[PATCH] add compat wrapper for get_user_pages_fast

[Jan Kiszka <jan.kiszka@siemens.com>]

Jan Kiszka wrote:
> Xu, Jiajun wrote:
>> Hi,
>> Against latest kvm commit, 9644a6d164e3d6d0532ddb064393293134f31ab2. KVM
>> compile meet error on 2.6.26.2. 
>>
>> [root@kvm-build kernel]# make
>> rm -f include/asm
>> ln -sf asm-x86 include/asm
>> ln -sf asm-x86 include-compat/asm
>> make -C /lib/modules/2.6.26.2/build M=`pwd` \
>>                 LINUXINCLUDE="-I`pwd`/include -Iinclude
>> -Iarch/x86/include -I`pwd`/include-compat \
>>                 -include include/linux/autoconf.h \
>>                 -include `pwd`/x86/external-module-compat.h"
>> make[1]: Entering directory `/usr/src/redhat/BUILD/kernel-2.6.26.2'
>>   CC [M]  /home/build/gitrepo/test/kvm-userspace/kernel/x86/kvm_main.o
>> /home/build/gitrepo/test/kvm-userspace/kernel/x86/kvm_main.c: In
>> function 'gfn_to_pfn':
>> /home/build/gitrepo/test/kvm-userspace/kernel/x86/kvm_main.c:742: error:
>> implicit declaration of function 'get_user_pages_fast'
>> make[3]: ***
>> [/home/build/gitrepo/test/kvm-userspace/kernel/x86/kvm_main.o] Error 1
>> make[2]: *** [/home/build/gitrepo/test/kvm-userspace/kernel/x86] Error 2
>> make[1]: *** [_module_/home/build/gitrepo/test/kvm-userspace/kernel]
>> Error 2
>> make[1]: Leaving directory `/usr/src/redhat/BUILD/kernel-2.6.26.2'
>>
> 
> I can confirm this bug. Looks like Marcelo's get_user_pages_fast patches
> lack corresponding compat wrapping (in kvm-userspace)...

Not sure if this is correct, but here is at least a compile fix.

Note that the original mmem_map locking scope was partly far broader on
older kernels than with Marcelo's patch and this fix now. Could anyone
comment on the correctness?

---------

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 kernel/external-module-compat-comm.h |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Index: b/kernel/external-module-compat-comm.h
===================================================================
--- a/kernel/external-module-compat-comm.h
+++ b/kernel/external-module-compat-comm.h
@@ -531,3 +531,20 @@ struct pci_dev;
 struct pci_dev *pci_get_bus_and_slot(unsigned int bus, unsigned int devfn);
 
 #endif
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,27)
+
+static inline int get_user_pages_fast(unsigned long start, int nr_pages,
+				      int write, struct page **pages)
+{
+	int npages;
+
+	down_read(&current->mm->mmap_sem);
+	npages = get_user_pages(current, current->mm, start, nr_pages, write,
+				0, pages, NULL);
+	up_read(&current->mm->mmap_sem);
+
+	return npages;
+}
+
+#endif