* Re: [PATCH 0/2]v2 configfs: symlink() fixes
2008-06-23 22:20 ` [PATCH 0/2]v2 configfs: symlink() fixes Joel Becker
@ 2008-06-24 13:20 ` Louis Rilling
2008-06-24 17:04 ` Joel Becker
0 siblings, 1 reply; 6+ messages in thread
From: Louis Rilling @ 2008-06-24 13:20 UTC (permalink / raw)
To: Joel Becker; +Cc: linux-kernel, ocfs2-devel
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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
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/*
* 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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