arm/173617

[Ian Lepore]

On Mon, 2013-03-04 at 16:55 -0500, Brian J. McGovern wrote:
> I have been chasing down a disk write problem my OpenRD. In my research, I
> ran across arm/173617, which discusses file corruption while downloading ports
> via fetch, which is how I first noticed the issue. However, contrary to the PR,
> the issues does not appear to be in the network interface, but rather on the
> writing of the file to disk. The problem appears global - I've tested SATA,
> USB (umass), and SD/MMC interfaces. I've also had problems with NFS mounts in 
> the past, but have not verified that the issues are the same.
> 
> I have not chased down a particular size, but "small" writes (e.g. a config
> file, .c file, etc.) appear to work correctly at all times. "Large" writes
> (I usually see it on files a MB or larger, but this may be a function of 
> opportunity) will typically see some number of bytes set to zero. To reproduce
> the problem, I wrote a short application that writes sequentially incrementing
> 64-bit integers out to disk. (e.g. 0, 1, 2, 3...), and one that reads them 
> back.
> 
> The result matrix clearly showed the problem is on the write side - writing
> files on other systems and reading them back on the OpenRD works fine. Writing
> them on the OpenRD causes read back failures, both on the OpenRD _and_ other
> hosts. I have also found that setting the file handle O_SYNC (or mounting
> the filesystem in sync mode) eliminates the problem.
> 
> Has anyone seen/fixed this problem? I'd hate to waste much more time with it
> if its a known problem, or there is a closed PR I haven't found yet.
> 

You didn't say what version of freebsd you're working with.  I saw a
problem like that a while back on my similar DreamPlug; the symptom was
random chunks of corruption that were always 32 bytes of wrong data
each.  I think the fix for that was to disable cache write-allocate on
sheeva chipsets; that fix came into -current along with all the armv6
changes, but I have it as a separate patch too.

-- Ian