[RFC PATCH 03/24] erofs: add Errno in Rust

[Yiyang Wu <toolmanp@tlmp.cc>]

Introduce Errno to Rust side code. Note that in current Rust For Linux,
Errnos are implemented as core::ffi::c_uint unit structs.
However, EUCLEAN, a.k.a EFSCORRUPTED is missing from error crate.

Since the errno_base hasn't changed for over 13 years,
This patch merely serves as a temporary workaround for the missing
errno in the Rust For Linux.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
 fs/erofs/rust/erofs_sys.rs        |   6 +
 fs/erofs/rust/erofs_sys/errnos.rs | 191 ++++++++++++++++++++++++++++++
 2 files changed, 197 insertions(+)
 create mode 100644 fs/erofs/rust/erofs_sys/errnos.rs

diff --git a/fs/erofs/rust/erofs_sys.rs b/fs/erofs/rust/erofs_sys.rs
index 0f1400175fc2..2bd1381da5ab 100644
--- a/fs/erofs/rust/erofs_sys.rs
+++ b/fs/erofs/rust/erofs_sys.rs
@@ -19,4 +19,10 @@
 pub(crate) type Nid = u64;
 /// Erofs Super Offset to read the ondisk superblock
 pub(crate) const EROFS_SUPER_OFFSET: Off = 1024;
+/// PosixResult as a type alias to kernel::error::Result
+/// to avoid naming conflicts.
+pub(crate) type PosixResult<T> = Result<T, Errno>;
+
+pub(crate) mod errnos;
 pub(crate) mod superblock;
+pub(crate) use errnos::Errno;
diff --git a/fs/erofs/rust/erofs_sys/errnos.rs b/fs/erofs/rust/erofs_sys/errnos.rs
new file mode 100644
index 000000000000..40e5cdbcb353
--- /dev/null
+++ b/fs/erofs/rust/erofs_sys/errnos.rs
@@ -0,0 +1,191 @@
+// Copyright 2024 Yiyang Wu
+// SPDX-License-Identifier: MIT or GPL-2.0-or-later
+
+#[repr(i32)]
+#[non_exhaustive]
+#[allow(clippy::upper_case_acronyms)]
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub(crate) enum Errno {
+    NONE = 0,
+    EPERM,
+    ENOENT,
+    ESRCH,
+    EINTR,
+    EIO,
+    ENXIO,
+    E2BIG,
+    ENOEXEC,
+    EBADF,
+    ECHILD,
+    EAGAIN,
+    ENOMEM,
+    EACCES,
+    EFAULT,
+    ENOTBLK,
+    EBUSY,
+    EEXIST,
+    EXDEV,
+    ENODEV,
+    ENOTDIR,
+    EISDIR,
+    EINVAL,
+    ENFILE,
+    EMFILE,
+    ENOTTY,
+    ETXTBSY,
+    EFBIG,
+    ENOSPC,
+    ESPIPE,
+    EROFS,
+    EMLINK,
+    EPIPE,
+    EDOM,
+    ERANGE,
+    EDEADLK,
+    ENAMETOOLONG,
+    ENOLCK,
+    ENOSYS,
+    ENOTEMPTY,
+    ELOOP,
+    ENOMSG = 42,
+    EIDRM,
+    ECHRNG,
+    EL2NSYNC,
+    EL3HLT,
+    EL3RST,
+    ELNRNG,
+    EUNATCH,
+    ENOCSI,
+    EL2HLT,
+    EBADE,
+    EBADR,
+    EXFULL,
+    ENOANO,
+    EBADRQC,
+    EBADSLT,
+    EBFONT = 59,
+    ENOSTR,
+    ENODATA,
+    ETIME,
+    ENOSR,
+    ENONET,
+    ENOPKG,
+    EREMOTE,
+    ENOLINK,
+    EADV,
+    ESRMNT,
+    ECOMM,
+    EPROTO,
+    EMULTIHOP,
+    EDOTDOT,
+    EBADMSG,
+    EOVERFLOW,
+    ENOTUNIQ,
+    EBADFD,
+    EREMCHG,
+    ELIBACC,
+    ELIBBAD,
+    ELIBSCN,
+    ELIBMAX,
+    ELIBEXEC,
+    EILSEQ,
+    ERESTART,
+    ESTRPIPE,
+    EUSERS,
+    ENOTSOCK,
+    EDESTADDRREQ,
+    EMSGSIZE,
+    EPROTOTYPE,
+    ENOPROTOOPT,
+    EPROTONOSUPPORT,
+    ESOCKTNOSUPPORT,
+    EOPNOTSUPP,
+    EPFNOSUPPORT,
+    EAFNOSUPPORT,
+    EADDRINUSE,
+    EADDRNOTAVAIL,
+    ENETDOWN,
+    ENETUNREACH,
+    ENETRESET,
+    ECONNABORTED,
+    ECONNRESET,
+    ENOBUFS,
+    EISCONN,
+    ENOTCONN,
+    ESHUTDOWN,
+    ETOOMANYREFS,
+    ETIMEDOUT,
+    ECONNREFUSED,
+    EHOSTDOWN,
+    EHOSTUNREACH,
+    EALREADY,
+    EINPROGRESS,
+    ESTALE,
+    EUCLEAN,
+    ENOTNAM,
+    ENAVAIL,
+    EISNAM,
+    EREMOTEIO,
+    EDQUOT,
+    ENOMEDIUM,
+    EMEDIUMTYPE,
+    ECANCELED,
+    ENOKEY,
+    EKEYEXPIRED,
+    EKEYREVOKED,
+    EKEYREJECTED,
+    EOWNERDEAD,
+    ENOTRECOVERABLE,
+    ERFKILL,
+    EHWPOISON,
+    EUNKNOWN,
+}
+
+impl From<i32> for Errno {
+    fn from(value: i32) -> Self {
+        if (-value) <= 0 || (-value) > Errno::EUNKNOWN as i32 {
+            Errno::EUNKNOWN
+        } else {
+            // Safety: The value is guaranteed to be a valid errno and the memory
+            // layout is the same for both types.
+            unsafe { core::mem::transmute(value) }
+        }
+    }
+}
+
+impl From<Errno> for i32 {
+    fn from(value: Errno) -> Self {
+        -(value as i32)
+    }
+}
+
+/// Replacement for ERR_PTR in Linux Kernel.
+impl From<Errno> for *const core::ffi::c_void {
+    fn from(value: Errno) -> Self {
+        (-(value as core::ffi::c_long)) as *const core::ffi::c_void
+    }
+}
+
+impl From<Errno> for *mut core::ffi::c_void {
+    fn from(value: Errno) -> Self {
+        (-(value as core::ffi::c_long)) as *mut core::ffi::c_void
+    }
+}
+
+/// Replacement for PTR_ERR in Linux Kernel.
+impl From<*const core::ffi::c_void> for Errno {
+    fn from(value: *const core::ffi::c_void) -> Self {
+        (-(value as i32)).into()
+    }
+}
+
+impl From<*mut core::ffi::c_void> for Errno {
+    fn from(value: *mut core::ffi::c_void) -> Self {
+        (-(value as i32)).into()
+    }
+}
+/// Replacement for IS_ERR in Linux Kernel.
+#[inline(always)]
+pub(crate) fn is_value_err(value: *const core::ffi::c_void) -> bool {
+    (value as core::ffi::c_ulong) >= (-4095 as core::ffi::c_long) as core::ffi::c_ulong
+}
-- 
2.46.0