init_sync_kiocb(&kiocb, other);
+	kiocb.ki_pos = pos;
+
+	for (i = 0; i < ubuf->nr_pinned; i++) {
+		folio = ubuf->pinned_folios[i];
+		bv_beg = bv_end;
+		if (bv_beg >= my_end)
+			break;
+		bv_end += folio_size(folio);
+		if (bv_end <= my_pos)
+			continue;
+
+		bv_len = min(bv_end, my_end) - max(my_pos, bv_beg);
+		bv_off = my_pos > bv_beg ? my_pos - bv_beg : 0;
+		bvec_set_page(&bvec[bv_idx], &folio->page, bv_len, bv_off);
+		++bv_idx;
+	}
+
+	if (bv_idx > 0) {
+		/* start R/W. */
+		iov_iter_bvec(&iter, direction, bvec, bv_idx, count);
+		if (is_write)
+			ret = other->f_op->write_iter(&kiocb, &iter);
+		else
+			ret = other->f_op->read_iter(&kiocb, &iter);
+	}
+	kvfree(bvec);
+
+	return ret;
+}
+
 static const struct dma_buf_ops udmabuf_ops = {
 	.cache_sgt_mapping = true,
 	.map_dma_buf	   = map_udmabuf,
@@ -294,6 +345,7 @@ static const struct dma_buf_ops udmabuf_ops = {
 	.vunmap		   = vunmap_udmabuf,
 	.begin_cpu_access  = begin_cpu_udmabuf,
 	.end_cpu_access    = end_cpu_udmabuf,
+	.rw_file = udmabuf_rw_file,
 };
 
 #define SEALS_WANTED (F_SEAL_SHRINK)
@@ -455,6 +507,8 @@ static long udmabuf_create(struct miscdevice *device,
 		ret = PTR_ERR(dmabuf);
 		goto err;
 	}
+	/* Support direct I/O */
+	dmabuf->file->f_mode |= FMODE_CAN_ODIRECT;
 	/*
 	 * Ownership of ubuf is held by the dmabuf from here.
 	 * If the following dma_buf_fd() fails, dma_buf_put() cleans up both the
-- 
2.17.1