target/rd: fix or rewrite the copy routine

So the code assumes that the sg list is only a array while in reality
loopback SGL memory via scsi_cmnd into target-core may be already
chained.  This patch converts ramdisk code to use sg_miter logic from
scatterlist.h in order to properly support passthrough SGL usage with
transport_generic_map_mem_to_cmd() via loopback.

With this patch the bug goes away. However after umount/mount of the
device my files are gone. So something is still not right. After looking
at it for a while I decided to rewrite the that part of the code and now
things do work for me.

For reference:
- http://article.gmane.org/gmane.linux.scsi.target.devel/595
  the sg_next() conversion
- http://article.gmane.org/gmane.linux.scsi.target.devel/602
  the rewrite of the copy code

(nab: Fix compile warning in rd_MEMCPY)

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable@kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 40 insertions, 205 deletions

diff --git a/drivers/target/target_core_rd.c b/drivers/target/target_core_rd.c
index 6119ed5a3311..02e51faa2f4e 100644
--- a/drivers/target/target_core_rd.c
+++ b/drivers/target/target_core_rd.c
@@ -343,235 +343,74 @@ static struct rd_dev_sg_table *rd_get_sg_table(struct rd_dev *rd_dev, u32 page)
         return NULL;
 }
 
-/*      rd_MEMCPY_read():
- *
- *
- */
-static int rd_MEMCPY_read(struct rd_request *req)
+static int rd_MEMCPY(struct rd_request *req, u32 read_rd)
 {
         struct se_task *task = &req->rd_task;
         struct rd_dev *dev = req->rd_task.task_se_cmd->se_dev->dev_ptr;
         struct rd_dev_sg_table *table;
-        struct scatterlist *sg_d, *sg_s;
-        void *dst, *src;
-        u32 i = 0, j = 0, dst_offset = 0, src_offset = 0;
-        u32 length, page_end = 0, table_sg_end;
+        struct scatterlist *rd_sg;
+        struct sg_mapping_iter m;
         u32 rd_offset = req->rd_offset;
+        u32 src_len;
 
         table = rd_get_sg_table(dev, req->rd_page);
         if (!table)
                 return -EINVAL;
 
-        table_sg_end = (table->page_end_offset - req->rd_page);
-        sg_d = task->task_sg;
-        sg_s = &table->sg_table[req->rd_page - table->page_start_offset];
+        rd_sg = &table->sg_table[req->rd_page - table->page_start_offset];
 
-        pr_debug("RD[%u]: Read LBA: %llu, Size: %u Page: %u, Offset:"
-                " %u\n", dev->rd_dev_id, task->task_lba, req->rd_size,
-                req->rd_page, req->rd_offset);
-
-        src_offset = rd_offset;
+        pr_debug("RD[%u]: %s LBA: %llu, Size: %u Page: %u, Offset: %u\n",
+                        dev->rd_dev_id, read_rd ? "Read" : "Write",
+                        task->task_lba, req->rd_size, req->rd_page,
+                        rd_offset);
 
