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cgroup: allow a cgroup subsystem to reject a fork

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Add a new cgroup subsystem callback can_fork that conditionally
states whether or not the fork is accepted or rejected by a cgroup
policy. In addition, add a cancel_fork callback so that if an error
occurs later in the forking process, any state modified by can_fork can
be reverted.

Allow for a private opaque pointer to be passed from cgroup_can_fork to
cgroup_post_fork, allowing for the fork state to be stored by each
subsystem separately.

Also add a tagging system for cgroup_subsys.h to allow for CGROUP_<TAG>
enumerations to be be defined and used. In addition, explicitly add a
CGROUP_CANFORK_COUNT macro to make arrays easier to define.

This is in preparation for implementing the pids cgroup subsystem.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Aleksa Sarai
2015-06-09 21:32:09 +10:00
committed by Tejun Heo
parent d770e558e2
commit 7e47682ea5
7 changed files with 133 additions and 9 deletions
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15
include/linux/cgroup.h
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@@ -62,7 +62,12 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *tsk);
void cgroup_fork(struct task_struct *p);
void cgroup_post_fork(struct task_struct *p);
extern int cgroup_can_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]);
extern void cgroup_cancel_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]);
extern void cgroup_post_fork(struct task_struct *p,
void *old_ss_priv[CGROUP_CANFORK_COUNT]);
void cgroup_exit(struct task_struct *p);
int cgroup_init_early(void);
@@ -524,7 +529,13 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry) { return -EINVAL; }
static inline void cgroup_fork(struct task_struct *p) {}
static inline void cgroup_post_fork(struct task_struct *p) {}
static inline int cgroup_can_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT])
{ return 0; }
static inline void cgroup_cancel_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]) {}
static inline void cgroup_post_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]) {}
static inline void cgroup_exit(struct task_struct *p) {}
static inline int cgroup_init_early(void) { return 0; }