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Re: [Xen-devel] [PATCH v2 7/9] xen/gntdev: Implement dma-buf export functionality

On 06/08/2018 01:30 AM, Boris Ostrovsky wrote:
On 06/07/2018 04:44 AM, Oleksandr Andrushchenko wrote:
On 06/07/2018 12:48 AM, Boris Ostrovsky wrote:
On 06/06/2018 08:10 AM, Oleksandr Andrushchenko wrote:
On 06/05/2018 01:07 AM, Boris Ostrovsky wrote:
On 06/01/2018 07:41 AM, Oleksandr Andrushchenko wrote:
+static struct sg_table *
+dmabuf_exp_ops_map_dma_buf(struct dma_buf_attachment *attach,
+               enum dma_data_direction dir)
+    struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach =
+    struct gntdev_dmabuf *gntdev_dmabuf = attach->dmabuf->priv;
+    struct sg_table *sgt;
+    pr_debug("Mapping %d pages for dev %p\n",
+         attach->dev);
+    if (WARN_ON(dir == DMA_NONE || !gntdev_dmabuf_attach))

WARN_ON_ONCE. Here and elsewhere.
Why? The UAPI may be used by different applications, thus we might
lose warnings for some of them. Having WARN_ON will show problems
for multiple users, not for the first one.
Does this make sense to still use WARN_ON?
Just as with pr_err call somewhere else the concern here is that
userland (which I think is where this is eventually called from?) may
intentionally trigger the error, flooding the log.

And even this is not directly called from userland there is still a
possibility of triggering this error multiple times.
Ok, will use WARN_ON_ONCE

In fact, is there a reason to use WARN at all? Does this condition
indicate some sort of internal inconsistency/error?
Well, the corresponding errors are anyways handled, so I will remove WARN

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