X-Git-Url: http://git.annexia.org/?p=libguestfs.git;a=blobdiff_plain;f=src%2Fguestfs.pod;h=7cb05a6c3ac34467f8c7ffa62bc82d4820e9162c;hp=677d94498ac7369fb470486176f7cc14e063e83e;hb=01d62985c3f0234fc0e9e4909c85c6a401c4bfcc;hpb=37e632b7b8e1bd8c9893bb8e3c9a8691c78256a4

diff --git a/src/guestfs.pod b/src/guestfs.pod
index 677d944..7cb05a6 100644
--- a/src/guestfs.pod
+++ b/src/guestfs.pod
@@ -1855,6 +1855,14 @@ The header contains the procedure number (C<guestfs_proc>) which is
 how the receiver knows what type of args structure to expect, or none
 at all.
 
+For functions that take optional arguments, the optional arguments are
+encoded in the C<guestfs_I<foo>_args> structure in the same way as
+ordinary arguments.  A bitmask in the header indicates which optional
+arguments are meaningful.  The bitmask is also checked to see if it
+contains bits set which the daemon does not know about (eg. if more
+optional arguments were added in a later version of the library), and
+this causes the call to be rejected.
+
 The reply message for ordinary functions is:
 
  total length (header + ret,