On Fri, Feb 12, 2021 at 06:58:53PM +0800, Shuo A Liu wrote: > Hi Greg, > > On Fri 12.Feb'21 at 8:52:33 +0100, Greg Kroah-Hartman wrote: > > On Fri, Feb 12, 2021 at 12:57:24PM +0800, shuo.a.liu@xxxxxxxxx wrote: > > > From: Shuo Liu <shuo.a.liu@xxxxxxxxx> > > > > > > vCPU removing code depends on CONFIG_HOTPLUG_CPU as it uses remove_cpu() > > > and add_cpu(). Make the vCPU removing interface building with > > > CONFIG_HOTPLUG_CPU. > > > > > > ../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); > > > > > > Fixes: 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to control vCPU") > > > Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > > > Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> # build-tested > > > Signed-off-by: Shuo Liu <shuo.a.liu@xxxxxxxxx> > > > --- > > > drivers/virt/acrn/hsm.c | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/drivers/virt/acrn/hsm.c b/drivers/virt/acrn/hsm.c > > > index 1f6b7c54a1a4..e340788aacdf 100644 > > > --- a/drivers/virt/acrn/hsm.c > > > +++ b/drivers/virt/acrn/hsm.c > > > @@ -372,6 +372,7 @@ static int acrn_dev_release(struct inode *inode, struct file *filp) > > > return 0; > > > } > > > > > > +#ifdef CONFIG_HOTPLUG_CPU > > > static ssize_t remove_cpu_store(struct device *dev, > > > struct device_attribute *attr, > > > const char *buf, size_t count) > > > @@ -403,9 +404,12 @@ static ssize_t remove_cpu_store(struct device *dev, > > > return ret; > > > } > > > static DEVICE_ATTR_WO(remove_cpu); > > > +#endif > > > > > > static struct attribute *acrn_attrs[] = { > > > +#ifdef CONFIG_HOTPLUG_CPU > > > &dev_attr_remove_cpu.attr, > > > +#endif > > > NULL > > > }; > > > > > > > > > > Shouldn't the real solution for this be that remove_cpu() and add_cpu() > > have function prototypes for when this is not enabled in the kernel > > build? > > Something like this in linux/cpu.h? > > 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 */ > > > > > > Putting #ifdef in .c files like this is not a good idea at all. > > > > Then, at runtime, you can determine if you need to create this sysfs > > file or not, as you do not want to expose it to userspace if the kernel > > can not handle it, right? > > Right. I don't want to expose the sysfs to userspace if the kernel built > w/o CONFIG_HOTPLUG_CPU. But how to implement that if #ifdef is not used? > misc_register() creates sysfs with .groups (acrn_attr_groups) > unconditionally, then userspace can see the interface even it doesn't > work. Use the is_visible() callback for your attribute group. thanks, greg k-h