user_namespace.h

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#ifndef _LINUX_USER_NAMESPACE_H
#define _LINUX_USER_NAMESPACE_H

#include <linux/kref.h>
#include <linux/nsproxy.h>
#include <linux/sched.h>
#include <linux/err.h>

#define UID_GID_MAP_MAX_EXTENTS 5

struct uid_gid_map {    /* 64 bytes -- 1 cache line */
    u32 nr_extents;
    struct uid_gid_extent {
        u32 first;
        u32 lower_first;
        u32 count;
    } extent[UID_GID_MAP_MAX_EXTENTS];
};

struct user_namespace {
    struct uid_gid_map  uid_map;
    struct uid_gid_map  gid_map;
    struct uid_gid_map  projid_map;
    struct kref     kref;
    struct user_namespace   *parent;
    kuid_t          owner;
    kgid_t          group;
};

extern struct user_namespace init_user_ns;

#ifdef CONFIG_USER_NS

static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
{
    if (ns)
        kref_get(&ns->kref);
    return ns;
}

extern int create_user_ns(struct cred *new);
extern void free_user_ns(struct kref *kref);

static inline void put_user_ns(struct user_namespace *ns)
{
    if (ns)
        kref_put(&ns->kref, free_user_ns);
}

struct seq_operations;
extern struct seq_operations proc_uid_seq_operations;
extern struct seq_operations proc_gid_seq_operations;
extern struct seq_operations proc_projid_seq_operations;
extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *);
#else

static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
{
    return &init_user_ns;
}

static inline int create_user_ns(struct cred *new)
{
    return -EINVAL;
}

static inline void put_user_ns(struct user_namespace *ns)
{
}

#endif

#endif /* _LINUX_USER_H */