[Libguestfs] [PATCH virt-v2v v2 2/2] v2v: Allow large temporary directory to be set on a global basis.

[Pino Toscano]

On Monday, 6 April 2020 11:19:12 CEST Richard W.M. Jones wrote:
> Previously we placed large files in g#get_cachedir () (usually
> /var/tmp).  However the problem is this ties the libguestfs appliance
> and the virt-v2v overlay files to the same location.
> 
> When virt-v2v is run in a container, or any other situation where
> local storage is limited, it's helpful to be able to put the overlay
> files on an externally mounted PVC, which might be using NFS and
> shared between containers.  But putting the libguestfs appliance on
> NFS in a shared location is certainly not recommended.
> 
> This allows the two locations to be set separately:
> 
>   VIRT_V2V_TMPDIR - location of large temporary files, can use NFS
>                     and may be shared
> 
>   LIBGUESTFS_CACHEDIR - location of libguestfs appliance
> 
> Another motivation for this patch is to allow more reliable cleanup of
> large temporary files by an external process, as described in the
> updated documentation.
> 
> Small temporary files are placed in $TMPDIR (usually /tmp).  I cleaned
> up some existing code which used /var/tmp for small temporaries.

(^ this last change reverts 0bc1411fc8693dd981efef0088b3d335a11332cf )

> ---

This is mostly a repost of v1, with even few things that got worse
(I'll mention it later on). Since my requests [1][2] for actual use
cases and motivations behind this went unanswered other than with
- "because containers"
- "because why not"
then, I'll keep NACK-ing this patch.

[1] https://www.redhat.com/archives/libguestfs/2020-April/msg00008.html
[2] https://www.redhat.com/archives/libguestfs/2020-April/msg00010.html

Since the problem is "let's find out what to clean on failure", I
propose a different approach, as also looking at this patch pointed out
to me:
- create a single virt-v2v.XXXXXX temporary directory in
  LIBGUESTFS_TMPDIR for small files, like the vmx file, the rhv-upload
  Python scripts, etc
- create a single virt-v2v.XXXXXX temporary directory in
  LIBGUESTFS_CACHEDIR for big files
Advantages:
- no more need for the various Mkdtemp.temp_dir all around
- only two well-defined names for temporary stuff that virt-v2v saves
- similar to what done in other tools (eg virt-builder, 75fbe4511e05df)

I'll send a patch for this shortly.

-- 
Pino Toscano
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