bug#29961: [PATCH] mv -n: do not overwrite the destination

[Paul Eggert]

Kamil Dudka wrote:
> -      if (rename (src_name, dst_name) == 0)
> +      int flags = 0;
> +      if (x->interactive == I_ALWAYS_NO)
> +        /* do not replace DST_NAME if it was created since our last check */
> +        flags = RENAME_NOREPLACE;

By then it's too late, as multiple decisions have been made on the basis of 
stat/lstat calls that are still subject to races. It's better to try the 
renameat2 with RENAME_NOREPLACE first thing, and fall back on the existing code 
only if renameat2 fails with errno != EEXIST.

Plus, there are some other problems when combining -u and -n.

How about the attached patch instead?

0001-mv-improve-n-atomicity.patch
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