Messages in this thread | | | Date | Tue, 24 Jun 2008 15:20:04 +0200 | From | Louis Rilling <> | Subject | Re: [PATCH 0/2]v2 configfs: symlink() fixes |
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On Mon, Jun 23, 2008 at 03:20:44PM -0700, Joel Becker wrote: > On Mon, Jun 23, 2008 at 02:16:16PM +0200, Louis Rilling wrote: > > The following patchset fixes incorrect symlinks to dead items in configfs, which > > are forbidden by specification. > > > > The first patch actually prevents such dangling symlinks from being created, but > > introduces a weird(?) behavior where a failing symlink() can make a racing > > rmdir() fail in the symlink's parent and in the symlink's target as well. This > > behavior is fixed with the next patch. > > Silly question: you've tested this, right?
Yup. I tested this on Linux 2.6.26-rc5 with a modified example_configfs.c (attached), and on a backport for 2.6.20 with my own subsystem (based on Kerrighed http://www.kerrighed.org/wiki/index.php/SchedConfig ).
Do you have some regression tests?
sample tests for symlinks:
mkdir -p /config/03-group-children/c1/c1.1 cd /config/03-group-children/c1/c1.1
# repeatedly create and remove a symlink to self ln -s . link rm link ln -s . link rm link
mkdir /config/02-simple-children/c2
# repeatedly create and remove a symlink to another item ln -s /config/02-simple-children/c2 link rm link ln -s /config/02-simple-children/c2 link rm link
# create two links with inverted source and target ln -s /config/02-simple-children/c2 link ln -s . /config/02-simple-children/c2/link rm link rm /config/02-simple-children/c2/link
# try hard to create a link to a removed item # last loop is to be run in a separate shell cd /config/03-group-children/c1 while true; do mkdir c1.1 && echo mkdir ok; rmdir c1.1 && echo rmdir ok; done # in a separate shell cd /config/02-simple-children/c2 while true; do ln -s /config/03-group-children/c1/c1.1 link && echo ln ok && \ (ls link/ || (echo failed!!!; read foo)) && rm link; done
Louis
-- Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes /* * vim: noexpandtab ts=8 sts=0 sw=8: * * configfs_example.c - This file is a demonstration module containing * a number of configfs subsystems. * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * General Public License for more details. * * You should have received a copy of the GNU General Public * License along with this program; if not, write to the * Free Software Foundation, Inc., 59 Temple Place - Suite 330, * Boston, MA 021110-1307, USA. * * Based on sysfs: * sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel * * configfs Copyright (C) 2005 Oracle. All rights reserved. */
#include <linux/init.h> #include <linux/module.h> #include <linux/slab.h>
#include <linux/configfs.h>
/* * 01-childless * * This first example is a childless subsystem. It cannot create * any config_items. It just has attributes. * * Note that we are enclosing the configfs_subsystem inside a container. * This is not necessary if a subsystem has no attributes directly * on the subsystem. See the next example, 02-simple-children, for * such a subsystem. */
struct childless { struct configfs_subsystem subsys; int showme; int storeme; };
struct childless_attribute { struct configfs_attribute attr; ssize_t (*show)(struct childless *, char *); ssize_t (*store)(struct childless *, const char *, size_t); };
static inline struct childless *to_childless(struct config_item *item) { return item ? container_of(to_configfs_subsystem(to_config_group(item)), struct childless, subsys) : NULL; }
static ssize_t childless_showme_read(struct childless *childless, char *page) { ssize_t pos;
pos = sprintf(page, "%d\n", childless->showme); childless->showme++;
return pos; }
static ssize_t childless_storeme_read(struct childless *childless, char *page) { return sprintf(page, "%d\n", childless->storeme); }
static ssize_t childless_storeme_write(struct childless *childless, const char *page, size_t count) { unsigned long tmp; char *p = (char *) page;
tmp = simple_strtoul(p, &p, 10); if (!p || (*p && (*p != '\n'))) return -EINVAL;
if (tmp > INT_MAX) return -ERANGE;
childless->storeme = tmp;
return count; }
static ssize_t childless_description_read(struct childless *childless, char *page) { return sprintf(page, "[01-childless]\n" "\n" "The childless subsystem is the simplest possible subsystem in\n" "configfs. It does not support the creation of child config_items.\n" "It only has a few attributes. In fact, it isn't much different\n" "than a directory in /proc.\n"); }
