base: remove use of cvt crate

cvt isn't used anywhere else in the base crate, and it isn't included in
the ChromeOS crosvm ebuild, so this breaks the CrOS build. Just check
the result and return an error the same way we do elsewhere in base.

BUG=b:231641496
TEST=cargo build
TEST=emerge-hatch crosvm

Fixes: 21445b1b83 ("base: Upstream unix net set_nonblocking fn")
Change-Id: Iba8beee21810210e50e0c715a1b84de29278625a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3716851
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Dennis Kempin <denniskempin@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

base/Cargo.toml

@@ -27,9 +27,6 @@ tempfile = "3"
 thiserror = "1.0.20"
 uuid = { version = "0.8.2", features = ["v4"] }
 
-[target.'cfg(unix)'.dependencies]
-cvt = "*"
-
 [target.'cfg(windows)'.dependencies]
 lazy_static = "*"
 rand = "*"

base/src/sys/unix/net.rs

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-use cvt::cvt;
 use std::{
     cmp::Ordering,
     convert::TryFrom,
@@ -599,7 +598,12 @@ impl UnixSeqpacket {
     /// Sets the blocking mode for this socket.
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;
-        cvt(unsafe { libc::ioctl(self.fd, libc::FIONBIO, &mut nonblocking) }).map(drop)
+        let ret = unsafe { libc::ioctl(self.fd, libc::FIONBIO, &mut nonblocking) };
+        if ret < 0 {
+            Err(io::Error::last_os_error())
+        } else {
+            Ok(())
+        }
     }
 }
 
@@ -798,7 +802,12 @@ impl UnixSeqpacketListener {
     /// Sets the blocking mode for this socket.
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;
-        cvt(unsafe { libc::ioctl(self.fd, libc::FIONBIO, &mut nonblocking) }).map(drop)
+        let ret = unsafe { libc::ioctl(self.fd, libc::FIONBIO, &mut nonblocking) };
+        if ret < 0 {
+            Err(io::Error::last_os_error())
+        } else {
+            Ok(())
+        }
     }
 }