Checksum filter rule

[teramide]

Hello,

I'm using rsync to make backups. In my dataset, however, there are a few 
encrypted Truecrypt volumes. When these files are modified, the content 
changes but the timestamps are not updated. Thus, rsync will not sync 
these files by default. I would like to keep the behavior of Truecrypt 
and have rsync update the files correctly.
Using the --checksum option comes to mind in this case. However, this 
will cause rsync to calculate a checksum for *all* files of my dataset, 
slowing down the backup enormously. The workaround I have come up with 
is to first execute an rsync without the --checksum option on the whole 
dataset, and then another rsync with --checksum only for the encrypted 
files. This is significantly faster, but still not optimal since I'm 
running rsync twice on the same dataset.
Is there any better way to do this? I have searched the archives of the 
rsync mailing list, but could not come up with a better solution.
This has prompted me to make following suggestion: would it be possible 
to add filter rules for calculating checksums? Just like you would have 
rules to include, exclude and merge files, you could define filter rules 
for files that have to be checked with a checksum. I could imagine other 
uses for this, for example to force an extra check (e.g. against 
corruption) on very important files in a dataset, etc.
(Please do also make suggestions if you find a way to improve the 
procedure in my specific case.)

Thanks!


(PS: Sorry if this is a resend, the confirmation mail to subscribe to 
the mailing list was not clear about whether my first mail would be 
posted or not, cfr. 
"https://lists.samba.org/archive/rsync/2011-December/027205.html")