From 47c5f556c08c1b15c74dbaca743d17a3297bcdef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Igor=20Anic=CC=81?= <igor.anic@gmail.com>
Date: Sat, 1 Aug 2026 13:41:45 +0200
Subject: [PATCH] Io.Uring: fix dir.hardLink

Unsupported flags is used resulting in invalid arguments:
```Zig
thread 556130 panic: programmer bug caused syscall error: INVAL
.../lib/std/Io/Threaded.zig:14258:34: 0x116f3fa in errnoBug (std.zig)
    if (is_debug) std.debug.panic("programmer bug caused syscall error: {t}", .{err});
                                 ^
.../lib/std/Io/Uring.zig:5583:44: 0x1281981 in linkat (std.zig)
            .INVAL => |err| return errnoBug(err),
                                           ^
.../lib/std/Io/Uring.zig:3555:21: 0x1289ab9 in dirHardLink (std.zig)
    return ev.linkat(```
```

```Zig
test "linkat" {
    const gpa = testing.allocator;

    var uring: Io.Uring = undefined;
    try uring.init(gpa, .{});
    defer uring.deinit();

    var threaded = Io.Threaded.init(gpa, .{});
    defer threaded.deinit();

    for ([_]Io{ threaded.io(), uring.io() }) |io| {
        var tmp = testing.tmpDir(.{});
        defer tmp.cleanup();
        const dir = tmp.dir;

        const dir2 = try dir.createDirPathOpen(io, "folder/sub_folder", .{});
        defer dir2.close(io);

        const file = try dir.createFile(io, "file", .{});
        defer file.close(io);
        try dir.hardLink("file", dir2, "link", io, .{});
        try file.hardLink(io, dir2, "link2", .{});

        var stat = try dir.statFile(io, "folder/sub_folder/link", .{});
        try testing.expectEqual(.file, stat.kind);
        stat = try dir.statFile(io, "folder/sub_folder/link2", .{});
        try testing.expectEqual(.file, stat.kind);
    }
}
```
---
 lib/std/Io/Uring.zig | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/std/Io/Uring.zig b/lib/std/Io/Uring.zig
index 58d97dc0e8e090c84bec204f74be93a8bd5e5c37..6edf381378148e64941e64559150f77ad94a0650 100644
--- a/lib/std/Io/Uring.zig
+++ b/lib/std/Io/Uring.zig
@@ -3561,7 +3561,7 @@ fn dirHardLink(
         old_sub_path_posix,
         new_dir.handle,
         new_sub_path_posix,
-        if (options.follow_symlinks) 0 else linux.AT.SYMLINK_NOFOLLOW,
+        if (options.follow_symlinks) linux.AT.SYMLINK_FOLLOW else 0,
     );
 }
 
@@ -3993,7 +3993,7 @@ fn fileHardLink(
         "",
         new_dir.handle,
         new_sub_path_posix,
-        linux.AT.EMPTY_PATH | @as(u32, if (options.follow_symlinks) 0 else linux.AT.SYMLINK_NOFOLLOW),
+        linux.AT.EMPTY_PATH | @as(u32, if (options.follow_symlinks) linux.AT.SYMLINK_FOLLOW else 0),
     );
 }
 
@@ -5545,6 +5545,8 @@ fn linkat(
     new_path: [*:0]const u8,
     flags: u32,
 ) File.HardLinkError!void {
+    // allowed flags: https://man7.org/linux/man-pages/man2/linkat.2.html
+    assert(flags & ~(@as(u32, linux.AT.SYMLINK_FOLLOW | linux.AT.EMPTY_PATH)) == 0);
     while (true) {
         const thread = try cancel_region.awaitIoUring();
         thread.enqueue().* = .{
-- 
2.54.0