block: make ioc get/put interface more conventional and fix race on alloction
[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/gfp.h>
23 #include <linux/kernel.h>
24 #include <linux/export.h>
25 #include <linux/ioprio.h>
26 #include <linux/blkdev.h>
27 #include <linux/capability.h>
28 #include <linux/syscalls.h>
29 #include <linux/security.h>
30 #include <linux/pid_namespace.h>
31
32 int set_task_ioprio(struct task_struct *task, int ioprio)
33 {
34         int err;
35         struct io_context *ioc;
36         const struct cred *cred = current_cred(), *tcred;
37
38         rcu_read_lock();
39         tcred = __task_cred(task);
40         if (tcred->uid != cred->euid &&
41             tcred->uid != cred->uid && !capable(CAP_SYS_NICE)) {
42                 rcu_read_unlock();
43                 return -EPERM;
44         }
45         rcu_read_unlock();
46
47         err = security_task_setioprio(task, ioprio);
48         if (err)
49                 return err;
50
51         ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
52         if (ioc) {
53                 ioc->ioprio = ioprio;
54                 ioc->ioprio_changed = 1;
55                 put_io_context(ioc);
56         }
57
58         return err;
59 }
60 EXPORT_SYMBOL_GPL(set_task_ioprio);
61
62 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
63 {
64         int class = IOPRIO_PRIO_CLASS(ioprio);
65         int data = IOPRIO_PRIO_DATA(ioprio);
66         struct task_struct *p, *g;
67         struct user_struct *user;
68         struct pid *pgrp;
69         int ret;
70
71         switch (class) {
72                 case IOPRIO_CLASS_RT:
73                         if (!capable(CAP_SYS_ADMIN))
74                                 return -EPERM;
75                         /* fall through, rt has prio field too */
76                 case IOPRIO_CLASS_BE:
77                         if (data >= IOPRIO_BE_NR || data < 0)
78                                 return -EINVAL;
79
80                         break;
81                 case IOPRIO_CLASS_IDLE:
82                         break;
83                 case IOPRIO_CLASS_NONE:
84                         if (data)
85                                 return -EINVAL;
86                         break;
87                 default:
88                         return -EINVAL;
89         }
90
91         ret = -ESRCH;
92         rcu_read_lock();
93         switch (which) {
94                 case IOPRIO_WHO_PROCESS:
95                         if (!who)
96                                 p = current;
97                         else
98                                 p = find_task_by_vpid(who);
99                         if (p)
100                                 ret = set_task_ioprio(p, ioprio);
101                         break;
102                 case IOPRIO_WHO_PGRP:
103                         if (!who)
104                                 pgrp = task_pgrp(current);
105                         else
106                                 pgrp = find_vpid(who);
107                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
108                                 ret = set_task_ioprio(p, ioprio);
109                                 if (ret)
110                                         break;
111                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
112                         break;
113                 case IOPRIO_WHO_USER:
114                         if (!who)
115                                 user = current_user();
116                         else
117                                 user = find_user(who);
118
119                         if (!user)
120                                 break;
121
122                         do_each_thread(g, p) {
123                                 if (__task_cred(p)->uid != who)
124                                         continue;
125                                 ret = set_task_ioprio(p, ioprio);
126                                 if (ret)
127                                         goto free_uid;
128                         } while_each_thread(g, p);
129 free_uid:
130                         if (who)
131                                 free_uid(user);
132                         break;
133                 default:
134                         ret = -EINVAL;
135         }
136
137         rcu_read_unlock();
138         return ret;
139 }
140
141 static int get_task_ioprio(struct task_struct *p)
142 {
143         int ret;
144
145         ret = security_task_getioprio(p);
146         if (ret)
147                 goto out;
148         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
149         if (p->io_context)
150                 ret = p->io_context->ioprio;
151 out:
152         return ret;
153 }
154
155 int ioprio_best(unsigned short aprio, unsigned short bprio)
156 {
157         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
158         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
159
160         if (aclass == IOPRIO_CLASS_NONE)
161                 aclass = IOPRIO_CLASS_BE;
162         if (bclass == IOPRIO_CLASS_NONE)
163                 bclass = IOPRIO_CLASS_BE;
164
165         if (aclass == bclass)
166                 return min(aprio, bprio);
167         if (aclass > bclass)
168                 return bprio;
169         else
170                 return aprio;
171 }
172
173 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
174 {
175         struct task_struct *g, *p;
176         struct user_struct *user;
177         struct pid *pgrp;
178         int ret = -ESRCH;
179         int tmpio;
180
181         rcu_read_lock();
182         switch (which) {
183                 case IOPRIO_WHO_PROCESS:
184                         if (!who)
185                                 p = current;
186                         else
187                                 p = find_task_by_vpid(who);
188                         if (p)
189                                 ret = get_task_ioprio(p);
190                         break;
191                 case IOPRIO_WHO_PGRP:
192                         if (!who)
193                                 pgrp = task_pgrp(current);
194                         else
195                                 pgrp = find_vpid(who);
196                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
197                                 tmpio = get_task_ioprio(p);
198                                 if (tmpio < 0)
199                                         continue;
200                                 if (ret == -ESRCH)
201                                         ret = tmpio;
202                                 else
203                                         ret = ioprio_best(ret, tmpio);
204                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
205                         break;
206                 case IOPRIO_WHO_USER:
207                         if (!who)
208                                 user = current_user();
209                         else
210                                 user = find_user(who);
211
212                         if (!user)
213                                 break;
214
215                         do_each_thread(g, p) {
216                                 if (__task_cred(p)->uid != user->uid)
217                                         continue;
218                                 tmpio = get_task_ioprio(p);
219                                 if (tmpio < 0)
220                                         continue;
221                                 if (ret == -ESRCH)
222                                         ret = tmpio;
223                                 else
224                                         ret = ioprio_best(ret, tmpio);
225                         } while_each_thread(g, p);
226
227                         if (who)
228                                 free_uid(user);
229                         break;
230                 default:
231                         ret = -EINVAL;
232         }
233
234         rcu_read_unlock();
235         return ret;
236 }