On 01/12/2010 04:16 PM, Eric Sandeen wrote:
Christoph Hellwig wrote:
On Tue, Jan 12, 2010 at 01:15:49PM +0100, Michal Novotny wrote:
I don't really know if I see your point but the thing here is that there
was no way to open a file directly (ie. using O_DIRECT). The direct
write support has been added only to make it possible to use both read
and write directly. The main reason to create this patch was to add
direct read support and flush capability won't help me at all. I am
working in Red Hat, Virtualization team on Xen so I am really not that
much familiar with file systems but what I needed was an option to read
the data directly (using O_DIRECT) in e2fsprogs. One bug was about
pygrub (Python version of GRUB of Xen PV guests that is internally using
e2fsprogs functionality to access data on ext2/3/4 partition to boot the
PV guests) uses outdated/cached data so some modifications were
necessary to open everything directly...
So to get things staigt: you're using e2fsprogs to manipulate a life
filesystem and thing using O_DIRECT saves your ass? I think you need to
rething your model of operation fundamentally in that case.
Christoph -
It's my understanding that nobody is doing concurrent access.
Eric,
indeed, no concurrent accesses are happening that time. The guests file
system seems to be cached since after dropping caches in host (dom0) it
is reported to work correctly.
If the host reads the block device via pygrub to boot the guest,
the guest while running updates the same device when installing
a new kernel (either through the fs, or by writing to the bdev;
probably the former...), and then the guest shuts down - is there
something which will sync the host's cache (cached from the
prior read) with the updates from the guest?
It appears that the data are cached in host (dom0) and another access
(after guest update/shutdown sequence) makes dom0 still provide old
(cached) data and not the current (newest) data.
Michal
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