linux-kernel - [PATCH v2] dma-debug: add dumping facility via debugfs

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Message-Id: <1547819058-3552-1-git-send-email-clabbe@baylibre.com>
Date:   Fri, 18 Jan 2019 13:44:18 +0000
From:   Corentin Labbe <clabbe@...libre.com>
To:     corbet@....net, hch@....de, m.szyprowski@...sung.com,
        robin.murphy@....com
Cc:     iommu@...ts.linux-foundation.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Corentin Labbe <clabbe@...libre.com>
Subject: [PATCH v2] dma-debug: add dumping facility via debugfs

While debugging a DMA mapping leak, I needed to access
debug_dma_dump_mappings() but easily from user space.

This patch adds a /sys/kernel/debug/dma-api/dump file which contain all
current DMA mapping.

Signed-off-by: Corentin Labbe <clabbe@...libre.com>
---
Changes since v1:
- Use DEFINE_SHOW_ATTRIBUTE
- Add Documentation

 Documentation/DMA-API.txt |  3 +++
 kernel/dma/debug.c        | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index e133ccd60228..78114ee63057 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -696,6 +696,9 @@ dma-api/disabled		This read-only file contains the character 'Y'
 				happen when it runs out of memory or if it was
 				disabled at boot time
 
+dma-api/dump			This read-only file contains current DMA
+				mappings.
+
 dma-api/error_count		This file is read-only and shows the total
 				numbers of errors found.
 
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 23cf5361bcf1..b4827b1c9070 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -144,6 +144,7 @@ static struct dentry *num_free_entries_dent __read_mostly;
 static struct dentry *min_free_entries_dent __read_mostly;
 static struct dentry *nr_total_entries_dent __read_mostly;
 static struct dentry *filter_dent           __read_mostly;
+static struct dentry *dump_dent             __read_mostly;
 
 /* per-driver filter related state */
 
@@ -840,6 +841,36 @@ static const struct file_operations filter_fops = {
 	.llseek = default_llseek,
 };
 
+static int dump_show(struct seq_file *seq, void *v)
+{
+	int idx;
+
+	for (idx = 0; idx < HASH_SIZE; idx++) {
+		struct hash_bucket *bucket = &dma_entry_hash[idx];
+		struct dma_debug_entry *entry;
+		unsigned long flags;
+
+		spin_lock_irqsave(&bucket->lock, flags);
+
+		list_for_each_entry(entry, &bucket->list, list) {
+			seq_printf(seq,
+				   "%s %s %s idx %d P=%llx N=%lx D=%llx L=%llx %s %s\n",
+				   dev_name(entry->dev),
+				   dev_driver_string(entry->dev),
+				   type2name[entry->type], idx,
+				   phys_addr(entry), entry->pfn,
+				   entry->dev_addr, entry->size,
+				   dir2name[entry->direction],
+				   maperr2str[entry->map_err_type]);
+		}
+
+		spin_unlock_irqrestore(&bucket->lock, flags);
+	}
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(dump);
+
 static int dma_debug_fs_init(void)
 {
 	dma_debug_dent = debugfs_create_dir("dma-api", NULL);
@@ -894,6 +925,11 @@ static int dma_debug_fs_init(void)
 	if (!filter_dent)
 		goto out_err;
 
+	dump_dent = debugfs_create_file("dump", 0444,
+					dma_debug_dent, NULL, &dump_fops);
+	if (!dump_dent)
+		goto out_err;
+
 	return 0;
 
 out_err:
-- 
2.19.2