diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index e79c00671811..dd6c30ebadfa 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -43,6 +43,7 @@ static char *sg_version_date = "20190606";
 #include <linux/cred.h>			/* for sg_check_file_access() */
 #include <linux/proc_fs.h>
 #include <linux/xarray.h>
+#include <linux/debugfs.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_eh.h>
@@ -67,6 +68,10 @@ static char *sg_version_date = "20190606";
 #endif
 #endif
 
+#if IS_ENABLED(CONFIG_SCSI_PROC_FS) || IS_ENABLED(CONFIG_DEBUG_FS)
+#define SG_PROC_OR_DEBUG_FS 1
+#endif
+
 /* SG_MAX_CDB_SIZE should be 260 (spc4r37 section 3.1.30) however the type
  * of sg_io_hdr::cmd_len can only represent 255. All SCSI commands greater
  * than 16 bytes are "variable length" whose length is a multiple of 4, so:
@@ -268,6 +273,8 @@ struct sg_comm_wr_t {  /* arguments to sg_common_write() */
 static void sg_rq_end_io(struct request *rq, blk_status_t status);
 /* Declarations of other static functions used before they are defined */
 static int sg_proc_init(void);
+static void sg_dfs_init(void);
+static void sg_dfs_exit(void);
 static int sg_start_req(struct sg_request *srp, struct sg_comm_wr_t *cwrp,
 			int dxfer_dir);
 static void sg_finish_scsi_blk_rq(struct sg_request *srp);
@@ -2645,22 +2652,6 @@ sg_remove_device(struct device *cl_dev, struct class_interface *cl_intf)
 	kref_put(&sdp->d_ref, sg_device_destroy);
 }
 
-module_param_named(scatter_elem_sz, scatter_elem_sz, int, S_IRUGO | S_IWUSR);
-module_param_named(def_reserved_size, def_reserved_size, int,
-		   S_IRUGO | S_IWUSR);
-module_param_named(allow_dio, sg_allow_dio, int, S_IRUGO | S_IWUSR);
-
-MODULE_AUTHOR("Douglas Gilbert");
-MODULE_DESCRIPTION("SCSI generic (sg) driver");
-MODULE_LICENSE("GPL");
-MODULE_VERSION(SG_VERSION_STR);
-MODULE_ALIAS_CHARDEV_MAJOR(SCSI_GENERIC_MAJOR);
-
-MODULE_PARM_DESC(scatter_elem_sz, "scatter gather element "
-                "size (default: max(SG_SCATTER_SZ, PAGE_SIZE))");
-MODULE_PARM_DESC(def_reserved_size, "size of buffer reserved for each fd");
-MODULE_PARM_DESC(allow_dio, "allow direct I/O (default: 0 (disallow))");
-
 static int __init
 init_sg(void)
 {
@@ -2710,6 +2701,7 @@ init_sg(void)
 	rc = scsi_register_interface(&sg_interface);
 	if (rc == 0) {
 		sg_proc_init();
+		sg_dfs_init();
 		return 0;
 	}
 	class_destroy(sg_sysfs_class);
@@ -2723,17 +2715,10 @@ init_sg(void)
 	return rc;
 }
 
-#if !IS_ENABLED(CONFIG_SCSI_PROC_FS)
-static int
-sg_proc_init(void)
-{
-	return 0;
-}
-#endif
-
 static void __exit
 exit_sg(void)
 {
+	sg_dfs_exit();
 	if (IS_ENABLED(CONFIG_SCSI_PROC_FS))
 		remove_proc_subtree("scsi/sg", NULL);
 	scsi_unregister_interface(&sg_interface);
@@ -3163,7 +3148,7 @@ sg_find_srp_by_id(struct sg_fd *sfp, int pack_id)
 	/* here if one of above loops does _not_ find a match */
 	if (IS_ENABLED(CONFIG_SCSI_PROC_FS)) {
 		if (search_for_1) {
-			const char *cptp = "pack_id=";
+			__maybe_unused const char *cptp = "pack_id=";
 
 			if (is_bad_st)
 				SG_LOG(1, sfp, "%s: %s%d wrong state: %s\n",
@@ -3600,17 +3585,6 @@ sg_remove_sfp(struct kref *kref)
 	schedule_work(&sfp->ew_fd.work);
 }
 
