ioprio.h

   1 /*
   2  * Copyright (C) 2012-2020 all contributors <cmogstored-public@yhbt.net>
   3  * License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
   4  */
   5
   6 #include <sys/syscall.h>
   7
   8 #if defined(SYS_ioprio_get) && defined(SYS_ioprio_set)
   9
  10 #ifndef IOPRIO_PRIO_CLASS
  11 #include "ioprio_linux.h"
  12 #endif /* Linux headers */
  13
  14 /*
  15  * specifying which == IOPRIO_WHO_PROCESS and who == 0
  16  * means ioprio works on the current task in Linux.
  17  * This means we can avoid a syscall for gettid()
  18  */
  19
  20 static inline int mog_ioprio_get(int which, int who)
  21 {
  22         return syscall(SYS_ioprio_get, which, who);
  23 }
  24
  25 static inline int mog_ioprio_set(int which, int who, int ioprio)
  26 {
  27         return syscall(SYS_ioprio_set, which, who, ioprio);
  28 }
  29
  30 static int mog_ioprio_drop(void)
  31 {
  32         int rc;
  33         int oldprio = mog_ioprio_get(IOPRIO_WHO_PROCESS, 0);
  34         int newprio;
  35         static int warned;
  36
  37         if (oldprio == -1)
  38                 return -1;
  39
  40         /* don't bother unless it's already best-effort */
  41         switch (IOPRIO_PRIO_CLASS(oldprio)) {
  42         case IOPRIO_CLASS_NONE:
  43                 /*
  44                  * we have to filter out data for ioprio_set to succeed,
  45                  * NONE means the task gets ioprio based on niceness
  46                  */
  47                 oldprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
  48         case IOPRIO_CLASS_BE:
  49                 break; /* OK */
  50         default:
  51                 return -1;
  52         }
  53
  54         newprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 7);
  55         rc = mog_ioprio_set(IOPRIO_WHO_PROCESS, 0, newprio);
  56         if (rc == 0)
  57                 return oldprio;
  58
  59         if (!warned) {
  60                 warned = 1;
  61                 syslog(LOG_WARNING, "failed to drop IO priority: %m");
  62         }
  63         return -1;
  64 }
  65
  66 static void mog_ioprio_restore(int ioprio)
  67 {
  68         static int warned;
  69         int rc = mog_ioprio_set(IOPRIO_WHO_PROCESS, 0, ioprio);
  70
  71         if (rc < 0 && !warned) {
  72                 warned = 1;
  73                 syslog(LOG_WARNING, "failed to restore IO priority: %m");
  74         }
  75 }
  76
  77 #else /* workalikes */
  78 static inline int mog_ioprio_drop(void)
  79 {
  80         return 0;
  81 }
  82
  83 static inline void mog_ioprio_restore(int ioprio)
  84 {
  85 }
  86 #endif