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Re: [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes.


--On 19 March 2013 15:13:29 +0000 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:

Therefore I think that the current change is not safe, but it is pretty
easy to make it safe.
You just need to move the call to blk_open from blk_init to blk_connect.
Actually you can move most of blk_init to blk_connect, you just need to
keep the 4 xenstore_write_be_int at the end of the function.

The final of these 4 writes in blk_init is:

   xenstore_write_be_int(&blkdev->xendev, "sectors",
                         blkdev->file_size / blkdev->file_blk);

and blkdev->filesize comes from bdrv_getlength(blkdev->bs), and that
requires (I think) bdrv_open to have been called. Can these
4 writes move safely to blk_connect? Or can we write the sectors
count as (say) 0 here and fix it later in blk_connect? The remainder
look ok.

Alex Bligh

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