rsync - Mar 2007 - syncronizing file content into device content

I have repeatable cases where a (very large) file contents are the
intended content of a device (partition) of that exact size.  The
target device is already mostly of that content, but a few block
have been changed.  I want to restore the device contents back to
what the file originally was.  I'm trying to find a way to have
rsync's write end open the device as a file and do its thing to
syncronize the content efficiently so I don't have to transfer the
entire content each time by some other means.  But rsync is very
persistent in replacing the device node file with just a regular
file, which because the file is new, causes it to transfer the
content of the original file, filling up the filesystem /dev is on
and needing to restore the device node with mknod.

So, how can I get rsync to syncronize the _content_ of the device
with the _content_ of the source file (or source device)?

I don't even have luck trying to syncronize device content to device
content (e.g. without --devices, which would just replicate the node
and it's major,minor ... it says it is just skipping the non-regular
file naming the source device).  But I do need to do this with the
source being a file, though if I could get device content to device
contnt to work I guess I could fake this with the loopback device.

Any ideas?

-- 
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org)  /  Do not send to the address below |
| first name lower case at ipal.net   /  spamtrap-2007-03-07-1625@ipal.net |
|------------------------------------/-------------------------------------|

On Wed, Mar 07, 2007 at 04:29:36PM -0600, Phil Howard
wrote:
> So, how can I get rsync to syncronize the _content_ of the device
> with the _content_ of the source file (or source device)?
You can't without writing custom code -- for instance, adding an option
to rsync to tell it to treat a block device as a file (which would also
require the use of --inplace).  Otherwise you might look for some other
utility that could patch a single file (I almost suggested trying to use
the rdiff utility in librsync, but it can't update a file in-place).

..wayne..