[issue1793] tmpfs calling bawrite instead of buwrite

["Alex Hornung \(via DragonFly issue tracker\)" <sinknull@xxxxxxxxxxxxxxxxxxxxx>]

New submission from Alex Hornung <ahornung@gmail.com>:

While testing lvm root mounts, I've encountered an issue with tmpfs. In the 
initrd environment I'm mounting /tmp and /var from tmpfs, and creating a small 
directory structure on them. So far so good, but when lvm creates a bunch of 
files on one of the mount points, the writes fail.
It seems buwrite() should be called, but bawrite is being called due to the 
(uio->uio_segflg == UIO_NOCOPY) check in tmpfs_write.

These screenshots show the symptom:
http://img806.imageshack.us/img806/3512/screenshotdragonflybsdv.png
This second shot shows the relevant flags, etc that are used in the checks 
whenever the tmpfs_write bwrite error message is called.
http://img696.imageshack.us/img696/3512/screenshotdragonflybsdv.png

And this is the commit that introduced that check:
http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/d89ce96a0788eaec175450e8
2a898f3764b99441?hp=b815802035a205b934ffd7e3b2487c7440e7e138

The initrd basically runs an extremely minimalistic /sbin/init that just 
launches another extremely minimalistic /etc/rc, which just does the stuff 
described above. No swap is activated at this time, of course. Also, there 
should be no memory pressure whatsoever.

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messages: 8714
nosy: alexh
status: unread
title: tmpfs calling bawrite instead of buwrite

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DragonFly issue tracker <bugs@lists.dragonflybsd.org>
<http://bugs.dragonflybsd.org/issue1793>
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