Re: [PATCH] block: honor $TMPDIR in create_tmp_file()

[Richard Henderson <richard.henderson@linaro.org>]

On 9/1/25 15:31, Michael Tokarev wrote:
> On 01.09.2025 01:39, Richard Henderson wrote:
>> On 8/31/25 21:48, Michael Tokarev wrote:
>>>       /*
>>>        * See commit 69bef79 ("block: use /var/tmp instead of /tmp for -snapshot")
>>>        *
>>> @@ -862,7 +860,12 @@ char *create_tmp_file(Error **errp)
>>>        * so the files can become very large. /tmp is often a tmpfs where as
>>>        * /var/tmp is usually on a disk, so more appropriate for disk images.
>>>        */
>>
>> This is going to cause other failures, per the tmpfs reason given in the comment.
> 
> This is the comment:
> 
>       * This function is used to create temporary disk images (like -snapshot),
>       * so the files can become very large. /tmp is often a tmpfs where as
>       * /var/tmp is usually on a disk, so more appropriate for disk images.
> 
> It does not give reasons for "other failures".

It does gloss over the implications of "tmpfs".  But off the top of my head:

(1) tmpfs is generally smaller than any other disk-based tmpdir,
     so ENOSPC is easier to trigger, and
(2) tmpfs does not support several O_FOO.

> 
> Are you saying the user, who decided to explicitly specify TMPDIR,
> is wrong, and qemu should use /var/tmp which does not even exist
> (see the bug report this patch is fixing)?

I think this is a very strong interpretation since the non-existence of /var/tmp is, IMO, 
new and rare.  /var/tmp most certainly *does* exist with all of the major distros.


> The original code (before 69fbfff95e84) was correct.  Current code
> is not.  My change fixes current wrong code.

If this goes in as-is, you are on the hook for any reported testsuite regression.


r~