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Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: use O_DIRECT to open disk images for IDE [and 1 more messages]
Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional:
use O_DIRECT to open disk images for IDE [and 1 more messages]"):
> In qemu-xen you can easily have this sequence of calls:
>
> bdrv_co_writev -> qcow2_co_writev -> qcow2_alloc_cluster_offset ->
> get_cluster_table -> qcow2_grow_l1_table -> bdrv_pwrite_sync
...
> In qemu-xen-traditional they would become:
>
> qcow_aio_write_cb -> alloc_cluster_offset -> get_cluster_table ->
> grow_l1_table -> bdrv_pwrite
>
>
> The key piece of information is that bdrv_pwrite_sync issues a
> bdrv_flush if the file was opened as WB, while bdrv_pwrite does not.
Yes, but why does this matter ? If the guest cares about the data
then it will either turn off caching entirely, or issue an explicit
flush operation, which will translate into a bdrv_flush. So the flush
will happen.
Ian.
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