-static int
-sg_idr_max_id(int id, void *p, void *data)
-		__must_hold(sg_index_lock)
-{
-	int *k = data;
-
-	if (*k < id)
-		*k = id;
-	return 0;
-}
-
 /* must be called with sg_index_lock held */
 static struct sg_device *
 sg_lookup_dev(int dev)
@@ -3640,7 +3614,7 @@ sg_get_dev(int dev)
 	return sdp;
 }
 
-#if IS_ENABLED(CONFIG_SCSI_PROC_FS)
+#if IS_ENABLED(SG_PROC_OR_DEBUG_FS)
 static const char *
 sg_rq_st_str(enum sg_rq_state rq_st, bool long_str)
 {
@@ -3669,7 +3643,35 @@ sg_rq_st_str(enum sg_rq_state rq_st, bool long_str)
 }
 #endif
 
-#if IS_ENABLED(CONFIG_SCSI_PROC_FS)     /* long, almost to end of file */
+#if IS_ENABLED(SG_PROC_OR_DEBUG_FS)
+
+#define SG_SNAPSHOT_DEV_MAX 4
+
+/*
+ * For snapshot_devs array, -1 or two adjacent the same is terminator.
+ * -1 in first element of first two elements the same implies all.
+ */
+static struct sg_dfs_context_t {
+	struct dentry *dfs_rootdir;
+	int snapshot_devs[SG_SNAPSHOT_DEV_MAX];
+} sg_dfs_cxt;
+
+struct sg_proc_deviter {
+	loff_t	index;
+	size_t	max;
+	int fd_index;
+};
+
+static int
+sg_idr_max_id(int id, void *p, void *data)
+		__must_hold(sg_index_lock)
+{
+	int *k = data;
+
+	if (*k < id)
+		*k = id;
+	return 0;
+}
 
 static int
 sg_last_dev(void)
@@ -3683,6 +3685,41 @@ sg_last_dev(void)
 	return k + 1;		/* origin 1 */
 }
 
+static void *
+dev_seq_start(struct seq_file *s, loff_t *pos)
+{
+	struct sg_proc_deviter *it = kzalloc(sizeof(*it), GFP_KERNEL);
+
+	s->private = it;
+	if (!it)
+		return NULL;
+
+	it->index = *pos;
+	it->max = sg_last_dev();
+	if (it->index >= it->max)
+		return NULL;
+	return it;
+}
+
+static void *
+dev_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	struct sg_proc_deviter *it = s->private;
+
+	*pos = ++it->index;
+	return (it->index < it->max) ? it : NULL;
+}
+
+static void
+dev_seq_stop(struct seq_file *s, void *v)
+{
+	kfree(s->private);
+}
+
+#endif			/* SG_PROC_OR_DEBUG_FS */
+
+#if IS_ENABLED(CONFIG_SCSI_PROC_FS)     /* around 100 lines */
+
 static int
 sg_proc_seq_show_int(struct seq_file *s, void *v)
 {
@@ -3696,7 +3733,7 @@ sg_proc_single_open_adio(struct inode *inode, struct file *filp)
 	return single_open(filp, sg_proc_seq_show_int, &sg_allow_dio);
 }
 
-static ssize_t 
+static ssize_t
 sg_proc_write_adio(struct file *filp, const char __user *buffer,
 		   size_t count, loff_t *off)
 {
@@ -3718,7 +3755,7 @@ sg_proc_single_open_dressz(struct inode *inode, struct file *filp)
 	return single_open(filp, sg_proc_seq_show_int, &sg_big_buff);
 }
 
-static ssize_t 
+static ssize_t
 sg_proc_write_dressz(struct file *filp, const char __user *buffer,
 		     size_t count, loff_t *off)
 {
@@ -3753,43 +3790,6 @@ sg_proc_seq_show_devhdr(struct seq_file *s, void *v)
 	return 0;
 }
 
