unexpeced errno 5 in Io.Threaded.dirOpenDirPosix #35185

Mcrtin commented 2026年05月03日 18:33:12 +02:00

Zig Version

0.16.0

Steps to Reproduce and Observed Behavior

I forgot to unmount a usbstick and when trying to walk '/' to produce the dir size, i got this error:

unexpected errno: 5
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/posix.zig:1672:40: 0x1029c90 in unexpectedErrno (std.zig)
 std.debug.dumpCurrentStackTrace(.{});
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:1446:37: 0x112ce18 in unexpectedErrno (std.zig)
 return posix.unexpectedErrno(err);
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:5301:57: 0x118ae59 in dirOpenDirPosix (std.zig)
 else => |err| return syscall.unexpectedErrno(err),
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:482:32: 0x119127a in openDir (std.zig)
 return io.vtable.dirOpenDir(io.userdata, dir, sub_path, options);
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:284:40: 0x11d21bb in enter (std.zig)
 var new_dir = entry.dir.openDir(io, entry.basename, .{ .iterate = true }) catch |err| {
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:368:33: 0x11d26e4 in next (std.zig)
 try self.inner.enter(io, entry.?);
 ^
/home/martin/Documents/dug/src/main.zig:25:31: 0x11d2c4e in main (main.zig)
 var next = walker.next(io);
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:737:30: 0x11d3dae in callMain (std.zig)
 return wrapMain(root.main(.{
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:190:5: 0x11d20e1 in _start (std.zig)
 asm volatile (switch (native_arch) {
 ^
unexpected errno: 5
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/posix.zig:1672:40: 0x1029c90 in unexpectedErrno (std.zig)
 std.debug.dumpCurrentStackTrace(.{});
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:1446:37: 0x112ce18 in unexpectedErrno (std.zig)
 return posix.unexpectedErrno(err);
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:5301:57: 0x118ae59 in dirOpenDirPosix (std.zig)
 else => |err| return syscall.unexpectedErrno(err),
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:482:32: 0x119127a in openDir (std.zig)
 return io.vtable.dirOpenDir(io.userdata, dir, sub_path, options);
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:284:40: 0x11d21bb in enter (std.zig)
 var new_dir = entry.dir.openDir(io, entry.basename, .{ .iterate = true }) catch |err| {
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:368:33: 0x11d26e4 in next (std.zig)
 try self.inner.enter(io, entry.?);
 ^
/home/martin/Documents/dug/src/main.zig:27:28: 0x11d2cb3 in main (main.zig)
 if (walker.next(io)) |res| break :blk res else |err| switch (err) {
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:737:30: 0x11d3dae in callMain (std.zig)
 return wrapMain(root.main(.{
 ^
/nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:190:5: 0x11d20e1 in _start (std.zig)
 asm volatile (switch (native_arch) {
 ^

digging a bit you can see that the IO linux error isn't handled here:

constrc=openat_sym(dir.handle,sub_path_posix,flags,mode);switch(posix.errno(rc)){.SUCCESS=>{syscall.finish();return.{.handle=@intCast(rc)};},.INTR=>{trysyscall.checkCancel();continue;},.INVAL=>returnsyscall.fail(error.BadPathName),.ACCES=>returnsyscall.fail(error.AccessDenied),.LOOP=>returnsyscall.fail(error.SymLinkLoop),.MFILE=>returnsyscall.fail(error.ProcessFdQuotaExceeded),.NAMETOOLONG=>returnsyscall.fail(error.NameTooLong),.NFILE=>returnsyscall.fail(error.SystemFdQuotaExceeded),.NODEV=>returnsyscall.fail(error.NoDevice),.NOENT=>returnsyscall.fail(error.FileNotFound),.NOMEM=>returnsyscall.fail(error.SystemResources),.NOTDIR=>returnsyscall.fail(error.NotDir),.PERM=>returnsyscall.fail(error.PermissionDenied),.NXIO=>returnsyscall.fail(error.NoDevice),.ILSEQ=>returnsyscall.fail(error.BadPathName),.FAULT=>|err|returnsyscall.errnoBug(err),.BADF=>|err|returnsyscall.errnoBug(err),// File descriptor used after closed..BUSY=>|err|returnsyscall.errnoBug(err),// O_EXCL not passedelse=>|err|returnsyscall.unexpectedErrno(err),

Expected Behavior

I would expect the IO error to be expected here.

