2.5: syscalls for setting task affinity

The attached patch implements a syscall interface for setting and retrieving a task's CPU affinity (task->cpus_allowed):

	int sched_set_affinity(pid_t pid, unsigned long *new_mask_ptr);

	int sched_get_affinity(pid_t pid)

sched_set_affinity uses the set_cpus_allowed function in Ingo's new scheduler to do all the hard work. Additionally, this patch is based off Ingo's previous syscall affinity patch and my proc-based affinity patch. Much credit to Ingo for this past work and his current scheduler.

Security is enforced: calling user must match task's uid or euid or possess CAP_SYS_NICE.

I think exporting cpus_allowed as a bit mask is the proper user interface for CPU affinity. Certainly more complicated solutions exist, but this should get the job done. I have also updated my proc-based solution although Ingo and others have flamed^Wconvinced me a syscall-based interface is ideal. I agree, mostly on the basis that /proc may not be mounted but I will post an updated proc-based solution anyhow for proper discussion.

Patch is against 2.5.6-pre1. Enjoy,

Robert Love

diff -urN linus/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S
@@ -716,6 +716,8 @@
 	.long SYMBOL_NAME(sys_lremovexattr)
 	.long SYMBOL_NAME(sys_fremovexattr)
 	.long SYMBOL_NAME(sys_tkill)
+	.long SYMBOL_NAME(sys_sched_set_affinity)
+	.long SYMBOL_NAME(sys_sched_get_affinity)	/* 240 */
 
 	.rept NR_syscalls-(.-sys_call_table)/4
 		.long SYMBOL_NAME(sys_ni_syscall)

diff -urN linus/include/asm-i386/unistd.h linux/include/asm-i386/unistd.h
@@ -243,6 +243,8 @@
 #define __NR_lremovexattr	236
 #define __NR_fremovexattr	237
 #define __NR_tkill		238
+#define __NR_sched_set_affinity 239
+#define __NR_sched_get_affinity 240
 
 /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */