Re: [Libguestfs] [PATCH virt-v2v] v2v: Allow temporary directory to be set on a global basis.

On Thursday, 2 April 2020 14:49:18 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 > temporary files by an external process, as described in the updated > documentation. > --- I do not understand the motivation behind this, which adds yet another location with temporary files in addition to: - LIBGUESTFS_TMPDIR - $TMPDIR by default (which itself is /tmp by default) - LIBGUESTFS_CACHEDIR - /var/tmp by default (with a .guestfs-$UID subdirectory for the appliance) Before this patch, almost all the temporary files are stored directly or in subdirectories of $TMPDIR, except big files such as overlays and OVA extracted content that are in CACHEDIR. With the proposed changes, _all_ the temporary files will be in CACHEDIR, so there are the following problems: - this directory will be cluttered with a lot more files than before - if it is shared, then other places where it is mounted will see the same files - if it is shared, then creating temporary files will possibly mean doing network I/O - if virt-v2v exits uncleantly, there will be a lot more files to cleanup than now - even without being shared, /var/tmp is persistent unlike /tmp (which can be tmpfs-backed on some distros/setups), meaning old temporary files will linger way more

That said, it is not clear to me why /var/tmp should be shared among containers.

> diff --git a/docs/virt-v2v.pod b/docs/virt-v2v.pod > index ed95fdc8e..dbfd10cad 100644 > --- a/docs/virt-v2v.pod > +++ b/docs/virt-v2v.pod > @@ -1206,8 +1206,9 @@ possible. > > =head3 Disk space > > -Virt-v2v places potentially large temporary files in C<$TMPDIR> (which > -is F</var/tmp> if you don't set it). Using tmpfs is a bad idea. Regardless of this patch, this bit is not correct: - libguestfs does not places large files in $TMPDIR (but in CACHEDIR) - $TMPDIR is not /var/tmp by default, but /tmp