static struct childless_attribute childless_attr_showme = { .attr = { .ca_owner = THIS_MODULE, .ca_name = "showme", .ca_mode = S_IRUGO }, .show = childless_showme_read, }; static struct childless_attribute childless_attr_storeme = { .attr = { .ca_owner = THIS_MODULE, .ca_name = "storeme", .ca_mode = S_IRUGO | S_IWUSR }, .show = childless_storeme_read, .store = childless_storeme_write, }; static struct childless_attribute childless_attr_description = { .attr = { .ca_owner = THIS_MODULE, .ca_name = "description", .ca_mode = S_IRUGO }, .show = childless_description_read, };
static struct configfs_attribute *childless_attrs[] = { &childless_attr_showme.attr, &childless_attr_storeme.attr, &childless_attr_description.attr, NULL, };
static ssize_t childless_attr_show(struct config_item *item, struct configfs_attribute *attr, char *page) { struct childless *childless = to_childless(item); struct childless_attribute *childless_attr = container_of(attr, struct childless_attribute, attr); ssize_t ret = 0;
if (childless_attr->show) ret = childless_attr->show(childless, page); return ret; }
static ssize_t childless_attr_store(struct config_item *item, struct configfs_attribute *attr, const char *page, size_t count) { struct childless *childless = to_childless(item); struct childless_attribute *childless_attr = container_of(attr, struct childless_attribute, attr); ssize_t ret = -EINVAL;
if (childless_attr->store) ret = childless_attr->store(childless, page, count); return ret; }
static struct configfs_item_operations childless_item_ops = { .show_attribute = childless_attr_show, .store_attribute = childless_attr_store, };
static struct config_item_type childless_type = { .ct_item_ops = &childless_item_ops, .ct_attrs = childless_attrs, .ct_owner = THIS_MODULE, };
static struct childless childless_subsys = { .subsys = { .su_group = { .cg_item = { .ci_namebuf = "01-childless", .ci_type = &childless_type, }, }, }, };
/* ----------------------------------------------------------------- */
/* * 02-simple-children * * This example merely has a simple one-attribute child. Note that * there is no extra attribute structure, as the child's attribute is * known from the get-go. Also, there is no container for the * subsystem, as it has no attributes of its own. */
struct simple_child { struct config_item item; int storeme; };
static inline struct simple_child *to_simple_child(struct config_item *item) { return item ? container_of(item, struct simple_child, item) : NULL; }
static struct configfs_attribute simple_child_attr_storeme = { .ca_owner = THIS_MODULE, .ca_name = "storeme", .ca_mode = S_IRUGO | S_IWUSR, };
static struct configfs_attribute *simple_child_attrs[] = { &simple_child_attr_storeme, NULL, };
static ssize_t simple_child_attr_show(struct config_item *item, struct configfs_attribute *attr, char *page) { ssize_t count; struct simple_child *simple_child = to_simple_child(item);
count = sprintf(page, "%d\n", simple_child->storeme);
return count; }
static ssize_t simple_child_attr_store(struct config_item *item, struct configfs_attribute *attr, const char *page, size_t count) { struct simple_child *simple_child = to_simple_child(item); unsigned long tmp; char *p = (char *) page;
tmp = simple_strtoul(p, &p, 10); if (!p || (*p && (*p != '\n'))) return -EINVAL;
if (tmp > INT_MAX) return -ERANGE;
simple_child->storeme = tmp;
return count; }
static void simple_child_release(struct config_item *item) { kfree(to_simple_child(item)); }
/* Forward declaration */ static struct config_item_type simple_child_type;
static int simple_child_allow_link(struct config_item *src, struct config_item *target) { return (target->ci_type == &simple_child_type) ? 0 : -EPERM; }
static struct configfs_item_operations simple_child_item_ops = { .release = simple_child_release, .show_attribute = simple_child_attr_show, .store_attribute = simple_child_attr_store, .allow_link = simple_child_allow_link, };
static struct config_item_type simple_child_type = { .ct_item_ops = &simple_child_item_ops, .ct_attrs = simple_child_attrs, .ct_owner = THIS_MODULE, };
struct simple_children { struct config_group group; };
static inline struct simple_children *to_simple_children(struct config_item *item) { return item ? container_of(to_config_group(item), struct simple_children, group) : NULL; }
static struct config_item *simple_children_make_item(struct config_group *group, const char *name) { struct simple_child *simple_child;
simple_child = kzalloc(sizeof(struct simple_child), GFP_KERNEL); if (!simple_child) return NULL;
config_item_init_type_name(&simple_child->item, name, &simple_child_type);
simple_child->storeme = 0;
return &simple_child->item; }