+        src_len = PAGE_SIZE - rd_offset;
+        sg_miter_start(&m, task->task_sg, task->task_sg_nents,
+                        read_rd ? SG_MITER_TO_SG : SG_MITER_FROM_SG);
         while (req->rd_size) {
-                if ((sg_d[i].length - dst_offset) <
-                    (sg_s[j].length - src_offset)) {
-                        length = (sg_d[i].length - dst_offset);
-
-                        pr_debug("Step 1 - sg_d[%d]: %p length: %d"
-                                " offset: %u sg_s[%d].length: %u\n", i,
-                                &sg_d[i], sg_d[i].length, sg_d[i].offset, j,
-                                sg_s[j].length);
-                        pr_debug("Step 1 - length: %u dst_offset: %u"
-                                " src_offset: %u\n", length, dst_offset,
-                                src_offset);
-
-                        if (length > req->rd_size)
-                                length = req->rd_size;
-
-                        dst = sg_virt(&sg_d[i++]) + dst_offset;
-                        BUG_ON(!dst);
-
-                        src = sg_virt(&sg_s[j]) + src_offset;
-                        BUG_ON(!src);
-
-                        dst_offset = 0;
-                        src_offset = length;
-                        page_end = 0;
-                } else {
-                        length = (sg_s[j].length - src_offset);
-
-                        pr_debug("Step 2 - sg_d[%d]: %p length: %d"
-                                " offset: %u sg_s[%d].length: %u\n", i,
-                                &sg_d[i], sg_d[i].length, sg_d[i].offset,
-                                j, sg_s[j].length);
-                        pr_debug("Step 2 - length: %u dst_offset: %u"
-                                " src_offset: %u\n", length, dst_offset,
-                                src_offset);
-
-                        if (length > req->rd_size)
-                                length = req->rd_size;
-
-                        dst = sg_virt(&sg_d[i]) + dst_offset;
-                        BUG_ON(!dst);
-
-                        if (sg_d[i].length == length) {
-                                i++;
-                                dst_offset = 0;
-                        } else
-                                dst_offset = length;
-
-                        src = sg_virt(&sg_s[j++]) + src_offset;
-                        BUG_ON(!src);
-
-                        src_offset = 0;
-                        page_end = 1;
-                }
+                u32 len;
+                void *rd_addr;
 
-                memcpy(dst, src, length);
+                sg_miter_next(&m);
+                len = min((u32)m.length, src_len);
+                m.consumed = len;
 
-                pr_debug("page: %u, remaining size: %u, length: %u,"
-                        " i: %u, j: %u\n", req->rd_page,
-                        (req->rd_size - length), length, i, j);
+                rd_addr = sg_virt(rd_sg) + rd_offset;
 
-                req->rd_size -= length;
-                if (!req->rd_size)
-                        return 0;
+                if (read_rd)
+                        memcpy(m.addr, rd_addr, len);
+                else
+                        memcpy(rd_addr, m.addr, len);
 
-                if (!page_end)
+                req->rd_size -= len;
+                if (!req->rd_size)
                         continue;
 
-                if (++req->rd_page <= table->page_end_offset) {
-                        pr_debug("page: %u in same page table\n",
-                                req->rd_page);
+                src_len -= len;
+                if (src_len) {
+                        rd_offset += len;
                         continue;
                 }
 