-struct sg_proc_deviter {
-	loff_t	index;
-	size_t	max;
-	int fd_index;
-};
-
-static void *
-dev_seq_start(struct seq_file *s, loff_t *pos)
-{
-	struct sg_proc_deviter *it = kzalloc(sizeof(*it), GFP_KERNEL);
-
-	s->private = it;
-	if (! it)
-		return NULL;
-
-	it->index = *pos;
-	it->max = sg_last_dev();
-	if (it->index >= it->max)
-		return NULL;
-	return it;
-}
-
-static void *
-dev_seq_next(struct seq_file *s, void *v, loff_t *pos)
-{
-	struct sg_proc_deviter *it = s->private;
-
-	*pos = ++it->index;
-	return (it->index < it->max) ? it : NULL;
-}
-
-static void
-dev_seq_stop(struct seq_file *s, void *v)
-{
-	kfree(s->private);
-}
-
 static int
 sg_proc_seq_show_dev(struct seq_file *s, void *v)
 {
@@ -3836,6 +3836,10 @@ sg_proc_seq_show_devstrs(struct seq_file *s, void *v)
 	return 0;
 }
 
+#endif		/* CONFIG_SCSI_PROC_FS (~100 lines back) */
+
+#if IS_ENABLED(SG_PROC_OR_DEBUG_FS)
+
 /* Writes debug info for one sg_request in obp buffer */
 static int
 sg_proc_debug_sreq(struct sg_request *srp, int to, char *obp, int len)
@@ -3978,18 +3982,20 @@ sg_proc_seq_show_debug(struct seq_file *s, void *v)
 	bool found = false;
 	bool trunc = false;
 	const int bp_len = SG_PROC_DEBUG_SZ;
+	int j, sd_n;
 	int n = 0;
 	int k = 0;
 	unsigned long iflags;
 	struct sg_proc_deviter *it = (struct sg_proc_deviter *)v;
 	struct sg_device *sdp;
 	int *fdi_p;
+	const int *dev_arr = sg_dfs_cxt.snapshot_devs;
 	char *bp;
 	char *disk_name;
 	char b1[128];
 
 	b1[0] = '\0';
-	if (it && (0 == it->index))
+	if (it && it->index == 0)
 		seq_printf(s, "max_active_device=%d  def_reserved_size=%d\n",
 			   (int)it->max, def_reserved_size);
 	fdi_p = it ? &it->fd_index : &k;
@@ -4001,8 +4007,31 @@ sg_proc_seq_show_debug(struct seq_file *s, void *v)
 	}
 	read_lock_irqsave(&sg_index_lock, iflags);
 	sdp = it ? sg_lookup_dev(it->index) : NULL;
-	if (NULL == sdp)
+	if (!sdp)
 		goto skip;
+	sd_n = dev_arr[0];
+	if (sd_n != -1 && sd_n != sdp->index && sd_n != dev_arr[1]) {
+		for (j = 1; j < SG_SNAPSHOT_DEV_MAX; ) {
+			sd_n = dev_arr[j];
+			if (sd_n < 0)
+				goto skip;
+			++j;
+			if (j >= SG_SNAPSHOT_DEV_MAX) {
+				if (sd_n == sdp->index) {
+					found = true;
+					break;
+				}
+			} else if (sd_n == dev_arr[j]) {
+				goto skip;
+			} else if (sd_n == sdp->index) {
+				found = true;
+				break;
+			}
+		}
+		if (!found)
+			goto skip;
+		found = false;
+	}
 	if (!xa_empty(&sdp->sfp_arr)) {
 		found = true;
 		disk_name = (sdp->name[0] ? sdp->name : "?_?");
@@ -4042,6 +4071,10 @@ sg_proc_seq_show_debug(struct seq_file *s, void *v)
 	return 0;
 }
 
+#endif         /* SG_PROC_OR_DEBUG_FS */
+
+#if IS_ENABLED(CONFIG_SCSI_PROC_FS)
+
 static const struct proc_ops adio_proc_ops = {
 	.proc_open      = sg_proc_single_open_adio,
 	.proc_read      = seq_read,
@@ -4100,7 +4133,226 @@ sg_proc_init(void)
 
