On 01/12/2010 01:23 PM, 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PV guests) uses outdated/cached data so some modifications were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.
Not really, pygrub doesn't do any manipulation with file system and
also, it's not working on a life file system. It's called before the
guest boots up to read information about grub.conf/initrd and kernel for
PV guest and after this is read and selected in pygrub then the guest is
booted using the kernel and initrd extracted from the image (after which
the file is closed). Once again, nothing uses write support and it was
added just to make it use O_DIRECT for both read and write operations
but only pygrub uses only read support and O_DIRECT passed here is the
only way to make it use non-cached data.
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