Re: nanobsd / dd problem?

On Sun, Dec 08, 2013 at 06:31:36PM +0100, Stefan Hegnauer wrote:
> Hi,
> 
>  
> 
> I am using freebsd-current (FreeBSD BUILDMASTER 11.0-CURRENT FreeBSD
> 11.0-CURRENT #0 r259095: Sun Dec  8 10:20:40 CET 2013
> root_at_BUILDMASTER:/usr/obj/usr/src/sys/ASUS  i386) in a VirtualBox as a build
> machine for nanobsd images to be used on pc-engines.ch alix boards. The only
> difference to GENERIC is the inclusion of 'march=geode' and disabling of
> most debugging switches (malloc, Witness etc). Worked like a charm in the
> past.
> 
>  
> 
> Since late summer - sorry, no exact date / svn revision - nanobsd.sh fails
> at the last stage when building the disk image, e.g. with
> 
> ...
> 
> 00:00:25 ### log: /usr/obj/nanobsd.alixpf//_.di
> 
> #
> 
>  
> 
> Looking a bit closer it seems that dd(1) returns with an I/O error whenever
> the input is a file created with mdconfig(8):
> 
> # dd if=/dev/zero of=somebackingfile bs=1k count=5k
> 
> # mdconfig -f somebackingfile -u md0
> 
> # newfs -U /dev/md0
> 
> # dd if=/dev/md0 of=/dev/null
> 
> dd: /dev/md0: Input/output error
> 
> 10241+0 records in
> 
> 10241+0 records out
> 
> 5243392 bytes transferred in 3.240345 secs (1618159 bytes/sec)
> 
>  
> 
> The outputfile in nanobsd.sh seems to be error-free.
It should be one block larger than the right size.
\
> 
> Anyone else seen similar behaviour? How to proceed/fix it?
> 

The following patch should clear the error.

The issue is that kern_physio() incorrectly detects EOF due to incorrect
calculation of bio bio_resid after the bio_length was clipped by the
'excess' code in g_io_check(). Both bio_length and bio_resid appear
to be 0 in the pre-last dd transfer, which starts exactly and the
mediasize, and kern_physio() thinks that it transferred one more block
than was transferred.

I _suspect_ that it was caused by 'excess' code moving in r256880,
but I am really not in the right condition to analyze it.  If somebody
could try the same dd experiment to confirm or deny my suspicion, it
would be useful.

The patch below should be a right thing to do anyway.

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index c23a74b..b7c4d60 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
_at__at_ -3679,7 +3679,6 _at__at_ bufdonebio(struct bio *bip)
 
 	bp = bip->bio_caller2;
 	bp->b_resid = bp->b_bcount - bip->bio_completed;
-	bp->b_resid = bip->bio_resid;	/* XXX: remove */
 	bp->b_ioflags = bip->bio_flags;
 	bp->b_error = bip->bio_error;
 	if (bp->b_error)