 /* remove_proc_subtree("scsi/sg", NULL) in exit_sg() does cleanup */
 
-#endif				/* CONFIG_SCSI_PROC_FS (~400 lines back) */
+#else
+
+static int
+sg_proc_init(void)
+{
+	return 0;
+}
+
+#endif			/* CONFIG_SCSI_PROC_FS */
+
+#if IS_ENABLED(CONFIG_DEBUG_FS)
+
+struct sg_dfs_attr {
+	const char *name;
+	umode_t mode;
+	int (*show)(void *d, struct seq_file *m);
+	ssize_t (*write)(void *d, const char __user *b, size_t s, loff_t *o);
+	/* Set either .show or .seq_ops. */
+	const struct seq_operations *seq_ops;
+};
 
+static int
+sg_dfs_snapshot_devs_show(void *data, struct seq_file *m)
+{
+	bool last;
+	int k, d;
+	struct sg_dfs_context_t *ctxp = data;
+
+	for (k = 0; k < SG_SNAPSHOT_DEV_MAX; ++k) {
+		d = ctxp->snapshot_devs[k];
+		last = (k + 1 == SG_SNAPSHOT_DEV_MAX);
+		if (d < 0) {
+			if (k == 0)
+				seq_puts(m, "-1");
+			break;
+		}
+		if (!last && d == ctxp->snapshot_devs[k + 1]) {
+			if (k == 0)
+				seq_puts(m, "-1");
+			break;
+		}
+		if (k != 0)
+			seq_puts(m, ",");
+		seq_printf(m, "%d", d);
+	}
+	seq_puts(m, "\n");
+	return 0;
+}
+
+static ssize_t
+sg_dfs_snapshot_devs_write(void *data, const char __user *buf, size_t count,
+			   loff_t *ppos)
+{
+	bool trailing_comma;
+	int k, n;
+	struct sg_dfs_context_t *cxtp = data;
+	char lbuf[64] = { }, *cp, *c2p;
+
+	if (count >= sizeof(lbuf)) {
+		pr_err("%s: operation too long\n", __func__);
+		return -EINVAL;
+	}
+	if (copy_from_user(lbuf, buf, count))
+		return -EFAULT;
+	for (k = 0, n = 0, cp = lbuf; k < SG_SNAPSHOT_DEV_MAX;
+	     ++k, cp = c2p + 1) {
+		c2p = strchr(cp, ',');
+		if (c2p)
+			*c2p = '\0';
+		trailing_comma = !!c2p;
+		/* sscanf is easier to use that this ... */
+		if (kstrtoint(cp, 10, cxtp->snapshot_devs + k))
+			break;
+		++n;
+		if (!trailing_comma)
+			break;
+	}
+	if (n == 0) {
+		return -EINVAL;
+	} else if (k >= SG_SNAPSHOT_DEV_MAX && trailing_comma) {
+		pr_err("%s: only %d elements in snapshot array\n", __func__,
+		       SG_SNAPSHOT_DEV_MAX);
+		return -EINVAL;
+	}
+	if (n < SG_SNAPSHOT_DEV_MAX)
+		cxtp->snapshot_devs[n] = -1;
+	return count;
+}
+
+static int
+sg_dfs_show(struct seq_file *m, void *v)
+{
+	const struct sg_dfs_attr *attr = m->private;
+	void *data = d_inode(m->file->f_path.dentry->d_parent)->i_private;
+
+	return attr->show(data, m);
+}
+
+static ssize_t
+sg_dfs_write(struct file *file, const char __user *buf, size_t count,
+	     loff_t *ppos)
+{
+	struct seq_file *m = file->private_data;
+	const struct sg_dfs_attr *attr = m->private;
+	void *data = d_inode(file->f_path.dentry->d_parent)->i_private;
+
+	/*
+	 * Attributes that only implement .seq_ops are read-only and 'attr' is
+	 * the same with 'data' in this case.
+	 */
+	if (attr == data || !attr->write)
+		return -EPERM;
+	return attr->write(data, buf, count, ppos);
+}
+
+static int
+sg_dfs_open(struct inode *inode, struct file *file)
+{
