RFE: create batch without patching

[Eran Tromer]

Hi,

Currently, rsync --write-batch creates the batch fileset and also
updates the destination. I suggest adding the ability to disable the latter.

Motivation: I wish to sync two large but similar directories residing in
different machines. There is a slow (dial-up) network connection between
the machines, but I have physical access to both. Thus, I would like to
create a batch fileset by transmitting only file lists and checksums
over the slow network, and then transfer the batch fileset on CD-R.

The only essential difficulty I see is that you can't verify the MD5 sum
until you do the actual patching, so such a "blind" batch fileset may be
faulty. In the above scenario that's not a serious problem -- after
patching from the batch fileset on the CD-R, I'll run rsync in normal
mode over the network to fix whatever's broken (or just rely on a large
csum_length, once the MD4 hash checksum_seed issue I explained yesterday
is addressed).

Other plausible motivating scenarios:
* Using a patch fileset for an incremental backup that lets you to
revert to the base copy
* Estimating the bandwidth/time an rsync operation will take before
actually carrying it out
* Preparing several filesets for different scenarios and applying the
appropriate one later


  Eran