Guest additions module vboxguest fails to load with 'unresolved symbol vunmap'

[Martin Cockerell]

Module vboxguest fails to load due to 'unresolved symbol vunmap' in Linux guest with kernel version 2.4.20 - the vunmap system function is not available at this kernel level.

The guest additions source code contains conditional compilation directives to support various kernel levels (including above/below 2.4.22, the level at which the vmap/vunmap functions become available) but these are incomplete in the source file memobj-r0drv-linux.c. Specifically, although the use of vmap and vunmap is bypassed in several places, vunmap is still called in function rtR0MemObjNativeFree for memory types RTR0MEMOBJTYPE_RES_VIRT and RTR0MEMOBJTYPE_MAPPING.

Commenting out these vunmap calls and rebuilding allows vboxguest to load and the shared folder functionality to work.

[Martin Cockerell]

memobj-r0drv-linux.c with added printk calls for debugging

[Martin Cockerell]

Extract from dmesg output showing debugging messages

[Martin Cockerell]

I added printk calls to memobj-r0drv-linux.c to aid debugging - the KERN_DEBUG messages are prefixed 'MJC' for ease of recognition.

The dmesg output shows that rtR0MemObjNativeMapKernel calls rtR0MemObjNew for type RTR0MEMOBJTYPE_MAPPING when Guest Additions is started.

When Guest Additions is stopped the dmesg output shows that rtR0MemObjNativeFree is called for type RTR0MEMOBJTYPE_MAPPING and the 'vunmap' code path is followed.

[Frank Mehnert]

Actually we don't support all 2.4 kernels. The oldest guest kernel which is supported by VirtualBox is the RHEL3 kernel which is 2.4.21 with some modifications, among them vmalloc / vfree.