+	const struct sg_dfs_attr *attr = inode->i_private;
+	void *data = d_inode(file->f_path.dentry->d_parent)->i_private;
+	struct seq_file *m;
+	int ret;
+
+	if (attr->seq_ops) {
+		ret = seq_open(file, attr->seq_ops);
+		if (!ret) {
+			m = file->private_data;
+			m->private = data;
+		}
+		return ret;
+	}
+	if (WARN_ON_ONCE(!attr->show))
+		return -EPERM;
+	return single_open(file, sg_dfs_show, inode->i_private);
+}
+
+static int
+sg_dfs_release(struct inode *inode, struct file *file)
+{
+	const struct sg_dfs_attr *attr = inode->i_private;
+
+	if (attr->show)
+		return single_release(inode, file);
+	return seq_release(inode, file);
+}
+
+static const struct file_operations sg_dfs_fops = {
+	.owner		= THIS_MODULE,
+	.open		= sg_dfs_open,
+	.read		= seq_read,
+	.write		= sg_dfs_write,
+	.llseek		= seq_lseek,
+	.release	= sg_dfs_release,
+};
+
+static void sg_dfs_mk_files(struct dentry *parent, void *data,
+			    const struct sg_dfs_attr *attr)
+{
+	if (IS_ERR_OR_NULL(parent))
+		return;
+
+	d_inode(parent)->i_private = data;
+	for (; attr->name; ++attr)
+		debugfs_create_file(attr->name, attr->mode, parent,
+				    (void *)attr, &sg_dfs_fops);
+}
+
+static const struct seq_operations sg_snapshot_seq_ops = {
+	.start = dev_seq_start,
+	.next  = dev_seq_next,
+	.stop  = dev_seq_stop,
+	.show  = sg_proc_seq_show_debug,
+};
+
+static const struct sg_dfs_attr sg_dfs_attrs[] = {
+	{"snapshot", 0400, .seq_ops = &sg_snapshot_seq_ops},
+	{"snapshot_devs", 0600, sg_dfs_snapshot_devs_show,
+	 sg_dfs_snapshot_devs_write},
+	{ },
+};
+
+static void
+sg_dfs_init(void)
+{
+	/* create and populate /sys/kernel/debug/scsi_generic directory */
+	if (!sg_dfs_cxt.dfs_rootdir) {
+		sg_dfs_cxt.dfs_rootdir = debugfs_create_dir("scsi_generic",
+							    NULL);
+		sg_dfs_mk_files(sg_dfs_cxt.dfs_rootdir, &sg_dfs_cxt,
+				sg_dfs_attrs);
+	}
+	sg_dfs_cxt.snapshot_devs[0] = -1;	/* show all sg devices */
+}
+
+static void
+sg_dfs_exit(void)
+{
+	debugfs_remove_recursive(sg_dfs_cxt.dfs_rootdir);
+	sg_dfs_cxt.dfs_rootdir = NULL;
+}
+
+#else		/* not  defined: CONFIG_DEBUG_FS */
+
+static void sg_dfs_init(void) {}
+static void sg_dfs_exit(void) {}
+
+#endif		/* CONFIG_DEBUG_FS */
+
+module_param_named(scatter_elem_sz, scatter_elem_sz, int, 0644);
+module_param_named(def_reserved_size, def_reserved_size, int, 0644);
+module_param_named(allow_dio, sg_allow_dio, int, 0644);
+
+MODULE_AUTHOR("Douglas Gilbert");
+MODULE_DESCRIPTION("SCSI generic (sg) driver");
+MODULE_LICENSE("GPL");
+MODULE_VERSION(SG_VERSION_STR);
+MODULE_ALIAS_CHARDEV_MAJOR(SCSI_GENERIC_MAJOR);
+
+MODULE_PARM_DESC(scatter_elem_sz, "scatter gather element size (default: max(SG_SCATTER_SZ, PAGE_SIZE))");
+MODULE_PARM_DESC(def_reserved_size, "size of buffer reserved for each fd");
+MODULE_PARM_DESC(allow_dio, "allow direct I/O (default: 0 (disallow))");
 module_init(init_sg);
 module_exit(exit_sg);
