setiopri Subroutine
Purpose
Enables the setting of a process I/O priority.
Syntax
short setiopri (ProcessID, IOPriority);
pid_t ProcessID;ushort IOPriorityDescription
The setiopri subroutine sets the I/O scheduling priority of all threads in a process to be a constant. If the target process ID does not match the process ID of the caller, the caller must either be running as root or have an effective and real user ID that matches the target process. A smaller value for the IOPriority designates a higher scheduling priority. Only a few I/O devices support priorities.
Parameters
| Item | Description |
|---|---|
| ProcessID | Specifies the process ID. If this value is -1,
the current process I/O scheduling priority is set to a constant. |
| IOPriority | Specifies the I/O scheduling priority for the process. The IOPriority parameter must be in the range IOPRIORITY_MIN≤IOPriority<IOPRIORITY_MAX. (See the sys/extendio.h file.) |
Return Values
Upon
successful completion, the setiopri subroutine
returns the former I/O scheduling priority of the process just changed.
A returned value of IOPRIORITY_UNSET indicates that
the I/O priority was not set. Otherwise, a value of -1 is
returned and the errno global variable is
set to indicate the error.
Errors
| Item | Description |
|---|---|
| EINVAL | IOPriority value is invalid. |
| EPERM | The calling process is not root. It does not have the same process ID as the target process, and does not have the same real effective user ID as the target process. |
| ESRCH | No process can be found corresponding to the specified ProcessID. |
Implementation Specifics
- Implementation requires an additional field in the proc structure.
- The default setting for process I/O priority is IOPRIORITY_UNSET.
- Once set, process I/O priorities should be inherited across a fork. I/O priorities should not be inherited across an exec.
- The setiopri system call generates an auditing event using audit_svcstart if auditing is enabled on the system (audit_flag is true).