linux/fs/kernfs/symlink.c
Ian Kent 7ba0273b2f kernfs: switch kernfs to use an rwsem
The kernfs global lock restricts the ability to perform kernfs node
lookup operations in parallel during path walks.

Change the kernfs mutex to an rwsem so that, when opportunity arises,
node searches can be done in parallel with path walk lookups.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/162642770946.63632.2218304587223241374.stgit@web.messagingengine.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-07-27 09:29:15 +02:00

154 lines
3.3 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* fs/kernfs/symlink.c - kernfs symlink implementation
*
* Copyright (c) 2001-3 Patrick Mochel
* Copyright (c) 2007 SUSE Linux Products GmbH
* Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
*/
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/namei.h>
#include "kernfs-internal.h"
/**
* kernfs_create_link - create a symlink
* @parent: directory to create the symlink in
* @name: name of the symlink
* @target: target node for the symlink to point to
*
* Returns the created node on success, ERR_PTR() value on error.
* Ownership of the link matches ownership of the target.
*/
struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
const char *name,
struct kernfs_node *target)
{
struct kernfs_node *kn;
int error;
kuid_t uid = GLOBAL_ROOT_UID;
kgid_t gid = GLOBAL_ROOT_GID;
if (target->iattr) {
uid = target->iattr->ia_uid;
gid = target->iattr->ia_gid;
}
kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid,
KERNFS_LINK);
if (!kn)
return ERR_PTR(-ENOMEM);
if (kernfs_ns_enabled(parent))
kn->ns = target->ns;
kn->symlink.target_kn = target;
kernfs_get(target); /* ref owned by symlink */
error = kernfs_add_one(kn);
if (!error)
return kn;
kernfs_put(kn);
return ERR_PTR(error);
}
static int kernfs_get_target_path(struct kernfs_node *parent,
struct kernfs_node *target, char *path)
{
struct kernfs_node *base, *kn;
char *s = path;
int len = 0;
/* go up to the root, stop at the base */
base = parent;
while (base->parent) {
kn = target->parent;
while (kn->parent && base != kn)
kn = kn->parent;
if (base == kn)
break;
if ((s - path) + 3 >= PATH_MAX)
return -ENAMETOOLONG;
strcpy(s, "../");
s += 3;
base = base->parent;
}
/* determine end of target string for reverse fillup */
kn = target;
while (kn->parent && kn != base) {
len += strlen(kn->name) + 1;
kn = kn->parent;
}
/* check limits */
if (len < 2)
return -EINVAL;
len--;
if ((s - path) + len >= PATH_MAX)
return -ENAMETOOLONG;
/* reverse fillup of target string from target to base */
kn = target;
while (kn->parent && kn != base) {
int slen = strlen(kn->name);
len -= slen;
memcpy(s + len, kn->name, slen);
if (len)
s[--len] = '/';
kn = kn->parent;
}
return 0;
}
static int kernfs_getlink(struct inode *inode, char *path)
{
struct kernfs_node *kn = inode->i_private;
struct kernfs_node *parent = kn->parent;
struct kernfs_node *target = kn->symlink.target_kn;
int error;
down_read(&kernfs_rwsem);
error = kernfs_get_target_path(parent, target, path);
up_read(&kernfs_rwsem);
return error;
}
static const char *kernfs_iop_get_link(struct dentry *dentry,
struct inode *inode,
struct delayed_call *done)
{
char *body;
int error;
if (!dentry)
return ERR_PTR(-ECHILD);
body = kzalloc(PAGE_SIZE, GFP_KERNEL);
if (!body)
return ERR_PTR(-ENOMEM);
error = kernfs_getlink(inode, body);
if (unlikely(error < 0)) {
kfree(body);
return ERR_PTR(error);
}
set_delayed_call(done, kfree_link, body);
return body;
}
const struct inode_operations kernfs_symlink_iops = {
.listxattr = kernfs_iop_listxattr,
.get_link = kernfs_iop_get_link,
.setattr = kernfs_iop_setattr,
.getattr = kernfs_iop_getattr,
.permission = kernfs_iop_permission,
};