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[Xen-devel] Re: [rfc] [patch] grant_entry.flags accessors

On 27 Jun 2006, at 16:06, Hollis Blanchard wrote:

In the couple cases so far, we know that even though the field is only
one or two bytes, it's actually safe to do a four-byte load/store to it
because the containing structure is large enough.

I'm not really comfortable with making that a blanket assumption. I'd
really like to know exactly what we're overwriting when performing these

You won't be overwriting anything else since you'll be performing an atomic read-modify-write that does not change any of the bits outside the subword of interest. More precisely, you may overwrite those bits outside the subword, but it's guaranteed to be with the current contents so there'll be no externally visible change and you won't clobber anything. Since you'll do an aligned longword operation you can't end up straddling a page boundary or anything nasty like that.

 -- Keir

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