9p: Make use of iounit for read/write
[linux-2.6.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/ioprio.h>
25 #include <linux/blkdev.h>
26 #include <linux/capability.h>
27 #include <linux/syscalls.h>
28 #include <linux/security.h>
29 #include <linux/pid_namespace.h>
30
31 int set_task_ioprio(struct task_struct *task, int ioprio)
32 {
33         int err;
34         struct io_context *ioc;
35         const struct cred *cred = current_cred(), *tcred;
36
37         rcu_read_lock();
38         tcred = __task_cred(task);
39         if (tcred->uid != cred->euid &&
40             tcred->uid != cred->uid && !capable(CAP_SYS_NICE)) {
41                 rcu_read_unlock();
42                 return -EPERM;
43         }
44         rcu_read_unlock();
45
46         err = security_task_setioprio(task, ioprio);
47         if (err)
48                 return err;
49
50         task_lock(task);
51         do {
52                 ioc = task->io_context;
53                 /* see wmb() in current_io_context() */
54                 smp_read_barrier_depends();
55                 if (ioc)
56                         break;
57
58                 ioc = alloc_io_context(GFP_ATOMIC, -1);
59                 if (!ioc) {
60                         err = -ENOMEM;
61                         break;
62                 }
63                 task->io_context = ioc;
64         } while (1);
65
66         if (!err) {
67                 ioc->ioprio = ioprio;
68                 ioc->ioprio_changed = 1;
69         }
70
71         task_unlock(task);
72         return err;
73 }
74 EXPORT_SYMBOL_GPL(set_task_ioprio);
75
76 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
77 {
78         int class = IOPRIO_PRIO_CLASS(ioprio);
79         int data = IOPRIO_PRIO_DATA(ioprio);
80         struct task_struct *p, *g;
81         struct user_struct *user;
82         struct pid *pgrp;
83         int ret;
84
85         switch (class) {
86                 case IOPRIO_CLASS_RT:
87                         if (!capable(CAP_SYS_ADMIN))
88                                 return -EPERM;
89                         /* fall through, rt has prio field too */
90                 case IOPRIO_CLASS_BE:
91                         if (data >= IOPRIO_BE_NR || data < 0)
92                                 return -EINVAL;
93
94                         break;
95                 case IOPRIO_CLASS_IDLE:
96                         break;
97                 case IOPRIO_CLASS_NONE:
98                         if (data)
99                                 return -EINVAL;
100                         break;
101                 default:
102                         return -EINVAL;
103         }
104
105         ret = -ESRCH;
106         /*
107          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
108          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
109          * in copy_process().
110          */
111         read_lock(&tasklist_lock);
112         switch (which) {
113                 case IOPRIO_WHO_PROCESS:
114                         if (!who)
115                                 p = current;
116                         else
117                                 p = find_task_by_vpid(who);
118                         if (p)
119                                 ret = set_task_ioprio(p, ioprio);
120                         break;
121                 case IOPRIO_WHO_PGRP:
122                         if (!who)
123                                 pgrp = task_pgrp(current);
124                         else
125                                 pgrp = find_vpid(who);
126                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
127                                 ret = set_task_ioprio(p, ioprio);
128                                 if (ret)
129                                         break;
130                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
131                         break;
132                 case IOPRIO_WHO_USER:
133                         if (!who)
134                                 user = current_user();
135                         else
136                                 user = find_user(who);
137
138                         if (!user)
139                                 break;
140
141                         do_each_thread(g, p) {
142                                 if (__task_cred(p)->uid != who)
143                                         continue;
144                                 ret = set_task_ioprio(p, ioprio);
145                                 if (ret)
146                                         goto free_uid;
147                         } while_each_thread(g, p);
148 free_uid:
149                         if (who)
150                                 free_uid(user);
151                         break;
152                 default:
153                         ret = -EINVAL;
154         }
155
156         read_unlock(&tasklist_lock);
157         return ret;
158 }
159
160 static int get_task_ioprio(struct task_struct *p)
161 {
162         int ret;
163
164         ret = security_task_getioprio(p);
165         if (ret)
166                 goto out;
167         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
168         if (p->io_context)
169                 ret = p->io_context->ioprio;
170 out:
171         return ret;
172 }
173
174 int ioprio_best(unsigned short aprio, unsigned short bprio)
175 {
176         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
177         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
178
179         if (aclass == IOPRIO_CLASS_NONE)
180                 aclass = IOPRIO_CLASS_BE;
181         if (bclass == IOPRIO_CLASS_NONE)
182                 bclass = IOPRIO_CLASS_BE;
183
184         if (aclass == bclass)
185                 return min(aprio, bprio);
186         if (aclass > bclass)
187                 return bprio;
188         else
189                 return aprio;
190 }
191
192 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
193 {
194         struct task_struct *g, *p;
195         struct user_struct *user;
196         struct pid *pgrp;
197         int ret = -ESRCH;
198         int tmpio;
199
200         read_lock(&tasklist_lock);
201         switch (which) {
202                 case IOPRIO_WHO_PROCESS:
203                         if (!who)
204                                 p = current;
205                         else
206                                 p = find_task_by_vpid(who);
207                         if (p)
208                                 ret = get_task_ioprio(p);
209                         break;
210                 case IOPRIO_WHO_PGRP:
211                         if (!who)
212                                 pgrp = task_pgrp(current);
213                         else
214                                 pgrp = find_vpid(who);
215                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
216                                 tmpio = get_task_ioprio(p);
217                                 if (tmpio < 0)
218                                         continue;
219                                 if (ret == -ESRCH)
220                                         ret = tmpio;
221                                 else
222                                         ret = ioprio_best(ret, tmpio);
223                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
224                         break;
225                 case IOPRIO_WHO_USER:
226                         if (!who)
227                                 user = current_user();
228                         else
229                                 user = find_user(who);
230
231                         if (!user)
232                                 break;
233
234                         do_each_thread(g, p) {
235                                 if (__task_cred(p)->uid != user->uid)
236                                         continue;
237                                 tmpio = get_task_ioprio(p);
238                                 if (tmpio < 0)
239                                         continue;
240                                 if (ret == -ESRCH)
241                                         ret = tmpio;
242                                 else
243                                         ret = ioprio_best(ret, tmpio);
244                         } while_each_thread(g, p);
245
246                         if (who)
247                                 free_uid(user);
248                         break;
249                 default:
250                         ret = -EINVAL;
251         }
252
253         read_unlock(&tasklist_lock);
254         return ret;
255 }