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 <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

Documentation/DMA-API.txt

···
 				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.
 

kernel/dma/debug.c

···
 	.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 void dma_debug_fs_init(void)
 {
 	struct dentry *dentry = debugfs_create_dir("dma-api", NULL);
···
 	debugfs_create_u32("min_free_entries", 0444, dentry, &min_free_entries);
 	debugfs_create_u32("nr_total_entries", 0444, dentry, &nr_total_entries);
 	debugfs_create_file("driver_filter", 0644, dentry, NULL, &filter_fops);
+	debugfs_create_file("dump", 0444, dentry, NULL, &dump_fops);
 }
 
 static int device_dma_allocations(struct device *dev, struct dma_debug_entry **out_entry)