Re: [PATCH 0/2] RFC: add -mem-shared option

[Paolo Bonzini]

On 29/11/19 10:39, Daniel P. Berrangé wrote:
> On Fri, Nov 29, 2019 at 10:33:39AM +0100, Paolo Bonzini wrote:
>> On 29/11/19 10:27, Daniel P. Berrangé wrote:
>>>> Yes, with a fallback path currently using a temporary file under /tmp
>>>> (we may want to use shm_open() instead, or a different location such
>>>> as XDG_RUNTIME_DIR? - and use O_TMPFILE)
>>> We can't assume either /tmp or XDG_RUNTIME_DIR is on tmpfs as that is no
>>> where near standard across all OS distros, and even if on tmpfs these
>>> dirs can be size limited to a significant subset of available RAM. IOW
>>> we can't safely use them unless explicitly told to.
>>
>> Agreed, mkstemp+shm_open seems better.  Perhaps this could be done in
>> hostmem-memfd.c though, basically as a fallback option?  In principle
>> one could even use getmntent to search for a hugetlbfs mount.
> 
> With mkstemp you still need to pick a location, and I don't think it
> is clear there is a reliable choice that will always work.

Sorry, I meant mktemp (which is almost never the right choice so my
brain fat-fingered it...) + shm_open(O_CREAT|O_EXCL).

Paolo