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Commit 03b1cde6 authored by Aristeu Rozanski's avatar Aristeu Rozanski Committed by Tejun Heo
Browse files

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: default avatarLi 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: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarAristeu Rozanski <aris@redhat.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 13af07df

include/linux/cgroup.h

+10 −3
Original line number Diff line number Diff line
@@ -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);

kernel/cgroup.c

+93 −7
Original line number Diff line number Diff line
@@ -277,6 +277,7 @@ 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_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;