The iov_discard_front/back() operations are useful for parsing iovecs
but they modify the array elements. If the original array is needed
after parsing finishes there is currently no way to restore it.
Although g_memdup() can be used before performing destructive
iov_discard_front/back() operations, this is inefficient.
Introduce iov_discard_undo() to restore the array to the state prior to
an iov_discard_front/back() operation.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Message-Id: <20200917094455.822379-2-stefanha@redhat.com>
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