Re: [PATCH v11 0/4] MR6855: server: Fix renaming file to a hardlink of itself.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about server/fd.c:
> +    if (!is_dir)
> +    {
> +        /* we can't just do rename(2) here; renaming a file to its hardlink is no-op */
> +        if (linkat( dirfd, tmpname, dirfd, dstname, 0 ) && errno != EEXIST)
> +        {
> +            if (errno == EPERM || errno == EOPNOTSUPP)
> +            {
> +                /* FIXME: filesystem doesn't support hardlinks, entire operation might be a no-op on casefold dirs */
> +                if (renameat( dirfd, tmpname, dirfd, dstname ))
> +                    file_set_error();
> +                goto ret;
> +            }
> +
> +            file_set_error();
> +            /* revert the temporary rename */
> +            renameat( dirfd, tmpname, dirfd, srcname );
> Let's make this a common logic for all cases (hardlink, no hardlink, & dir).

Something like this (untested):

```c
    int undo_tmp_rename = 0;

    (...)

    undo_tmp_rename = 1;

    /* directories can't have hardlinks */
    if (!is_dir)
    {
        /* we can't just do rename(2) here; renaming a file to its hardlink is no-op */
        if (linkat( dirfd, tmpname, dirfd, dstname, 0 ) && errno != EEXIST)
        {
            if (errno != EPERM && errno != EOPNOTSUPP)
            {
                file_set_error();
                goto ret;
            }

            /* Filesystem doesn't support hardlinks, fall back to renaming */
        }
        else
        {
            undo_tmp_rename = 0;

            if (unlinkat( dirfd, tmpname, 0 ))
                file_set_error();

            goto ret;  /* We're done */
        }
    }

    /* Renaming a directory, or filesystem doesn't support hardlinks */
    if (renameat( dirfd, tmpname, dirfd, dstname ))
        file_set_error();
    else
        undo_tmp_rename = 0;

ret:
    if (undo_tmp_rename)
    {
        /* revert the temporary rename */
        renameat( dirfd, tmpname, dirfd, srcname );
    }
```

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/6855#note_98191