add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/mm/frame_vector.c
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@@ -29,6 +29,10 @@
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  * different type underlying the specified range of virtual addresses.
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  * When the function isn't able to map a single page, it returns error.
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  *
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+ * Note that get_vaddr_frames() cannot follow VM_IO mappings. It used
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+ * to be able to do that, but that could (racily) return non-refcounted
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+ * pfns.
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+ *
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  * This function takes care of grabbing mmap_lock as necessary.
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  */
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 int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
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@@ -77,8 +81,6 @@
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 			goto out;
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 	}
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-	/* This used to (racily) return non-refcounted pfns. Let people know */
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-	WARN_ONCE(1, "get_vaddr_frames() cannot follow VM_IO mapping");
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 	vec->nr_frames = 0;
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 out: