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Re: [Xen-devel] [patch 6/6] netif_release_rx_bufs

To: Gerd Hoffmann <kraxel@xxxxxxx>
Subject: Re: [Xen-devel] [patch 6/6] netif_release_rx_bufs
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 17 Aug 2006 16:54:55 +0100
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On 17/8/06 4:13 pm, "Gerd Hoffmann" <kraxel@xxxxxxx> wrote:

>>> I think we need either a way to get back pages with transfer grants
>>> without cooperation from the backend driver, or we need some way to say
>>> "pretty pretty please, give me back my rx buffers" to the netback driver.
>> Unlike a map grant, you can reclaim a transfer grant at any time. The only
>> question is whether it has been used to transfer a page, or not.
> How can I do that?  gnttab_end_foreign_transfer_ref() doesn't cut it, it
> will not succeed unconditionally ...

The function will not spin unboundedly and, when it returns, the grant is
definitely no longer active. If any page was transferred via the grant, it
is returned to the caller (else zero is returned). It does just what you

 -- Keir

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