vhost: Fix building docs

Building docs (as on docs.rs) has been broken since 8ee8739. This commit
introduces POSTCOPY and made this feature mutually exclusive with xen.

As docs are build for all features the corresponding check will be
triggered and the docs can not be built.

This patch extends the check to allow both "postcopy" and "xen" to be
enabled when building docs.

Signed-off-by: Christian Speich <[email protected]>

Author: kleinweby

vhost/CHANGELOG.md

@@ -6,6 +6,7 @@
 ### Changed
 ### Deprecated
 ### Fixed
+- [[#304]](https://github.com/rust-vmm/vhost/pull/304) Fix building docs.
 
 ## v0.14.0
 

vhost/src/lib.rs

@@ -54,7 +54,7 @@ pub mod vsock;
 /// Due to the way `xen` handles memory mappings we can not combine it with
 /// `postcopy` feature which relies on persistent memory mappings. Thus we
 /// disallow enabling both features at the same time.
-#[cfg(all(feature = "postcopy", feature = "xen"))]
+#[cfg(all(not(doc), feature = "postcopy", feature = "xen"))]
 compile_error!("Both `postcopy` and `xen` features can not be enabled at the same time.");
 
 /// Error codes for vhost operations