Ubuntu
linux package

aufs doesn't build with (non-standard) config w/o vserver or apparmor

Bug #327337 reported by Peter Cordes on 2009-02-09

This bug report is a duplicate of: Bug #344370: imx51 AppArmor oops during bootup. Edit Remove

Affects		Status	Importance	Assigned to	Milestone
	linux (Ubuntu)	New	Undecided	Unassigned

Bug Description

I'm building a custom kernel, because I want Jaunty's 2.6.28 on Intrepid with a linux-headers-...deb that doesn't Depend: on jaunty's libc. (grrr.) So I figured I might as well customize it for my machine anyway, which is what I used to do back when the 1/2MB of RAM you could save felt like it mattered. :) I mostly followed the instructions at https://help.ubuntu.com/community/Kernel/Compile and
http://blog.avirtualhome.com/2008/10/28/how-to-compile-a-custom-kernel-for-ubuntu-intrepid-using-git/

Anyway, with my custom .config (attached), trying to build 2.6.28-7.20 from the latest Jaunty git repo gives:

/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c: In function 'do_vfsub_mknod':
/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c:166: warning: passing argument 3 of 'vfs_mknod' makes pointer from integer without a cast
/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c:166: error: too few arguments to function 'vfs_mknod'
/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c: In function 'do_vfsub_link':
/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c:191: warning: passing argument 2 of 'vfs_link' from incompatible pointer type
/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c:191: warning: passing argument 3 of 'vfs_link' from incompatible pointer type
/usr/local/src/linux/ubuntu-jaunty/ubuntu/aufs/vfsub.c:191: error: too few arguments to function 'vfs_link'
...

The problem seems to be that the #ifdefs select broken code for my config, but not for Ubuntu's default config. ubuntu/aufs/vfsub.c looks like:

        #ifdef CONFIG_VSERVER // line 160
        err = vfs_mknod(dir, dentry, mode, dev, NULL);
        #elif defined(CONFIG_SECURITY_APPARMOR)
        err = vfs_mknod(dir, dentry, NULL, mode, dev);
        #else
        err = vfs_mknod(dir, dentry, mode, dev);
        #endif // line 167

My .config includes neither CONFIG_VSERVER nor CONFIG_SECURITY_APPARMOR. Ubuntu's kernels ship with a config that includes APPARMOR, but not VSERVER. I haven't figured out where vfs_mknod's prototype comes from, but it doesn't seem to be anywhere in plain text. Probably it's constructed from a macro... vfs_mknod() is defined in fs/namei.c.

There are similar #ifdefs going on with calls to vfs_link, vfs_mkdir, vfs_unlink, etc. Some googling found a patch where someone had made vfs_mknod and so on into macros that added a NULL in the right place depending on what was #defined. That seems more sensible than scattering that extra NULL throughout the aufs code. Although perhaps that's not needed so much anymore, if there are too few arguments in the 4-arg call. Maybe now vfs_mkdir always takes 5 args? Or maybe it shouldn't be #ifdef CONFIG_VSERVER but rather if the vserver patch is applied, if that's how it works. Anyway, my idle speculation is probably not so useful to anyone who's seen this code before. :P

Anyway, this is not strictly an Ubuntu bug, but this is the easiest way to report the bug. So I hope this gets passed along to the right upstream people.