-                pr_debug("getting new page table for page: %u\n",
-                                req->rd_page);
-
-                table = rd_get_sg_table(dev, req->rd_page);
-                if (!table)
-                        return -EINVAL;
-
-                sg_s = &table->sg_table[j = 0];
-        }
-
-        return 0;
-}
-
-/*      rd_MEMCPY_write():
- *
- *
- */
-static int rd_MEMCPY_write(struct rd_request *req)
-{
-        struct se_task *task = &req->rd_task;
-        struct rd_dev *dev = req->rd_task.task_se_cmd->se_dev->dev_ptr;
-        struct rd_dev_sg_table *table;
-        struct scatterlist *sg_d, *sg_s;
-        void *dst, *src;
-        u32 i = 0, j = 0, dst_offset = 0, src_offset = 0;
-        u32 length, page_end = 0, table_sg_end;
-        u32 rd_offset = req->rd_offset;
-
-        table = rd_get_sg_table(dev, req->rd_page);
-        if (!table)
-                return -EINVAL;
-
-        table_sg_end = (table->page_end_offset - req->rd_page);
-        sg_d = &table->sg_table[req->rd_page - table->page_start_offset];
-        sg_s = task->task_sg;
-
-        pr_debug("RD[%d] Write LBA: %llu, Size: %u, Page: %u,"
-                " Offset: %u\n", dev->rd_dev_id, task->task_lba, req->rd_size,
-                req->rd_page, req->rd_offset);
-
-        dst_offset = rd_offset;
-
-        while (req->rd_size) {
-                if ((sg_s[i].length - src_offset) <
-                    (sg_d[j].length - dst_offset)) {
-                        length = (sg_s[i].length - src_offset);
-
-                        pr_debug("Step 1 - sg_s[%d]: %p length: %d"
-                                " offset: %d sg_d[%d].length: %u\n", i,
-                                &sg_s[i], sg_s[i].length, sg_s[i].offset,
-                                j, sg_d[j].length);
-                        pr_debug("Step 1 - length: %u src_offset: %u"
-                                " dst_offset: %u\n", length, src_offset,
-                                dst_offset);
-
-                        if (length > req->rd_size)
-                                length = req->rd_size;
-
-                        src = sg_virt(&sg_s[i++]) + src_offset;
-                        BUG_ON(!src);
-
-                        dst = sg_virt(&sg_d[j]) + dst_offset;
-                        BUG_ON(!dst);
-
-                        src_offset = 0;
-                        dst_offset = length;
-                        page_end = 0;
-                } else {
-                        length = (sg_d[j].length - dst_offset);
-
-                        pr_debug("Step 2 - sg_s[%d]: %p length: %d"
-                                " offset: %d sg_d[%d].length: %u\n", i,
-                                &sg_s[i], sg_s[i].length, sg_s[i].offset,
-                                j, sg_d[j].length);
-                        pr_debug("Step 2 - length: %u src_offset: %u"
-                                " dst_offset: %u\n", length, src_offset,
-                                dst_offset);
-
-                        if (length > req->rd_size)
-                                length = req->rd_size;
-
-                        src = sg_virt(&sg_s[i]) + src_offset;
-                        BUG_ON(!src);
-
-                        if (sg_s[i].length == length) {
-                                i++;
-                                src_offset = 0;
-                        } else
-                                src_offset = length;
-
-                        dst = sg_virt(&sg_d[j++]) + dst_offset;
-                        BUG_ON(!dst);
-
-                        dst_offset = 0;
-                        page_end = 1;
-                }
-
-                memcpy(dst, src, length);
-
-                pr_debug("page: %u, remaining size: %u, length: %u,"
-                        " i: %u, j: %u\n", req->rd_page,
-                        (req->rd_size - length), length, i, j);
-
-                req->rd_size -= length;
-                if (!req->rd_size)
-                        return 0;
-
-                if (!page_end)
-                        continue;
-
-                if (++req->rd_page <= table->page_end_offset) {
-                        pr_debug("page: %u in same page table\n",
-                                req->rd_page);
+                /* rd page completed, next one please */
+                req->rd_page++;
+                rd_offset = 0;
+                src_len = PAGE_SIZE;
+                if (req->rd_page <= table->page_end_offset) {
+                        rd_sg++;
                         continue;
                 }
 
-                pr_debug("getting new page table for page: %u\n",
-                                req->rd_page);
-
                 table = rd_get_sg_table(dev, req->rd_page);
-                if (!table)
+                if (!table) {
+                        sg_miter_stop(&m);
                         return -EINVAL;
+                }
 
-                sg_d = &table->sg_table[j = 0];
+                /* since we increment, the first sg entry is correct */
+                rd_sg = table->sg_table;
         }
-
+        sg_miter_stop(&m);
         return 0;
 }
 
@@ -591,11 +430,7 @@ static int rd_MEMCPY_do_task(struct se_task *task)
         req->rd_page = tmp;
         req->rd_size = task->task_size;
 
-        if (task->task_data_direction == DMA_FROM_DEVICE)
-                ret = rd_MEMCPY_read(req);
-        else
-                ret = rd_MEMCPY_write(req);
-
+        ret = rd_MEMCPY(req, task->task_data_direction == DMA_FROM_DEVICE);
         if (ret != 0)
                 return ret;