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

[Andrew Morton]

On Wed, 29 Jul 2026 13:38:12 +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.

Don't do that then?  I mean, is there any expectation that this works?

hp2:/usr/src/25> ls -l x
-rw-rw-r-- 1 akpm akpm 55318 Jul 29 17:27 x
hp2:/usr/src/25> sort -o x x
hp2:/usr/src/25> ls -l x    
-rw-rw-r-- 1 akpm akpm 55318 Jul 29 17:27 x

Oh.  sort(1) does that.  I never knew.

> Open the output without truncating it and compare the device and inode
> numbers of the opened files. Reject matching regular files, then truncate
> regular output files only after the check. This also detects hard link and
> symbolic link aliases while preserving non-regular outputs such as
> /dev/stdout.

This all sounds complex.  How does sort(1) do it?  Write to a temporary
file then a rename?

For page_owner_sort I expect we could load all the input into memory
before opening the output file?