On 10/24/2011 10:17 AM, Kevin Wolf wrote:
> I think it's not about "why is it there", but rather about "what is it
> useful for". My interpretation of it is "I do not need the image
> anymore unless the command exits cleanly": VM installations, qemu-img
> conversions, BDRV_O_SNAPSHOT (doesn't do it yet, but it could). Even
> SIGINT and SIGTERM would be excluded from this definition, but they cost
> nothing so it's nice to include them.
I think another common interpretation is: "I don't run this VM in
production but for development. I want the VM to go faster and I can
recreate the image in the unlikely event that power fails during my
work. But it certainly would be nasty."
Fair enough.
But I think that starting to make exceptions for single block drivers
isn't a good idea anyway. If we want bdrv_flush() to write out all
metadata internal to qemu, I think the approach with checking the flag
in drivers calling things like fsync() is better. The common thing is to
do the flush.
I don't know... checking BDRV_O_NO_FLUSH in the drivers rather than in
the generic code sounds like a layering violation. Perhaps what you're
after is a separation of bdrv_co_flush from bdrv_{,co_,aio_}fsync? Then
BDRV_O_NO_FLUSH (better renamed to BDRV_O_NO_FSYNC...) would only
inhibit the latter.
Paolo
