NTB: ntb_transport: Use seq_file for QP stats debugfs

The ./qp*/stats debugfs file for each NTB transport QP is currently
implemented with a hand-crafted kmalloc() buffer and a series of
scnprintf() calls. This is a pre-seq_file style pattern and makes future
extensions easy to truncate.

Convert the stats file to use the seq_file helpers via
DEFINE_SHOW_ATTRIBUTE(), which simplifies the code and lets the seq_file
core handle buffering and partial reads.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

Author: Koichiro Den

drivers/ntb/ntb_transport.c

@@ -58,6 +58,7 @@
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/slab.h>
+#include <linux/seq_file.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
 #include <linux/mutex.h>
@@ -482,104 +483,49 @@ void ntb_transport_unregister_client(struct ntb_transport_client *drv)
 }
 EXPORT_SYMBOL_GPL(ntb_transport_unregister_client);
 
-static ssize_t debugfs_read(struct file *filp, char __user *ubuf, size_t count,
-			    loff_t *offp)
+static int ntb_qp_debugfs_stats_show(struct seq_file *s, void *v)
 {
-	struct ntb_transport_qp *qp;
-	char *buf;
-	ssize_t ret, out_offset, out_count;
-
-	qp = filp->private_data;
+	struct ntb_transport_qp *qp = s->private;
 
 	if (!qp || !qp->link_is_up)
 		return 0;
 
-	out_count = 1000;
-
-	buf = kmalloc(out_count, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
+	seq_puts(s, "\nNTB QP stats:\n\n");
+
+	seq_printf(s, "rx_bytes - \t%llu\n", qp->rx_bytes);
+	seq_printf(s, "rx_pkts - \t%llu\n", qp->rx_pkts);
+	seq_printf(s, "rx_memcpy - \t%llu\n", qp->rx_memcpy);
+	seq_printf(s, "rx_async - \t%llu\n", qp->rx_async);
+	seq_printf(s, "rx_ring_empty - %llu\n", qp->rx_ring_empty);
+	seq_printf(s, "rx_err_no_buf - %llu\n", qp->rx_err_no_buf);
+	seq_printf(s, "rx_err_oflow - \t%llu\n", qp->rx_err_oflow);
+	seq_printf(s, "rx_err_ver - \t%llu\n", qp->rx_err_ver);
+	seq_printf(s, "rx_buff - \t0x%p\n", qp->rx_buff);
+	seq_printf(s, "rx_index - \t%u\n", qp->rx_index);
+	seq_printf(s, "rx_max_entry - \t%u\n", qp->rx_max_entry);
+	seq_printf(s, "rx_alloc_entry - \t%u\n\n", qp->rx_alloc_entry);
+
+	seq_printf(s, "tx_bytes - \t%llu\n", qp->tx_bytes);
+	seq_printf(s, "tx_pkts - \t%llu\n", qp->tx_pkts);
+	seq_printf(s, "tx_memcpy - \t%llu\n", qp->tx_memcpy);
+	seq_printf(s, "tx_async - \t%llu\n", qp->tx_async);
+	seq_printf(s, "tx_ring_full - \t%llu\n", qp->tx_ring_full);
+	seq_printf(s, "tx_err_no_buf - %llu\n", qp->tx_err_no_buf);
+	seq_printf(s, "tx_mw - \t0x%p\n", qp->tx_mw);
+	seq_printf(s, "tx_index (H) - \t%u\n", qp->tx_index);
+	seq_printf(s, "RRI (T) - \t%u\n", qp->remote_rx_info->entry);
+	seq_printf(s, "tx_max_entry - \t%u\n", qp->tx_max_entry);
+	seq_printf(s, "free tx - \t%u\n", ntb_transport_tx_free_entry(qp));
+	seq_putc(s, '\n');
+
+	seq_printf(s, "Using TX DMA - \t%s\n", qp->tx_dma_chan ? "Yes" : "No");
+	seq_printf(s, "Using RX DMA - \t%s\n", qp->rx_dma_chan ? "Yes" : "No");
+	seq_printf(s, "QP Link - \t%s\n", qp->link_is_up ? "Up" : "Down");
+	seq_putc(s, '\n');
 
-	out_offset = 0;
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "\nNTB QP stats:\n\n");
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_bytes - \t%llu\n", qp->rx_bytes);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_pkts - \t%llu\n", qp->rx_pkts);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_memcpy - \t%llu\n", qp->rx_memcpy);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_async - \t%llu\n", qp->rx_async);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_ring_empty - %llu\n", qp->rx_ring_empty);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_err_no_buf - %llu\n", qp->rx_err_no_buf);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_err_oflow - \t%llu\n", qp->rx_err_oflow);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_err_ver - \t%llu\n", qp->rx_err_ver);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_buff - \t0x%p\n", qp->rx_buff);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_index - \t%u\n", qp->rx_index);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_max_entry - \t%u\n", qp->rx_max_entry);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "rx_alloc_entry - \t%u\n\n", qp->rx_alloc_entry);
-
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_bytes - \t%llu\n", qp->tx_bytes);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_pkts - \t%llu\n", qp->tx_pkts);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_memcpy - \t%llu\n", qp->tx_memcpy);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_async - \t%llu\n", qp->tx_async);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_ring_full - \t%llu\n", qp->tx_ring_full);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_err_no_buf - %llu\n", qp->tx_err_no_buf);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_mw - \t0x%p\n", qp->tx_mw);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_index (H) - \t%u\n", qp->tx_index);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "RRI (T) - \t%u\n",
-			       qp->remote_rx_info->entry);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "tx_max_entry - \t%u\n", qp->tx_max_entry);
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "free tx - \t%u\n",
-			       ntb_transport_tx_free_entry(qp));
-
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "\n");
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "Using TX DMA - \t%s\n",
-			       qp->tx_dma_chan ? "Yes" : "No");
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "Using RX DMA - \t%s\n",
-			       qp->rx_dma_chan ? "Yes" : "No");
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "QP Link - \t%s\n",
-			       qp->link_is_up ? "Up" : "Down");
-	out_offset += scnprintf(buf + out_offset, out_count - out_offset,
-			       "\n");
-
-	if (out_offset > out_count)
-		out_offset = out_count;
-
-	ret = simple_read_from_buffer(ubuf, count, offp, buf, out_offset);
-	kfree(buf);
-	return ret;
-}
-
-static const struct file_operations ntb_qp_debugfs_stats = {
-	.owner = THIS_MODULE,
-	.open = simple_open,
-	.read = debugfs_read,
-};
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ntb_qp_debugfs_stats);
 
 static void ntb_list_add(spinlock_t *lock, struct list_head *entry,
 			 struct list_head *list)
@@ -1260,7 +1206,7 @@ static int ntb_transport_init_queue(struct ntb_transport_ctx *nt,
 
 		qp->debugfs_stats = debugfs_create_file("stats", S_IRUSR,
 							qp->debugfs_dir, qp,
-							&ntb_qp_debugfs_stats);
+							&ntb_qp_debugfs_stats_fops);
 	} else {
 		qp->debugfs_dir = NULL;
 		qp->debugfs_stats = NULL;