Add ZFS specific mmap() checks

Under Linux the VFS handles virtually all of the mmap() access
checks.  Filesystem specific checks are left to be handled in
the .mmap() hook and normally there arn't any.

However, ZFS provides a few attributes which can influence the
mmap behavior and should be honored.  Note, currently the code
to modify these attributes has not been implemented under Linux.

* ZFS_IMMUTABLE | ZFS_READONLY | ZFS_APPENDONLY: when any of these
  attributes are set a file may not be mmaped with write access.

* ZFS_AV_QUARANTINED: when set a file file may not be mmaped with
  read or exec access.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/zfs_vnops.h

@@ -74,6 +74,8 @@ extern int zfs_setsecattr(struct inode *ip, vsecattr_t *vsecp, int flag,
 extern int zfs_getpage(struct inode *ip, struct page *pl[], int nr_pages);
 extern int zfs_putpage(struct page *page, struct writeback_control *wbc,
     void *data);
+extern int zfs_map(struct inode *ip, offset_t off, caddr_t *addrp,
+    size_t len, unsigned long vm_flags);
 
 #ifdef	__cplusplus
 }