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Re: [Qemu-devel] [PATCH] ide.c make write cacheing controllable by guest
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] [PATCH] ide.c make write cacheing controllable by guest |
Date: |
Tue, 26 Feb 2008 12:49:56 +0000 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Ian Jackson wrote:
> > Ideally, the host would provide variation of fdatasync() which flushes
> > data to hard storage in the same way that kernel filesystem journal
> > writes can do, and Qemu would use that.
>
> Another question arises: do we want bdrv_flush to call (eventually)
> fsync or fdatasync ? If the latter we need to make sure that we call
> fsync instead when necessary, for example when a cow file is extended.
I'm imagining that fdatasync() will flush the necessary metadata,
including file size, when a file is extended. As would O_DSYNC.
I could be wrong, but I think it's expected to do that, as I recall
VxFS doing something like that with O_DSYNC.
Then again, even if it's meant to, that doesn't mean it does...
-- Jamie