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[linux-3.10.git] / fs / ioprio.c
1 /*
2  * fs/ioprio.c
3  *
4  * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
5  *
6  * Helper functions for setting/querying io priorities of processes. The
7  * system calls closely mimmick getpriority/setpriority, see the man page for
8  * those. The prio argument is a composite of prio class and prio data, where
9  * the data argument has meaning within that class. The standard scheduling
10  * classes have 8 distinct prio levels, with 0 being the highest prio and 7
11  * being the lowest.
12  *
13  * IOW, setting BE scheduling class with prio 2 is done ala:
14  *
15  * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
16  *
17  * ioprio_set(PRIO_PROCESS, pid, prio);
18  *
19  * See also Documentation/block/ioprio.txt
20  *
21  */
22 #include <linux/kernel.h>
23 #include <linux/ioprio.h>
24 #include <linux/blkdev.h>
25 #include <linux/capability.h>
26 #include <linux/syscalls.h>
27 #include <linux/security.h>
28
29 static int set_task_ioprio(struct task_struct *task, int ioprio)
30 {
31         int err;
32         struct io_context *ioc;
33
34         if (task->uid != current->euid &&
35             task->uid != current->uid && !capable(CAP_SYS_NICE))
36                 return -EPERM;
37
38         err = security_task_setioprio(task, ioprio);
39         if (err)
40                 return err;
41
42         task_lock(task);
43
44         task->ioprio = ioprio;
45
46         ioc = task->io_context;
47         /* see wmb() in current_io_context() */
48         smp_read_barrier_depends();
49
50         if (ioc)
51                 ioc->ioprio_changed = 1;
52
53         task_unlock(task);
54         return 0;
55 }
56
57 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
58 {
59         int class = IOPRIO_PRIO_CLASS(ioprio);
60         int data = IOPRIO_PRIO_DATA(ioprio);
61         struct task_struct *p, *g;
62         struct user_struct *user;
63         int ret;
64
65         switch (class) {
66                 case IOPRIO_CLASS_RT:
67                         if (!capable(CAP_SYS_ADMIN))
68                                 return -EPERM;
69                         /* fall through, rt has prio field too */
70                 case IOPRIO_CLASS_BE:
71                         if (data >= IOPRIO_BE_NR || data < 0)
72                                 return -EINVAL;
73
74                         break;
75                 case IOPRIO_CLASS_IDLE:
76                         if (!capable(CAP_SYS_ADMIN))
77                                 return -EPERM;
78                         break;
79                 default:
80                         return -EINVAL;
81         }
82
83         ret = -ESRCH;
84         /*
85          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
86          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
87          * in copy_process().
88          */
89         read_lock(&tasklist_lock);
90         switch (which) {
91                 case IOPRIO_WHO_PROCESS:
92                         if (!who)
93                                 p = current;
94                         else
95                                 p = find_task_by_pid(who);
96                         if (p)
97                                 ret = set_task_ioprio(p, ioprio);
98                         break;
99                 case IOPRIO_WHO_PGRP:
100                         if (!who)
101                                 who = process_group(current);
102                         do_each_task_pid(who, PIDTYPE_PGID, p) {
103                                 ret = set_task_ioprio(p, ioprio);
104                                 if (ret)
105                                         break;
106                         } while_each_task_pid(who, PIDTYPE_PGID, p);
107                         break;
108                 case IOPRIO_WHO_USER:
109                         if (!who)
110                                 user = current->user;
111                         else
112                                 user = find_user(who);
113
114                         if (!user)
115                                 break;
116
117                         do_each_thread(g, p) {
118                                 if (p->uid != who)
119                                         continue;
120                                 ret = set_task_ioprio(p, ioprio);
121                                 if (ret)
122                                         goto free_uid;
123                         } while_each_thread(g, p);
124 free_uid:
125                         if (who)
126                                 free_uid(user);
127                         break;
128                 default:
129                         ret = -EINVAL;
130         }
131
132         read_unlock(&tasklist_lock);
133         return ret;
134 }
135
136 static int get_task_ioprio(struct task_struct *p)
137 {
138         int ret;
139
140         ret = security_task_getioprio(p);
141         if (ret)
142                 goto out;
143         ret = p->ioprio;
144 out:
145         return ret;
146 }
147
148 int ioprio_best(unsigned short aprio, unsigned short bprio)
149 {
150         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
151         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
152
153         if (!ioprio_valid(aprio))
154                 return bprio;
155         if (!ioprio_valid(bprio))
156                 return aprio;
157
158         if (aclass == IOPRIO_CLASS_NONE)
159                 aclass = IOPRIO_CLASS_BE;
160         if (bclass == IOPRIO_CLASS_NONE)
161                 bclass = IOPRIO_CLASS_BE;
162
163         if (aclass == bclass)
164                 return min(aprio, bprio);
165         if (aclass > bclass)
166                 return bprio;
167         else
168                 return aprio;
169 }
170
171 asmlinkage long sys_ioprio_get(int which, int who)
172 {
173         struct task_struct *g, *p;
174         struct user_struct *user;
175         int ret = -ESRCH;
176         int tmpio;
177
178         read_lock(&tasklist_lock);
179         switch (which) {
180                 case IOPRIO_WHO_PROCESS:
181                         if (!who)
182                                 p = current;
183                         else
184                                 p = find_task_by_pid(who);
185                         if (p)
186                                 ret = get_task_ioprio(p);
187                         break;
188                 case IOPRIO_WHO_PGRP:
189                         if (!who)
190                                 who = process_group(current);
191                         do_each_task_pid(who, PIDTYPE_PGID, p) {
192                                 tmpio = get_task_ioprio(p);
193                                 if (tmpio < 0)
194                                         continue;
195                                 if (ret == -ESRCH)
196                                         ret = tmpio;
197                                 else
198                                         ret = ioprio_best(ret, tmpio);
199                         } while_each_task_pid(who, PIDTYPE_PGID, p);
200                         break;
201                 case IOPRIO_WHO_USER:
202                         if (!who)
203                                 user = current->user;
204                         else
205                                 user = find_user(who);
206
207                         if (!user)
208                                 break;
209
210                         do_each_thread(g, p) {
211                                 if (p->uid != user->uid)
212                                         continue;
213                                 tmpio = get_task_ioprio(p);
214                                 if (tmpio < 0)
215                                         continue;
216                                 if (ret == -ESRCH)
217                                         ret = tmpio;
218                                 else
219                                         ret = ioprio_best(ret, tmpio);
220                         } while_each_thread(g, p);
221
222                         if (who)
223                                 free_uid(user);
224                         break;
225                 default:
226                         ret = -EINVAL;
227         }
228
229         read_unlock(&tasklist_lock);
230         return ret;
231 }
232