arm/173617

[Brian J. McGovern]

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.

  -Brian