cgroup: add xattr support

This is one of the items in the plumber's wish list.

For use cases:

>> What would the use case be for this?
>
> Attaching meta information to services, in an easily discoverable
> way. For example, in systemd we create one cgroup for each service, and
> could then store data like the main pid of the specific service as an
> xattr on the cgroup itself. That way we'd have almost all service state
> in the cgroupfs, which would make it possible to terminate systemd and
> later restart it without losing any state information. But there's more:
> for example, some very peculiar services cannot be terminated on
> shutdown (i.e. fakeraid DM stuff) and it would be really nice if the
> services in question could just mark that on their cgroup, by setting an
> xattr. On the more desktopy side of things there are other
> possibilities: for example there are plans defining what an application
> is along the lines of a cgroup (i.e. an app being a collection of
> processes). With xattrs one could then attach an icon or human readable
> program name on the cgroup.
>
> The key idea is that this would allow attaching runtime meta information
> to cgroups and everything they model (services, apps, vms), that doesn't
> need any complex userspace infrastructure, has good access control
> (i.e. because the file system enforces that anyway, and there's the
> "trusted." xattr namespace), notifications (inotify), and can easily be
> shared among applications.
>
> Lennart

v7:
- no changes
v6:
- remove user xattr namespace, only allow trusted and security
v5:
- check for capabilities before setting/removing xattrs
v4:
- no changes
v3:
- instead of config option, use mount option to enable xattr support

Original-patch-by: Li Zefan <lizefan@huawei.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Lennart Poettering <lpoetter@redhat.com>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Aristeu Rozanski 2012-08-23 16:53:30 -04:00 committed by Tejun Heo
parent 13af07df9b
commit 03b1cde6b2
2 changed files with 103 additions and 10 deletions

View File

@ -17,6 +17,7 @@
#include <linux/rwsem.h>
#include <linux/idr.h>
#include <linux/workqueue.h>
#include <linux/xattr.h>
#ifdef CONFIG_CGROUPS
@ -216,6 +217,9 @@ struct cgroup {
/* List of events which userspace want to receive */
struct list_head event_list;
spinlock_t event_list_lock;
/* directory xattrs */
struct simple_xattrs xattrs;
};
/*
@ -309,6 +313,9 @@ struct cftype {
/* CFTYPE_* flags */
unsigned int flags;
/* file xattrs */
struct simple_xattrs xattrs;
int (*open)(struct inode *inode, struct file *file);
ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
struct file *file,
@ -394,7 +401,7 @@ struct cftype {
*/
struct cftype_set {
struct list_head node; /* chained at subsys->cftsets */
const struct cftype *cfts;
struct cftype *cfts;
};
struct cgroup_scanner {
@ -406,8 +413,8 @@ struct cgroup_scanner {
void *data;
};
int cgroup_add_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts);
int cgroup_rm_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts);
int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_is_removed(const struct cgroup *cgrp);

