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#include "postgres.h"
#include <unistd.h>
#include <errno.h>
#include <sys/resource.h>
#include "fmgr.h"
#include "miscadmin.h"
#include "storage/proc.h"
#include "storage/procarray.h"
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(set_backend_priority);
PG_FUNCTION_INFO_V1(get_backend_priority);
extern Datum get_backend_priority(PG_FUNCTION_ARGS);
extern Datum set_backend_priority(PG_FUNCTION_ARGS);
Datum
get_backend_priority(PG_FUNCTION_ARGS)
{
int pid = PG_GETARG_INT32(0);
int priority;
int save_errno = errno;
if (!IsBackendPid(pid)) {
ereport(WARNING,
(errmsg("PID %d is not a PostgreSQL server process", pid)));
PG_RETURN_NULL();
}
errno = 0;
priority = getpriority(PRIO_PROCESS, pid);
if (priority == -1) {
/* We need to check errno to determine whether an error has occurred
or if the priority of the process is just '-1'.
*/
if (errno == ESRCH || errno == EINVAL) {
errno = save_errno;
ereport(ERROR,
(errcode(ERRCODE_IO_ERROR),
(errmsg("getpriority() could not find the requested backend"))));
}
}
errno = save_errno;
PG_RETURN_INT32(priority);
}
/* Set the 'nice' priority of the given backend. The priority passed in should
* typically be between 1 and 20, inclusive, since priorities may only
* be adjusted upwards by non-root users. If the backend had been manually
* set (by a root user) to a negative nice value, it may be possible to pass
* in a greater-but-still-negative value as the new priority.
*/
Datum
set_backend_priority(PG_FUNCTION_ARGS)
{
PGPROC *proc;
int pid = PG_GETARG_INT32(0);
int prio = PG_GETARG_INT32(1);
int save_errno = errno;
bool success = true;
if (pid == MyProcPid) {
/* Quick check: if we are setting the priority of our own backend,
* skip permissions checks and chekcs of whether 'pid' is a valid
* backend.
*/
}
else if (!superuser()) {
/*
* Since the user is not superuser, check for matching roles. Trust
* that BackendPidGetProc will return NULL if the pid isn't valid,
* even though the check for whether it's a backend process is below.
* The IsBackendPid check can't be relied on as definitive even if it
* was first. The process might end between successive checks
* regardless of their order. There's no way to acquire a lock on an
* arbitrary process to prevent that.
*/
proc = BackendPidGetProc(pid);
if (proc == NULL) {
/*
* This is just a warning so a loop-through-resultset will not
* abort if one backend terminated on its own during the run
*/
ereport(WARNING,
(errmsg("PID %d is not a PostgreSQL server process", pid)));
success = false;
}
else if (proc->roleId != GetUserId())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
(errmsg("must be superuser to nice arbitrary backends"))));
/* Otherwise, the backend PID is valid and our user is allowed
* to set its priority.
*/
}
else if (!IsBackendPid(pid))
{
ereport(WARNING,
(errmsg("PID %d is not a PostgreSQL server process", pid)));
success = false;
}
if (success) {
errno = 0;
if (setpriority(PRIO_PROCESS, pid, prio) == 0) {
ereport(NOTICE,
(errmsg("Set priority of backend %d to %d", pid, prio)));
}
else {
if (errno == ESRCH || errno == EINVAL) {
errno = save_errno;
ereport(ERROR,
(errcode(ERRCODE_IO_ERROR),
(errmsg("setpriority(): could not find the requested backend"))));
}
else {
/* Assume EPERM or EACCES */
ereport(WARNING,
(errmsg("setpriority(): permission denied")));
success = false;
}
}
}
errno = save_errno;
PG_RETURN_BOOL(success);
}
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