Hi all,

It seems an instance of `dd`  with only an output file doesn't report the count of records accurately despite bs= being described as influencing both ibs= and obs=

dd'ing from an unstable remote over ssh today I had it continue from the last received block between crashes in preparation for a P2V. The remote had bs=1M set with its in=device and the local instance had bs=1M too with the destination of= device but upon referring to the receiving end's stable count of records I noticed it ignored my bs=1M setting. This were worked around using obs=1M to make the counter show a value I could reliable skip=/seek= with to resume.

I have an example here:

$ dd if=/dev/zero bs=1M count=1 | dd bs=1M of=/dev/null
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0010021 s, 1.0 GB/s
0+16 records in
0+16 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.000771722 s, 1.4 GB/s

This is being experienced on Archlinux with kernel '6.6.4' and package 'core/coreutils 9.4-2'

dd's man page for this distribution shows:

bs=BYTES
              read and write up to BYTES bytes at a time (default: 512); overrides ibs and obs

So I feel it not overriding obs= when invoked with only of= and bs= arguments could be a bug.

Running a single dd with if=source of=dest bs=1M works as intended.

While in my case this isn't a fatal bug working with virtual block devices it could be problematic for use cases which require a proper treatment of block sizes such as tape devices.

Best regards,
Jared