static struct configfs_attribute simple_children_attr_description = { .ca_owner = THIS_MODULE, .ca_name = "description", .ca_mode = S_IRUGO, };
static struct configfs_attribute *simple_children_attrs[] = { &simple_children_attr_description, NULL, };
static ssize_t simple_children_attr_show(struct config_item *item, struct configfs_attribute *attr, char *page) { return sprintf(page, "[02-simple-children]\n" "\n" "This subsystem allows the creation of child config_items. These\n" "items have only one attribute that is readable and writeable.\n"); }
static void simple_children_release(struct config_item *item) { kfree(to_simple_children(item)); }
static struct configfs_item_operations simple_children_item_ops = { .release = simple_children_release, .show_attribute = simple_children_attr_show, };
/* * Note that, since no extra work is required on ->drop_item(), * no ->drop_item() is provided. */ static struct configfs_group_operations simple_children_group_ops = { .make_item = simple_children_make_item, };
static struct config_item_type simple_children_type = { .ct_item_ops = &simple_children_item_ops, .ct_group_ops = &simple_children_group_ops, .ct_attrs = simple_children_attrs, .ct_owner = THIS_MODULE, };
static struct configfs_subsystem simple_children_subsys = { .su_group = { .cg_item = { .ci_namebuf = "02-simple-children", .ci_type = &simple_children_type, }, }, };
/* ----------------------------------------------------------------- */
/* * 03-group-children * * This example reuses the simple_children group from above. However, * the simple_children group is not the subsystem itself, it is a * child of the subsystem. Creation of a group in the subsystem creates * a new simple_children group. That group can then have simple_child * children of its own. */
static struct config_group *group_children_make_group(struct config_group *group, const char *name) { struct simple_children *simple_children;
simple_children = kzalloc(sizeof(struct simple_children), GFP_KERNEL); if (!simple_children) return NULL;
config_group_init_type_name(&simple_children->group, name, &simple_children_type);
return &simple_children->group; }
static struct configfs_attribute group_children_attr_description = { .ca_owner = THIS_MODULE, .ca_name = "description", .ca_mode = S_IRUGO, };
static struct configfs_attribute *group_children_attrs[] = { &group_children_attr_description, NULL, };
static ssize_t group_children_attr_show(struct config_item *item, struct configfs_attribute *attr, char *page) { return sprintf(page, "[03-group-children]\n" "\n" "This subsystem allows the creation of child config_groups. These\n" "groups are like the subsystem simple-children.\n"); }
static struct configfs_item_operations group_children_item_ops = { .show_attribute = group_children_attr_show, };
/* * Note that, since no extra work is required on ->drop_item(), * no ->drop_item() is provided. */ static struct configfs_group_operations group_children_group_ops = { .make_group = group_children_make_group, };
static struct config_item_type group_children_type = { .ct_item_ops = &group_children_item_ops, .ct_group_ops = &group_children_group_ops, .ct_attrs = group_children_attrs, .ct_owner = THIS_MODULE, };
static struct configfs_subsystem group_children_subsys = { .su_group = { .cg_item = { .ci_namebuf = "03-group-children", .ci_type = &group_children_type, }, }, };
/* ----------------------------------------------------------------- */
/* * We're now done with our subsystem definitions. * For convenience in this module, here's a list of them all. It * allows the init function to easily register them. Most modules * will only have one subsystem, and will only call register_subsystem * on it directly. */ static struct configfs_subsystem *example_subsys[] = { &childless_subsys.subsys, &simple_children_subsys, &group_children_subsys, NULL, };
static int __init configfs_example_init(void) { int ret; int i; struct configfs_subsystem *subsys;
for (i = 0; example_subsys[i]; i++) { subsys = example_subsys[i];
config_group_init(&subsys->su_group); mutex_init(&subsys->su_mutex); ret = configfs_register_subsystem(subsys); if (ret) { printk(KERN_ERR "Error %d while registering subsystem %s\n", ret, subsys->su_group.cg_item.ci_namebuf); goto out_unregister; } }
return 0;
out_unregister: for (; i >= 0; i--) { configfs_unregister_subsystem(example_subsys[i]); }
return ret; }
static void __exit configfs_example_exit(void) { int i;
for (i = 0; example_subsys[i]; i++) { configfs_unregister_subsystem(example_subsys[i]); } }
module_init(configfs_example_init); module_exit(configfs_example_exit); MODULE_LICENSE("GPL");
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