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Subject[PATCH v3 3/3] cgroup: add xattr support
From: Li Zefan <lizefan@huawei.com>

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

v3:
- instead of config option, use mount option to enable xattr support

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>

---
include/linux/cgroup.h | 13 ++++-
kernel/cgroup.c | 118 ++++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 112 insertions(+), 19 deletions(-)
--- linus-2.6.orig/include/linux/cgroup.h 2012-07-02 10:21:58.055646941 -0400
+++ linus-2.6/include/linux/cgroup.h 2012-07-02 10:22:22.012584730 -0400
@@ -17,6 +17,7 @@ * Copyright (C) 2004-2006 Silicon Grap
#include <linux/rwsem.h>
#include <linux/idr.h>
#include <linux/workqueue.h>
+#include <linux/xattr.h>

#ifdef CONFIG_CGROUPS

@@ -216,6 +217,9 @@ * count users of this cgroup. >0 means
/* List of events which userspace want to receive */
struct list_head event_list;
spinlock_t event_list_lock;
+
+ /* directory xattrs */
+ struct simple_xattrs xattrs;
};

/*
@@ -312,6 +316,9 @@ * If not 0, file mode is set to this v
/* 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,
@@ -397,7 +404,7 @@ * Returns 0 or -ve error code.
*/
struct cftype_set {
struct list_head node; /* chained at subsys->cftsets */
- const struct cftype *cfts;
+ struct cftype *cfts;
};

struct cgroup_scanner {
@@ -409,8 +416,8 @@ 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);

--- linus-2.6.orig/kernel/cgroup.c 2012-07-02 10:21:58.059646980 -0400
+++ linus-2.6/kernel/cgroup.c 2012-07-02 10:22:22.017584857 -0400
@@ -276,7 +276,8 @@ inline int cgroup_is_removed(const struc

/* 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)
@@ -916,15 +917,19 @@ static void cgroup_diput(struct dentry *
*/
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);
}
@@ -1149,6 +1154,8 @@ static int cgroup_show_options(struct se
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))
@@ -1217,6 +1224,10 @@ memset(opts, 0, sizeof(*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)
@@ -1434,6 +1445,7 @@ static void init_cgroup_housekeeping(str
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)
@@ -1779,6 +1791,8 @@ ret = rebind_subsystems(root, 0);
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);

+ simple_xattrs_free(&cgrp->xattrs);
+
kill_litter_super(sb);
cgroup_drop_root(root);
}
@@ -2585,19 +2599,89 @@ static int cgroup_rename(struct inode *o
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_USER_PREFIX, XATTR_USER_PREFIX_LEN) ||
+ !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,
- .llseek = generic_file_llseek,
- .open = cgroup_file_open,
- .release = cgroup_file_release,
+ .read = cgroup_file_read,
+ .write = cgroup_file_write,
+ .llseek = generic_file_llseek,
+ .open = cgroup_file_open,
+ .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,
+ .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, struct nameidata *nd)
@@ -2645,6 +2729,7 @@ static int cgroup_create_file(struct den
} 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 */
@@ -2705,7 +2790,7 @@ umode_t mode = 0;
}

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);
@@ -2716,6 +2801,7 @@ static int cgroup_add_file(struct cgroup
char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };

cft->subsys = subsys;
+ simple_xattrs_init(&cft->xattrs);

/* does @cft->flags tell us to skip creation on @cgrp? */
if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
@@ -2757,9 +2843,9 @@ 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++) {
@@ -2793,7 +2879,7 @@ 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);
@@ -2844,7 +2930,7 @@ * Returns 0 on successful registration,
* 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;

@@ -2874,7 +2960,7 @@ 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;



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