### Zig Version 0.16.0 ### Steps to Reproduce and Observed Behavior I forgot to unmount a usbstick and when trying to walk '/' to produce the dir size, i got this error: ``` unexpected errno: 5 /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/posix.zig:1672:40: 0x1029c90 in unexpectedErrno (std.zig) std.debug.dumpCurrentStackTrace(.{}); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:1446:37: 0x112ce18 in unexpectedErrno (std.zig) return posix.unexpectedErrno(err); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:5301:57: 0x118ae59 in dirOpenDirPosix (std.zig) else => |err| return syscall.unexpectedErrno(err), ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:482:32: 0x119127a in openDir (std.zig) return io.vtable.dirOpenDir(io.userdata, dir, sub_path, options); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:284:40: 0x11d21bb in enter (std.zig) var new_dir = entry.dir.openDir(io, entry.basename, .{ .iterate = true }) catch |err| { ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:368:33: 0x11d26e4 in next (std.zig) try self.inner.enter(io, entry.?); ^ /home/martin/Documents/dug/src/main.zig:25:31: 0x11d2c4e in main (main.zig) var next = walker.next(io); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:737:30: 0x11d3dae in callMain (std.zig) return wrapMain(root.main(.{ ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:190:5: 0x11d20e1 in _start (std.zig) asm volatile (switch (native_arch) { ^ unexpected errno: 5 /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/posix.zig:1672:40: 0x1029c90 in unexpectedErrno (std.zig) std.debug.dumpCurrentStackTrace(.{}); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:1446:37: 0x112ce18 in unexpectedErrno (std.zig) return posix.unexpectedErrno(err); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Threaded.zig:5301:57: 0x118ae59 in dirOpenDirPosix (std.zig) else => |err| return syscall.unexpectedErrno(err), ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:482:32: 0x119127a in openDir (std.zig) return io.vtable.dirOpenDir(io.userdata, dir, sub_path, options); ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:284:40: 0x11d21bb in enter (std.zig) var new_dir = entry.dir.openDir(io, entry.basename, .{ .iterate = true }) catch |err| { ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/Io/Dir.zig:368:33: 0x11d26e4 in next (std.zig) try self.inner.enter(io, entry.?); ^ /home/martin/Documents/dug/src/main.zig:27:28: 0x11d2cb3 in main (main.zig) if (walker.next(io)) |res| break :blk res else |err| switch (err) { ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:737:30: 0x11d3dae in callMain (std.zig) return wrapMain(root.main(.{ ^ /nix/store/5x5y75rc3l43ic0lwal6wzk7wi1ga3m1-zig-0.16.0/lib/zig/std/start.zig:190:5: 0x11d20e1 in _start (std.zig) asm volatile (switch (native_arch) { ^ ``` digging a bit you can see that the `IO` linux error isn't handled here: ```zig const rc = openat_sym(dir.handle, sub_path_posix, flags, mode); switch (posix.errno(rc)) { .SUCCESS => { syscall.finish(); return .{ .handle = @intCast(rc) }; }, .INTR => { try syscall.checkCancel(); continue; }, .INVAL => return syscall.fail(error.BadPathName), .ACCES => return syscall.fail(error.AccessDenied), .LOOP => return syscall.fail(error.SymLinkLoop), .MFILE => return syscall.fail(error.ProcessFdQuotaExceeded), .NAMETOOLONG => return syscall.fail(error.NameTooLong), .NFILE => return syscall.fail(error.SystemFdQuotaExceeded), .NODEV => return syscall.fail(error.NoDevice), .NOENT => return syscall.fail(error.FileNotFound), .NOMEM => return syscall.fail(error.SystemResources), .NOTDIR => return syscall.fail(error.NotDir), .PERM => return syscall.fail(error.PermissionDenied), .NXIO => return syscall.fail(error.NoDevice), .ILSEQ => return syscall.fail(error.BadPathName), .FAULT => |err| return syscall.errnoBug(err), .BADF => |err| return syscall.errnoBug(err), // File descriptor used after closed. .BUSY => |err| return syscall.errnoBug(err), // O_EXCL not passed else => |err| return syscall.unexpectedErrno(err), ``` ### Expected Behavior I would expect the `IO` error to be expected here.

mewssix commented 2026年05月06日 07:53:29 +02:00

I'll check this out. Is there any sort of sample program for reproducing of this issue?

I'll check this out. Is there any sort of sample program for reproducing of this issue?

Mcrtin commented 2026年05月06日 09:31:10 +02:00

I was walking / (root) and forgot to unmount a device I already disconnected

I was walking `/` (root) and forgot to unmount a device I already disconnected

yarnf commented 2026年05月15日 19:28:45 +02:00

https://mail-archive.com/ubuntu-bugs@lists.ubuntu.com/msg2424693.html

Seems that EIO can be returned from a number of calls such as open, openat (which is the method in question for dirOpenDirPosix - well that or openat64 ofc) despite not being listen on their man pages (on my system at least). Its just propogated from the underlying block device or the like (I guess). I'm not sure if theres other places this should be handled.

Its listed here, although the description doesn't really match with this case (if @Mcrtin did in fact get EIO). That or I'm confused which is always a possiblity :)
https://www.ibm.com/docs/en/zos/3.2.0?topic=functions-openat-open-file-relative-directory-file-descriptor

EIO The pathname argument names a STREAMS file and a hang-up or error occurred during the open().

https://mail-archive.com/ubuntu-bugs@lists.ubuntu.com/msg2424693.html Seems that EIO can be returned from a number of calls such as `open`, `openat` (which is the method in question for `dirOpenDirPosix` - well that or `openat64` ofc) despite not being listen on their man pages (on my system at least). Its just propogated from the underlying block device or the like (I guess). I'm not sure if theres other places this should be handled. Its listed here, although the description doesn't really match with this case (if @Mcrtin did in fact get EIO). That or I'm confused which is always a possiblity :) https://www.ibm.com/docs/en/zos/3.2.0?topic=functions-openat-open-file-relative-directory-file-descriptor `EIO The pathname argument names a STREAMS file and a hang-up or error occurred during the open().`