Re: standards/60663: POSIX.1-2024: dd(1) options

["Robert Elz via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR standards/60663; it has been noted by GNATS.

From: Robert Elz <kre%munnari.OZ.AU@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: standards/60663: POSIX.1-2024: dd(1) options
Date: Sat, 29 Aug 2026 02:59:50 +0700

     Date:        Fri, 28 Aug 2026 19:15:01 +0000 (UTC)
     From:        "Taylor R Campbell via gnats" <gnats-admin%NetBSD.org@localhost>
     Message-ID:  <20260828191501.896961A923E%mollari.NetBSD.org@localhost>
 
   |  For some reason I had the idea that using ibs and obs together worked
   |  reliably for this purpose, so I've long been doing stuff like
   |  
   |  progress -zf disk.img.gz dd ibs=64k obs=1m of=dev/rdk42
   |  nc ... | dd ibs=64k obs=1m of=/dev/rsd2
 
 That's fine, and yes, that works, and is reliable.   The only real
 difference between this and the iflags=fullblock together with bs=
 is some less data copying inside dd (at the expense perhaps of a few
 extra read() sys calls, but probably not all that many) in the fullblock
 case.
 
 Where the difference really appears is when you add count=N or skip=M
 options as well, with the fullblock version, you're getting N*B bytes
 of output with -count=N -bs=B, with the ibs/obs version you're getting
 N*avg-read-size (ie: it does N reads, and however much they produce
 is what is written).