[pve-devel] [PATCH v2 qemu-server 1/2] resize_vm: request new size from storage after resizing

[Dominik Csapak]

[...]
> 
> Please do not apply the second and third patch in this series yet. I 
> thought about this some more and think it makes more sense to always 
> align to a multiple of 1 KiB.

like we discussed off-list, this seems the most-sensible to me,
for your reasons listed below

getting the 'effective' size after allocating would be nice,
but this seems to be only cosmetic which gets fixed by the
next 'rescan' anyway (e.g. on migration) so not so important
right now

> Reasons for this are:
> 
> 1. For volume export/import, in 'write_common_header' we write the size 
> of the file in bytes, in 'read_common_header' there is a check whether 
> the size is a multiple of 1KiB.
> 
> So not all volumes exported with 'pvesm' can be imported with 'pvesm':
> 
> root at rob0 ~ # qm resize 128 scsi2 +512
> Image resized.
> root at rob0 ~ # pvesm export myfs:128/vm-128-disk-0.qcow2 qcow2+size 
> myoddexport --with-snapshots
> 52816+0 records in
> 52816+0 records out
> 216334336 bytes (216 MB, 206 MiB) copied, 0.291073 s, 743 MB/s
> root at rob0 ~ # pvesm import myfs:128/vm-128-disk-1.qcow2 qcow2+size 
> myoddexport --with-snapshots
> import: got a bad size (not a multiple of 1K), aborting.
> 
> 2. Allocating volumes happens with a size in KiB, so maybe resizing 
> should too? Internally we could switch the interface for 
> 'PVE::Storage::volume_resize' to use KiB instead of bytes and we could 
> warn users which pass a non-KiB-multiple to 'qm resize', that we rounded 
> up and didn't use the requested size exactly.
> 
> 3. Many plugins already round the size anyways.
> 
> 
> The same change as here in the first patch is also needed for callers of 
> 'vdisk_alloc', since the size the disk has after allocating might not be 
> the requested size. For example in ZFSPoolPlugin size is aligned to 1M, 
> LVM uses logical extents so the effective size is also often different 
> from the parameter.
> 
> Related: I ran into a weird bug [0] yesterday, where a workaround would 
> require the size being a multiple of 4KiB. But that could be done for 
> the 'vdisk_alloc' call in 'vm_start'.
> 
> [0]: https://bugzilla.proxmox.com/show_bug.cgi?id=2562

have not looked into this too much, but if i have the time will
take a look at this