Re: [PATCH] NTB: ntb_transport: Use seq_file for QP stats debugfs

On Tue, Jan 06, 2026 at 09:37:06AM -0700, Dave Jiang wrote:
> 
> 
> On 12/17/25 1:19 AM, Koichiro Den wrote:
> > 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.
> > 
> > While touching this area, fix a bug in the per-QP debugfs directory
> > naming: the buffer used for "qp%d" was only 4 bytes, which truncates
> > names like "qp10" to "qp1" and causes multiple queues to share the same
> > directory. Enlarge the buffer and use sizeof() to avoid truncation.
> > 
> > Reviewed-by: Frank Li <[email protected]>
> > Signed-off-by: Koichiro Den <[email protected]>
> 
> Reviewed-by: Dave Jiang <[email protected]>
> 
> Thanks for the improvement!
> 
> Can you please split out the bug fix and add a Fixes tag so it can go to stable kernels? Thanks!

I have split it out and sent v2 here:
https://lore.kernel.org/all/[email protected]/

Thanks for the review,
Koichiro

> 
> > ---
> > Note: This patch is split out from the following series, where it was
> > originally included as a preparatory change (refactor + small fix):
> > https://lore.kernel.org/all/aS3xe0CNHeIMUu7P@lizhi-Precision-Tower-5810/
> > ---
> >  drivers/ntb/ntb_transport.c | 136 +++++++++++-------------------------
> >  1 file changed, 41 insertions(+), 95 deletions(-)
> > 
> > diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> > index eb875e3db2e3..d5a544bf8fd6 100644
> > --- a/drivers/ntb/ntb_transport.c
> > +++ b/drivers/ntb/ntb_transport.c
> > @@ -57,6 +57,7 @@
> >  #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>
> > @@ -466,104 +467,49 @@ 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)
> > @@ -1236,15 +1182,15 @@ static int ntb_transport_init_queue(struct ntb_transport_ctx *nt,
> >  	qp->tx_max_entry = tx_size / qp->tx_max_frame;
> >  
> >  	if (nt->debugfs_node_dir) {
> > -		char debugfs_name[4];
> > +		char debugfs_name[8];
> >  
> > -		snprintf(debugfs_name, 4, "qp%d", qp_num);
> > +		snprintf(debugfs_name, sizeof(debugfs_name), "qp%d", qp_num);
> >  		qp->debugfs_dir = debugfs_create_dir(debugfs_name,
> >  						     nt->debugfs_node_dir);
> >  
> >  		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;
>