add another field to user_struct

问题

I want to add new field ( to store number of ready process of this user ) to user_struct in file linux-source/kernel/user.c

struct user_struct {
    atomic_t ready_processes; /* I add this field */
    /* not important fields */
}

where to initialize this field correctly ?

回答1:

In order to add a new field to user_struct, you need to do 3 things:

Definition of user_struct is in file sched.h(include/linux/sched.h)
You should add your field in that struct.
```
struct user_struct {
    atomic_t ready_processes; /* I added this line! */
    /*Other fields*/
};
```

In user.c (kernel/user.c) line 51, user_struct is instantiated for root_user globally. Give your field a value here.

struct user_struct root_user = {
    .ready_processes = ATOMIC_INIT(1), /* I added this line! */
    .__count    = ATOMIC_INIT(2),
    .processes  = ATOMIC_INIT(1),
    .files      = ATOMIC_INIT(0),
    .sigpending = ATOMIC_INIT(0),
    .locked_shm     = 0,
    .user_ns    = &init_user_ns,    
};

You're done with initializing your field for root user but you should also initialize it for other users.
For this aim, in user.c, go to the function alloc_uid where new users get allocated and initialized. For example you see there's a line atomic_set(&new->__count, 1); that initializes __count. Add your initialization code beside this.
```
atomic_set(&new->__count, 1);
atomic_set(&new->ready_processes, 1); /* I added this line! */
```

NOTE: It works in linux 2.6.32.62. I'm not sure about other versions but I think it shouldn't be very different.

来源：https://stackoverflow.com/questions/27594865/add-another-field-to-user-struct

标签

kernel

linux-kernel