Re: [PATCH 01/13] sched: Add 3 new scheduler syscalls to support an extended scheduling parameters ABI

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Feb 14, 2014 at 03:13:22PM +0100, Michael Kerrisk (man-pages) wrote:
> Peter, Dario,
> 
> This is a little late in the day, but I think it's an important point
> to just check before this API goes final.
> 
> > SYNOPSIS
> >         #include <sched.h>
> >
> >         struct sched_attr {
> >                 u32 size;
> >
> >                 u32 sched_policy;
> >                 u64 sched_flags;
> [...]
> >         };
> >
> >         int sched_setattr(pid_t pid, const struct sched_attr *attr);
> >
> >         int sched_getattr(pid_t pid, const struct sched_attr *attr, unsigned int size);
> 
> So, I that there's a flags field in the structure, which allows for
> some extensibility for these calls in the future. However, is it
> worthwhile to consider adding a 'flags' argument in the base signature
> of either of these calls, to allow for some possible extensions in the
> future. (See http://lwn.net/SubscriberLink/585415/7b905c0248a158a2/ ).

Sure why not.. I picked 'unsigned long' for the flags argument; I don't
think there's a real standard for this, I've seen: 'int' 'unsigned int'
and 'unsigned long' flags.

Please holler if there is indeed a preference and I picked the wrong
one.

BTW; do you need more text on the manpage thingy I send you or was that
sufficient?

---
Subject: sched: Add 'flags' argument to sched_{set,get}attr() syscalls

Because of a recent syscall design debate; its deemed appropriate for
each syscall to have a flags argument for future extension; without
immediately requiring new syscalls.

Suggested-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 include/linux/syscalls.h |  6 ++++--
 kernel/sched/core.c      | 11 ++++++-----
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 40ed9e9a77e5..bf41aeb09078 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -281,13 +281,15 @@ asmlinkage long sys_sched_setscheduler(pid_t pid, int policy,
 asmlinkage long sys_sched_setparam(pid_t pid,
 					struct sched_param __user *param);
 asmlinkage long sys_sched_setattr(pid_t pid,
-					struct sched_attr __user *attr);
+					struct sched_attr __user *attr,
+					unsigned long flags);
 asmlinkage long sys_sched_getscheduler(pid_t pid);
 asmlinkage long sys_sched_getparam(pid_t pid,
 					struct sched_param __user *param);
 asmlinkage long sys_sched_getattr(pid_t pid,
 					struct sched_attr __user *attr,
-					unsigned int size);
+					unsigned int size,
+					unsigned long flags);
 asmlinkage long sys_sched_setaffinity(pid_t pid, unsigned int len,
 					unsigned long __user *user_mask_ptr);
 asmlinkage long sys_sched_getaffinity(pid_t pid, unsigned int len,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fb9764fbc537..deeaa54fdf92 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3631,13 +3631,14 @@ SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
  * @pid: the pid in question.
  * @uattr: structure containing the extended parameters.
  */
-SYSCALL_DEFINE2(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr)
+SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
+			       unsigned long, flags)
 {
 	struct sched_attr attr;
 	struct task_struct *p;
 	int retval;
 
-	if (!uattr || pid < 0)
+	if (!uattr || pid < 0 || flags)
 		return -EINVAL;
 
 	if (sched_copy_attr(uattr, &attr))
@@ -3774,8 +3775,8 @@ static int sched_read_attr(struct sched_attr __user *uattr,
  * @uattr: structure containing the extended parameters.
  * @size: sizeof(attr) for fwd/bwd comp.
  */
-SYSCALL_DEFINE3(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
-		unsigned int, size)
+SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
+		unsigned int, size, unsigned long, flags)
 {
 	struct sched_attr attr = {
 		.size = sizeof(struct sched_attr),
@@ -3784,7 +3785,7 @@ SYSCALL_DEFINE3(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	int retval;
 
 	if (!uattr || pid < 0 || size > PAGE_SIZE ||
-	    size < SCHED_ATTR_SIZE_VER0)
+	    size < SCHED_ATTR_SIZE_VER0 || flags)
 		return -EINVAL;
 
 	rcu_read_lock();