linux-kernel - [PATCH v2 1/2] cpu/hotplug: Fix build error of using {add,remove}_cpu() with !CONFIG

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Date:   Sat, 13 Feb 2021 00:55:18 +0800
From:   shuo.a.liu@...el.com
To:     linux-next@...r.kernel.org
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Randy Dunlap <rdunlap@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Qais Yousef <qais.yousef@....com>,
        linux-kernel@...r.kernel.org, Shuo Liu <shuo.a.liu@...el.com>
Subject: [PATCH v2 1/2] cpu/hotplug: Fix build error of using {add,remove}_cpu() with !CONFIG_SMP

From: Shuo Liu <shuo.a.liu@...el.com>

279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to
control vCPU") introduced {add,remove}_cpu() usage and it hit below
error with !CONFIG_SMP:

../drivers/virt/acrn/hsm.c: In function ‘remove_cpu_store’:
../drivers/virt/acrn/hsm.c:389:3: error: implicit declaration of function ‘remove_cpu’; [-Werror=implicit-function-declaration]
   remove_cpu(cpu);

../drivers/virt/acrn/hsm.c:402:2: error: implicit declaration of function ‘add_cpu’; [-Werror=implicit-function-declaration]
   add_cpu(cpu);

Add add_cpu() function prototypes with !CONFIG_SMP and remove_cpu() with
!CONFIG_HOTPLUG_CPU for such usage.

Fixes: 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to control vCPU")
Reported-by: Randy Dunlap <rdunlap@...radead.org>
Signed-off-by: Shuo Liu <shuo.a.liu@...el.com>
---
I followed Greg's idea that add {add,remove}_cpu() functions prototypes.
The v2 solution is different from the v1, so i removed Randy's Acked-by.
Randy, please help have a look on v2.

v2:
  - Drop the #ifdef in .c solution. Add {add,remove}_cpu() prototypes. (Suggested by Greg)

 include/linux/cpu.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 3aaa0687e8df..94a578a96202 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -108,6 +108,8 @@ static inline void cpu_maps_update_done(void)
 {
 }
 
+static inline int add_cpu(unsigned int cpu) { return 0;}
+
 #endif /* CONFIG_SMP */
 extern struct bus_type cpu_subsys;
 
@@ -137,6 +139,7 @@ static inline int  cpus_read_trylock(void) { return true; }
 static inline void lockdep_assert_cpus_held(void) { }
 static inline void cpu_hotplug_disable(void) { }
 static inline void cpu_hotplug_enable(void) { }
+static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
 static inline void smp_shutdown_nonboot_cpus(unsigned int primary_cpu) { }
 #endif	/* !CONFIG_HOTPLUG_CPU */
 

base-commit: 671176b0016c80b3943cb5387312c886aba3308d
-- 
2.28.0