The SPL_AC_ATOMIC_SPINLOCK, SPL_AC_TYPE_ATOMIC64_CMPXCHG, and
SPL_AC_TYPE_ATOMIC64_XCHG were all directly including the
'asm/atomic.h' header. As of Linux 3.4 this header was removed
which results in a build failure.
The right thing to do is include 'linux/atomic.h' however we
can't safely do this because it doesn't exist in 2.6.26 kernels.
Therefore, we include 'linux/fs.h' which in turn includes the
correct atomic header regardless of the kernel version.
When these incorrect APIs are used in ZFS the following build
arc.c:791:80: warning: '__ret' may be used uninitialized
in this function [-Wuninitialized]
arc.c:791:1875: error: call to '__cmpxchg_wrong_size'
declared with attribute error: Bad argument size for cmpxchg
Since this is all Linux 2.6.24 compatibility code there's
an argument to be made that it should be removed because
kernels this old are not supported. However, because we're
so close to a release I'm going to leave it in place for now.
Signed-off-by: Brian Behlendorf <email@example.com>