zfs-builds-mm/zfs-0.8.1/module/spl/spl-procfs-list.c

258 lines
7.8 KiB
C
Raw Normal View History

2019-07-06 23:40:11 +02:00
/*
* 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 struct file_operations procfs_list_operations = {
.owner = THIS_MODULE,
.open = procfs_list_open,
.write = procfs_list_write,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release_private,
};
/*
* 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);