A subtlety of this API is that if the @nbytes region traverses a
page boundary, the next __xdr_commit_encode will shift the data item
in the XDR encode buffer. This makes the returned pointer point to
something else, leading to unexpected behavior.
There are a few cases where the caller saves the returned pointer
and then later uses it to insert a computed value into an earlier
part of the stream. This can be safe only if either:
- the data item is guaranteed to be in the XDR buffer's head, and
thus is not ever going to be near a page boundary, or
- the data item is no larger than 4 octets, since XDR alignment
rules require all data items to start on 4-octet boundaries
But that safety is only an artifact of the current implementation.
It would be less brittle if these "safe" uses were eventually
replaced.
Reviewed-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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