Emulate flock() on Solaris via fcntl().

This should resolve problem with Rust build:
rust-lang/rust#103630

Author: psumbera

src/backend/libc/fs/syscalls.rs

@@ -86,7 +86,7 @@ use crate::fs::Advice;
     target_os = "solaris",
 )))]
 use crate::fs::FallocateFlags;
-#[cfg(not(any(target_os = "solaris", target_os = "wasi")))]
+#[cfg(not(target_os = "wasi"))]
 use crate::fs::FlockOperation;
 #[cfg(any(target_os = "android", target_os = "freebsd", target_os = "linux"))]
 use crate::fs::MemfdFlags;
@@ -968,6 +968,37 @@ pub(crate) fn flock(fd: BorrowedFd<'_>, operation: FlockOperation) -> io::Result
     unsafe { ret(c::flock(borrowed_fd(fd), operation as c::c_int)) }
 }
 
+#[cfg(target_os = "solaris")]
+pub(crate) fn flock(fd: BorrowedFd<'_>, operation: FlockOperation) -> io::Result<()> {
+    // Solaris lacks flock(), so try to emulate using fcntl()
+    let flag = operation as c::c_int;
+    let mut flock = c::flock {
+        l_type: 0,
+        l_whence: 0,
+        l_start: 0,
+        l_len: 0,
+        l_sysid: 0,
+        l_pid: 0,
+        l_pad: [0, 0, 0, 0],
+    };
+    flock.l_type = if flag & libc::LOCK_UN != 0 {
+         libc::F_UNLCK
+    } else if flag & libc::LOCK_EX != 0 {
+         libc::F_WRLCK
+    } else if flag & libc::LOCK_SH != 0 {
+         libc::F_RDLCK
+    } else {
+         panic!("unexpected flock() operation")
+    };
+
+    let mut cmd = libc::F_SETLKW;
+    if (flag & libc::LOCK_NB) != 0 {
+         cmd = libc::F_SETLK;
+    }
+
+    unsafe { ret(c::fcntl(borrowed_fd(fd), cmd, &flock)) }
+}
+
 pub(crate) fn fstat(fd: BorrowedFd<'_>) -> io::Result<Stat> {
     // 32-bit and mips64 Linux: `struct stat64` is not y2038 compatible; use
     // `statx`.

src/backend/libc/fs/types.rs

@@ -850,7 +850,7 @@ bitflags! {
 /// `LOCK_*` constants for use with [`flock`]
 ///
 /// [`flock`]: crate::fs::flock
-#[cfg(not(any(target_os = "solaris", target_os = "wasi")))]
+#[cfg(not(target_os = "wasi"))]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 #[repr(i32)]
 pub enum FlockOperation {

src/fs/fd.rs

@@ -8,7 +8,7 @@ use crate::process::{Gid, Uid};
 use crate::{backend, io};
 use backend::fd::{AsFd, BorrowedFd};
 
-#[cfg(not(any(target_os = "solaris", target_os = "wasi")))]
+#[cfg(not(target_os = "wasi"))]
 pub use backend::fs::types::FlockOperation;
 
 #[cfg(not(any(
@@ -343,7 +343,7 @@ pub fn ftruncate<Fd: AsFd>(fd: Fd, length: u64) -> io::Result<()> {
 ///  - [Linux]
 ///
 /// [Linux]: https://man7.org/linux/man-pages/man2/flock.2.html
-#[cfg(not(any(target_os = "solaris", target_os = "wasi")))]
+#[cfg(not(target_os = "wasi"))]
 #[inline]
 pub fn flock<Fd: AsFd>(fd: Fd, operation: FlockOperation) -> io::Result<()> {
     backend::fs::syscalls::flock(fd.as_fd(), operation)

src/fs/mod.rs

@@ -162,7 +162,7 @@ pub use fd::fdatasync;
 pub use fd::{fallocate, FallocateFlags};
 #[cfg(not(target_os = "wasi"))]
 pub use fd::{fchmod, fchown};
-#[cfg(not(any(target_os = "solaris", target_os = "wasi")))]
+#[cfg(not(target_os = "wasi"))]
 pub use fd::{flock, FlockOperation};
 pub use fd::{fstat, fsync, ftruncate, futimens, is_file_read_write, seek, tell, Stat, Timestamps};
 #[cfg(not(any(