mm: reuse DEFINE_SHOW_ATTRIBUTE() macro

...instead of open coding file operations followed by custom ->open()
callbacks per each attribute.

[andriy.shevchenko@linux.intel.com: add tags, fix compilation issue]
  Link: http://lkml.kernel.org/r/20180217144253.58604-1-andriy.shevchenko@linux.intel.com
Link: http://lkml.kernel.org/r/20180214154644.54505-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Dennis Zhou <dennisszhou@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/backing-dev.c

@@ -100,18 +100,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
 
 	return 0;
 }
-
-static int bdi_debug_stats_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, bdi_debug_stats_show, inode->i_private);
-}
-
-static const struct file_operations bdi_debug_stats_fops = {
-	.open		= bdi_debug_stats_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);
 
 static int bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 {

mm/memblock.c

@@ -1795,18 +1795,7 @@ static int memblock_debug_show(struct seq_file *m, void *private)
 	}
 	return 0;
 }
-
-static int memblock_debug_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, memblock_debug_show, inode->i_private);
-}
-
-static const struct file_operations memblock_debug_fops = {
-	.open = memblock_debug_open,
-	.read = seq_read,
-	.llseek = seq_lseek,
-	.release = single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(memblock_debug);
 
 static int __init memblock_init_debugfs(void)
 {

mm/percpu-stats.c

@@ -223,18 +223,7 @@ alloc_buffer:
 
 	return 0;
 }
-
-static int percpu_stats_open(struct inode *inode, struct file *filp)
-{
-	return single_open(filp, percpu_stats_show, NULL);
-}
-
-static const struct file_operations percpu_stats_fops = {
-	.open		= percpu_stats_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(percpu_stats);
 
 static int __init init_percpu_stats_debugfs(void)
 {

mm/zsmalloc.c

@@ -642,18 +642,7 @@ static int zs_stats_size_show(struct seq_file *s, void *v)
 
 	return 0;
 }
-
-static int zs_stats_size_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, zs_stats_size_show, inode->i_private);
-}
-
-static const struct file_operations zs_stat_size_ops = {
-	.open           = zs_stats_size_open,
-	.read           = seq_read,
-	.llseek         = seq_lseek,
-	.release        = single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(zs_stats_size);
 
 static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
 {
@@ -672,7 +661,7 @@ static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
 	pool->stat_dentry = entry;
 
 	entry = debugfs_create_file("classes", S_IFREG | S_IRUGO,
-			pool->stat_dentry, pool, &zs_stat_size_ops);
+			pool->stat_dentry, pool, &zs_stats_size_fops);
 	if (!entry) {
 		pr_warn("%s: debugfs file entry <%s> creation failed\n",
 				name, "classes");