add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/include/xen/grant_table.h
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@@ -97,16 +97,31 @@
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  * access has been ended, free the given page too.  Access will be ended
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  * immediately iff the grant entry is not in use, otherwise it will happen
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  * some time later.  page may be 0, in which case no freeing will occur.
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+ * Note that the granted page might still be accessed (read or write) by the
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+ * other side after gnttab_end_foreign_access() returns, so even if page was
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+ * specified as 0 it is not allowed to just reuse the page for other
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+ * purposes immediately. gnttab_end_foreign_access() will take an additional
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+ * reference to the granted page in this case, which is dropped only after
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+ * the grant is no longer in use.
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+ * This requires that multi page allocations for areas subject to
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+ * gnttab_end_foreign_access() are done via alloc_pages_exact() (and freeing
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+ * via free_pages_exact()) in order to avoid high order pages.
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  */
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 void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
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 			       unsigned long page);
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+
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+/*
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+ * End access through the given grant reference, iff the grant entry is
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+ * no longer in use.  In case of success ending foreign access, the
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+ * grant reference is deallocated.
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+ * Return 1 if the grant entry was freed, 0 if it is still in use.
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+ */
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+int gnttab_try_end_foreign_access(grant_ref_t ref);
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 int gnttab_grant_foreign_transfer(domid_t domid, unsigned long pfn);
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 unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref);
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 unsigned long gnttab_end_foreign_transfer(grant_ref_t ref);
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-
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-int gnttab_query_foreign_access(grant_ref_t ref);
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 /*
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  * operations on reserved batches of grant references
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@@ -199,6 +214,23 @@
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 int gnttab_alloc_pages(int nr_pages, struct page **pages);
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 void gnttab_free_pages(int nr_pages, struct page **pages);
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+struct gnttab_page_cache {
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+	spinlock_t		lock;
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+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
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+	struct page		*pages;
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+#else
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+	struct list_head	pages;
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+#endif
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+	unsigned int		num_pages;
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+};
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+
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+void gnttab_page_cache_init(struct gnttab_page_cache *cache);
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+int gnttab_page_cache_get(struct gnttab_page_cache *cache, struct page **page);
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+void gnttab_page_cache_put(struct gnttab_page_cache *cache, struct page **page,
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+			   unsigned int num);
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+void gnttab_page_cache_shrink(struct gnttab_page_cache *cache,
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+			      unsigned int num);
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+
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 #ifdef CONFIG_XEN_GRANT_DMA_ALLOC
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 struct gnttab_dma_alloc_args {
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 	/* Device for which DMA memory will be/was allocated. */