Map user buffer only once

This avoids needless page table modifications and also lets us enforce
having writable pages.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index 72d1675..a572ed9 100644
--- a/README.md
+++ b/README.md
@@ -119,6 +119,6 @@ After loading the driver and creating a network interface the typical way using
 ~                              ~
 ```
 
-Each packet segment should contain a layer 3 IPv4 or IPv6 packet. Up to 15728640 bytes may be read or written during each call to `ReadFile` or `WriteFile`.
+Each packet segment should contain a layer 3 IPv4 or IPv6 packet. Up to 15728640 bytes may be read or written during each call to `ReadFile` or `WriteFile`. All calls to `ReadFile` must be called with the same virtual address, and all calls to `WriteFile` must be called with the same virtual address. These virtual addresses must reference pages that are readable and writable for the same length as passed to the first calls of `ReadFile` and `WriteFile`.
 
 It is advisable to use [overlapped I/O](https://docs.microsoft.com/en-us/windows/desktop/sync/synchronization-and-overlapped-input-and-output) for this. If using blocking I/O instead, it may be desirable to open separate handles for reading and writing.