1 files changed, 264 insertions, 0 deletions
diff --git a/module/os/linux/spl/spl-procfs-list.c b/module/os/linux/spl/spl-procfs-list.c
new file mode 100644
index 0000000000000..189d6a7c60827
--- /dev/null
+++ b/module/os/linux/spl/spl-procfs-list.c
@@ -0,0 +1,264 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (c) 2018 by Delphix. All rights reserved.
+ */
+
+#include <sys/list.h>
+#include <sys/mutex.h>
+#include <sys/procfs_list.h>
+#include <linux/proc_fs.h>
+
+/*
+ * A procfs_list is a wrapper around a linked list which implements the seq_file
+ * interface, allowing the contents of the list to be exposed through procfs.
+ * The kernel already has some utilities to help implement the seq_file
+ * interface for linked lists (seq_list_*), but they aren't appropriate for use
+ * with lists that have many entries, because seq_list_start walks the list at
+ * the start of each read syscall to find where it left off, so reading a file
+ * ends up being quadratic in the number of entries in the list.
+ *
+ * This implementation avoids this penalty by maintaining a separate cursor into
+ * the list per instance of the file that is open. It also maintains some extra
+ * information in each node of the list to prevent reads of entries that have
+ * been dropped from the list.
+ *
+ * Callers should only add elements to the list using procfs_list_add, which
+ * adds an element to the tail of the list. Other operations can be performed
+ * directly on the wrapped list using the normal list manipulation functions,
+ * but elements should only be removed from the head of the list.
+ */
+
+#define	NODE_ID(procfs_list, obj) \
+		(((procfs_list_node_t *)(((char *)obj) + \
+		(procfs_list)->pl_node_offset))->pln_id)
+
+typedef struct procfs_list_cursor {
+	procfs_list_t	*procfs_list;	/* List into which this cursor points */
+	void		*cached_node;	/* Most recently accessed node */
+	loff_t		cached_pos;	/* Position of cached_node */
+} procfs_list_cursor_t;
+
+static int
+procfs_list_seq_show(struct seq_file *f, void *p)
+{
+	procfs_list_cursor_t *cursor = f->private;
+	procfs_list_t *procfs_list = cursor->procfs_list;
+
+	ASSERT(MUTEX_HELD(&procfs_list->pl_lock));
+	if (p == SEQ_START_TOKEN) {
+		if (procfs_list->pl_show_header != NULL)
+			return (procfs_list->pl_show_header(f));
+		else
+			return (0);
+	}
+	return (procfs_list->pl_show(f, p));
+}
+
+static void *
+procfs_list_next_node(procfs_list_cursor_t *cursor, loff_t *pos)
+{
+	void *next_node;
+	procfs_list_t *procfs_list = cursor->procfs_list;
+
+	if (cursor->cached_node == SEQ_START_TOKEN)
+		next_node = list_head(&procfs_list->pl_list);
+	else
+		next_node = list_next(&procfs_list->pl_list,
+		    cursor->cached_node);
+
+	if (next_node != NULL) {
+		cursor->cached_node = next_node;
+		cursor->cached_pos = NODE_ID(procfs_list, cursor->cached_node);
+		*pos = cursor->cached_pos;
+	}
+	return (next_node);
+}
+
+static void *
+procfs_list_seq_start(struct seq_file *f, loff_t *pos)
+{
+	procfs_list_cursor_t *cursor = f->private;
+	procfs_list_t *procfs_list = cursor->procfs_list;
+
+	mutex_enter(&procfs_list->pl_lock);
+
+	if (*pos == 0) {
+		cursor->cached_node = SEQ_START_TOKEN;
+		cursor->cached_pos = 0;
+		return (SEQ_START_TOKEN);
+	}
+
+	/*
+	 * Check if our cached pointer has become stale, which happens if the
+	 * the message where we left off has been dropped from the list since
+	 * the last read syscall completed.
+	 */
+	void *oldest_node = list_head(&procfs_list->pl_list);
+	if (cursor->cached_node != SEQ_START_TOKEN && (oldest_node == NULL ||
+	    NODE_ID(procfs_list, oldest_node) > cursor->cached_pos))
+		return (ERR_PTR(-EIO));
+
+	/*
+	 * If it isn't starting from the beginning of the file, the seq_file
+	 * code will either pick up at the same position it visited last or the
+	 * following one.
+	 */
+	if (*pos == cursor->cached_pos) {
+		return (cursor->cached_node);
+	} else {
+		ASSERT3U(*pos, ==, cursor->cached_pos + 1);
+		return (procfs_list_next_node(cursor, pos));
+	}
+}
+
+static void *
+procfs_list_seq_next(struct seq_file *f, void *p, loff_t *pos)
+{
+	procfs_list_cursor_t *cursor = f->private;
+	ASSERT(MUTEX_HELD(&cursor->procfs_list->pl_lock));
+	return (procfs_list_next_node(cursor, pos));
+}
+
+static void
+procfs_list_seq_stop(struct seq_file *f, void *p)
+{
+	procfs_list_cursor_t *cursor = f->private;
+	procfs_list_t *procfs_list = cursor->procfs_list;
+	mutex_exit(&procfs_list->pl_lock);
+}
+
+static struct seq_operations procfs_list_seq_ops = {
+	.show  = procfs_list_seq_show,
+	.start = procfs_list_seq_start,
+	.next  = procfs_list_seq_next,
+	.stop  = procfs_list_seq_stop,
+};
+
+static int
+procfs_list_open(struct inode *inode, struct file *filp)
+{
+	int rc = seq_open_private(filp, &procfs_list_seq_ops,
+	    sizeof (procfs_list_cursor_t));
+	if (rc != 0)
+		return (rc);
+
+	struct seq_file *f = filp->private_data;
+	procfs_list_cursor_t *cursor = f->private;
+	cursor->procfs_list = PDE_DATA(inode);
+	cursor->cached_node = NULL;
+	cursor->cached_pos = 0;
+
+	return (0);
+}
+
+static ssize_t
+procfs_list_write(struct file *filp, const char __user *buf, size_t len,
+    loff_t *ppos)
+{
+	struct seq_file *f = filp->private_data;
+	procfs_list_cursor_t *cursor = f->private;
+	procfs_list_t *procfs_list = cursor->procfs_list;
+	int rc;
+
+	if (procfs_list->pl_clear != NULL &&
+	    (rc = procfs_list->pl_clear(procfs_list)) != 0)
+		return (-rc);
+	return (len);
+}
+
+static const kstat_proc_op_t procfs_list_operations = {
+#ifdef HAVE_PROC_OPS_STRUCT
+	.proc_open	= procfs_list_open,
+	.proc_write	= procfs_list_write,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= seq_release_private,
+#else
+	.open		= procfs_list_open,
+	.write		= procfs_list_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release_private,
+#endif
+};
+
+/*
+ * Initialize a procfs_list and create a file for it in the proc filesystem
+ * under the kstat namespace.
+ */
+void
+procfs_list_install(const char *module,
+    const char *name,
+    mode_t mode,
+    procfs_list_t *procfs_list,
+    int (*show)(struct seq_file *f, void *p),
+    int (*show_header)(struct seq_file *f),
+    int (*clear)(procfs_list_t *procfs_list),
+    size_t procfs_list_node_off)
+{
+	mutex_init(&procfs_list->pl_lock, NULL, MUTEX_DEFAULT, NULL);
+	list_create(&procfs_list->pl_list,
+	    procfs_list_node_off + sizeof (procfs_list_node_t),
+	    procfs_list_node_off + offsetof(procfs_list_node_t, pln_link));
+	procfs_list->pl_next_id = 1; /* Save id 0 for SEQ_START_TOKEN */
+	procfs_list->pl_show = show;
+	procfs_list->pl_show_header = show_header;
+	procfs_list->pl_clear = clear;
+	procfs_list->pl_node_offset = procfs_list_node_off;
+
+	kstat_proc_entry_init(&procfs_list->pl_kstat_entry, module, name);
+	kstat_proc_entry_install(&procfs_list->pl_kstat_entry, mode,
+	    &procfs_list_operations, procfs_list);
+}
+EXPORT_SYMBOL(procfs_list_install);
+
+/* Remove the proc filesystem file corresponding to the given list */
+void
+procfs_list_uninstall(procfs_list_t *procfs_list)
+{
+	kstat_proc_entry_delete(&procfs_list->pl_kstat_entry);
+}
+EXPORT_SYMBOL(procfs_list_uninstall);
+
+void
+procfs_list_destroy(procfs_list_t *procfs_list)
+{
+	ASSERT(list_is_empty(&procfs_list->pl_list));
+	list_destroy(&procfs_list->pl_list);
+	mutex_destroy(&procfs_list->pl_lock);
+}
+EXPORT_SYMBOL(procfs_list_destroy);
+
+/*
+ * Add a new node to the tail of the list. While the standard list manipulation
+ * functions can be use for all other operation, adding elements to the list
+ * should only be done using this helper so that the id of the new node is set
+ * correctly.
+ */
+void
+procfs_list_add(procfs_list_t *procfs_list, void *p)
+{
+	ASSERT(MUTEX_HELD(&procfs_list->pl_lock));
+	NODE_ID(procfs_list, p) = procfs_list->pl_next_id++;
+	list_insert_tail(&procfs_list->pl_list, p);
+}
+EXPORT_SYMBOL(procfs_list_add);