View File

@ -276,7 +276,8 @@ inline int cgroup_is_removed(const struct cgroup *cgrp)
/* bits in struct cgroupfs_root flags field */
enum {
ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
ROOT_XATTR, /* supports extended attributes */
};
static int cgroup_is_releasable(const struct cgroup *cgrp)
@ -913,15 +914,19 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
*/
BUG_ON(!list_empty(&cgrp->pidlists));
simple_xattrs_free(&cgrp->xattrs);
kfree_rcu(cgrp, rcu_head);
} else {
struct cfent *cfe = __d_cfe(dentry);
struct cgroup *cgrp = dentry->d_parent->d_fsdata;
struct cftype *cft = cfe->type;
WARN_ONCE(!list_empty(&cfe->node) &&
cgrp != &cgrp->root->top_cgroup,
"cfe still linked for %s\n", cfe->type->name);
kfree(cfe);
simple_xattrs_free(&cft->xattrs);
}
iput(inode);
}
@ -1140,6 +1145,8 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
seq_printf(seq, ",%s", ss->name);
if (test_bit(ROOT_NOPREFIX, &root->flags))
seq_puts(seq, ",noprefix");
if (test_bit(ROOT_XATTR, &root->flags))
seq_puts(seq, ",xattr");
if (strlen(root->release_agent_path))
seq_printf(seq, ",release_agent=%s", root->release_agent_path);
if (clone_children(&root->top_cgroup))
@ -1208,6 +1215,10 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
opts->clone_children = true;
continue;
}
if (!strcmp(token, "xattr")) {
set_bit(ROOT_XATTR, &opts->flags);
continue;
}
if (!strncmp(token, "release_agent=", 14)) {
/* Specifying two release agents is forbidden */
if (opts->release_agent)
@ -1425,6 +1436,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
mutex_init(&cgrp->pidlist_mutex);
INIT_LIST_HEAD(&cgrp->event_list);
spin_lock_init(&cgrp->event_list_lock);
simple_xattrs_init(&cgrp->xattrs);
}
static void init_cgroup_root(struct cgroupfs_root *root)
@ -1769,6 +1781,8 @@ static void cgroup_kill_sb(struct super_block *sb) {
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
simple_xattrs_free(&cgrp->xattrs);
kill_litter_super(sb);
cgroup_drop_root(root);
}
@ -2575,6 +2589,64 @@ static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
}
static struct simple_xattrs *__d_xattrs(struct dentry *dentry)
{
if (S_ISDIR(dentry->d_inode->i_mode))
return &__d_cgrp(dentry)->xattrs;
else
return &__d_cft(dentry)->xattrs;
}
static inline int xattr_enabled(struct dentry *dentry)
{
struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
return test_bit(ROOT_XATTR, &root->flags);
}
static bool is_valid_xattr(const char *name)
{
if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN))
return true;
return false;
}
static int cgroup_setxattr(struct dentry *dentry, const char *name,
const void *val, size_t size, int flags)
{
if (!xattr_enabled(dentry))
return -EOPNOTSUPP;
if (!is_valid_xattr(name))
return -EINVAL;
return simple_xattr_set(__d_xattrs(dentry), name, val, size, flags);
}
static int cgroup_removexattr(struct dentry *dentry, const char *name)
{
if (!xattr_enabled(dentry))
return -EOPNOTSUPP;
if (!is_valid_xattr(name))
return -EINVAL;
return simple_xattr_remove(__d_xattrs(dentry), name);
}
static ssize_t cgroup_getxattr(struct dentry *dentry, const char *name,
void *buf, size_t size)
{
if (!xattr_enabled(dentry))
return -EOPNOTSUPP;
if (!is_valid_xattr(name))
return -EINVAL;
return simple_xattr_get(__d_xattrs(dentry), name, buf, size);
}
static ssize_t cgroup_listxattr(struct dentry *dentry, char *buf, size_t size)
{
if (!xattr_enabled(dentry))
return -EOPNOTSUPP;
return simple_xattr_list(__d_xattrs(dentry), buf, size);
}
static const struct file_operations cgroup_file_operations = {
.read = cgroup_file_read,
.write = cgroup_file_write,
@ -2583,11 +2655,22 @@ static const struct file_operations cgroup_file_operations = {
.release = cgroup_file_release,
};
static const struct inode_operations cgroup_file_inode_operations = {
.setxattr = cgroup_setxattr,
.getxattr = cgroup_getxattr,
.listxattr = cgroup_listxattr,
.removexattr = cgroup_removexattr,
};
static const struct inode_operations cgroup_dir_inode_operations = {
.lookup = cgroup_lookup,
.mkdir = cgroup_mkdir,
.rmdir = cgroup_rmdir,
.rename = cgroup_rename,
.setxattr = cgroup_setxattr,
.getxattr = cgroup_getxattr,
.listxattr = cgroup_listxattr,
.removexattr = cgroup_removexattr,
};
static struct dentry *cgroup_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
@ -2635,6 +2718,7 @@ static int cgroup_create_file(struct dentry *dentry, umode_t mode,
} else if (S_ISREG(mode)) {
inode->i_size = 0;
inode->i_fop = &cgroup_file_operations;
inode->i_op = &cgroup_file_inode_operations;
}
d_instantiate(dentry, inode);
dget(dentry); /* Extra count - pin the dentry in core */
@ -2695,7 +2779,7 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
}
static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
const struct cftype *cft)
struct cftype *cft)
{
struct dentry *dir = cgrp->dentry;
struct cgroup *parent = __d_cgrp(dir);
@ -2705,6 +2789,8 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
umode_t mode;
char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
simple_xattrs_init(&cft->xattrs);
/* does @cft->flags tell us to skip creation on @cgrp? */
if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
return 0;
@ -2745,9 +2831,9 @@ out:
}
static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
const struct cftype cfts[], bool is_add)
struct cftype cfts[], bool is_add)
{
const struct cftype *cft;
struct cftype *cft;
int err, ret = 0;
for (cft = cfts; cft->name[0] != '\0'; cft++) {
@ -2781,7 +2867,7 @@ static void cgroup_cfts_prepare(void)
}
static void cgroup_cfts_commit(struct cgroup_subsys *ss,
const struct cftype *cfts, bool is_add)
struct cftype *cfts, bool is_add)
__releases(&cgroup_mutex) __releases(&cgroup_cft_mutex)
{
LIST_HEAD(pending);
@ -2832,7 +2918,7 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss,
* function currently returns 0 as long as @cfts registration is successful
* even if some file creation attempts on existing cgroups fail.
*/
int cgroup_add_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts)
int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
{
struct cftype_set *set;
@ -2862,7 +2948,7 @@ EXPORT_SYMBOL_GPL(cgroup_add_cftypes);
* Returns 0 on successful unregistration, -ENOENT if @cfts is not
* registered with @ss.
*/
int cgroup_rm_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts)
int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
{
struct cftype_set *set;