bring back close() error checking

Summary:
In stack ending at D66275420, several call sites were migrated from
RawFd with explicit `libc::close()` or `nix::unistd::close()` which
admit the possibility of failure. Now, `close()` failures are
unactionable -- you certainly cannot retry the close operation or risk
closing some other FD -- but it may be worth logging when they happen.

Bring back explicit close operations and error checking.

Reviewed By: jasonwhite

Differential Revision: D67157487

fbshipit-source-id: 254cace779c6f993117fbaaf6e0453df6bdc70e5

reverie-ptrace/Cargo.toml

@@ -13,6 +13,7 @@ anyhow = "1.0.86"
 async-trait = "0.1.71"
 bincode = "1.3.3"
 bytes = { version = "1.6.0", features = ["serde"] }
+close-err = "1.0.2"
 futures = { version = "0.3.30", features = ["async-await", "compat"] }
 goblin = "0.5.2"
 iced-x86 = "1.17.0"

reverie-ptrace/src/tracer.rs

@@ -16,6 +16,7 @@ use std::path::PathBuf;
 use std::sync::Arc;
 
 use anyhow::Context;
+use close_err::Closable;
 use futures::future;
 use futures::future::BoxFuture;
 use futures::future::Either;
@@ -592,13 +593,13 @@ where
     // panicking, etc).  We make a best-effort attempt to solve some of these issues.
     match unsafe { unistd::fork() }.expect("unistd::fork failed") {
         ForkResult::Child => {
-            drop(read1);
-            drop(read2);
+            read1.close()?;
+            read2.close()?;
             if capture_output {
                 unistd::dup2(write1.as_raw_fd(), 1).map_err(from_nix_error)?;
                 unistd::dup2(write2.as_raw_fd(), 2).map_err(from_nix_error)?;
-                drop(write1);
-                drop(write2);
+                write1.close()?;
+                write2.close()?;
             }
 
             init_tracee(events.has_rdtsc()).expect("init_tracee failed");
@@ -625,8 +626,8 @@ where
 
             let guest_pid = Pid::from(child);
             let child = Running::new(guest_pid);
-            drop(write1);
-            drop(write2);
+            write1.close()?;
+            write2.close()?;
 
             let stdout = read1.into();
             let stderr = read2.into();

tests/basics.rs

@@ -17,6 +17,7 @@ use std::os::fd::AsRawFd;
 use std::sync::atomic::AtomicU64;
 use std::sync::atomic::Ordering;
 
+use close_err::Closable;
 #[allow(unused_imports)]
 use nix::sys::wait;
 #[allow(unused_imports)]
@@ -267,7 +268,7 @@ fn child_should_inherit_fds() {
         let msg: [u8; 8] = [0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8];
         match unsafe { unistd::fork() } {
             Ok(ForkResult::Parent { child, .. }) => {
-                drop(fdwrite);
+                fdwrite.close().expect("close failed");
                 let mut buf: [u8; 8] = [0; 8];
                 assert_eq!(unistd::read(fdread.as_raw_fd(), &mut buf), Ok(8));
                 assert_eq!(buf, msg);
@@ -276,7 +277,7 @@ fn child_should_inherit_fds() {
                 unreachable!();
             }
             Ok(ForkResult::Child) => {
-                drop(fdread);
+                fdread.close().expect("close failed");
                 assert_eq!(unistd::write(&fdwrite, &msg), Ok(8));
                 unsafe { libc::syscall(libc::SYS_exit_group, 0) };
                 unreachable!();