Re: [PATCH v2] tools/mm: prevent page_owner_sort from truncating input

[Andrew Morton]

On Thu, 30 Jul 2026 09:58:09 +0800 Warren Xiong <warren.xiong@xxxxxxxxxx> wrote:

> page_owner_sort opens the output file with "w" before reading the input.
> If both paths refer to the same file, this truncates the input and the
> tool silently processes zero records before returning success.
> 
> Delay opening the output file until all input records have been loaded
> into memory. This allows the tool to sort a file in place without
> truncating data before it has been consumed.

Far nicer, thanks.

However I spotted a thing which Sashiko missed!

> @@ -874,6 +873,13 @@ int main(int argc, char **argv)
>  			goto out_free;
>  	}
>  
> +	fout = fopen(argv[optind + 1], "w");
> +	if (!fout) {
> +		usage();
> +		perror("open: ");
> +		exit(1);
> +	}

usage() calls printf(), which can set errno.  So perror() might print
the wrong thing.

Not that I care very much ;)