[RFC qemu-server 0/5] drive: account for differing TPM sizes

[Thomas Ellmenreich <t.ellmenreich@proxmox.com>]

Our current systems to handle TPM drives always assume that the disks have a
fixed 4MiB size that cannot be changed even if that may not be the case. In
situations where the granularity of the backing storage exceeds the 4MiB, an
allocation of a TPM drive will be at least as big as the granularity of said
backing storage.

To solve this mismatch in a very simple way, the default size is retained for
allocation. Only after the allocation do we check the actual size of the
created TPM disk and update the configuration accordingly. A minimum size of
4MiB is always applied to situations where that may not be the case.

In the case of migrations, movement and cloning of disks, we just refer to the
actual disk size instead of the TPM size constant. Doing so also makes it now
possible to move a larger (than 4MiB) TPM disk to a different storage.

Open Questions
--------------

1. During a migration a TPM disk might change from a storage with 4MiB
   granularity to a storage with 64MiB granularity. As already mentioned, the
   TPM disk's size is then automatically increased. The fix I have implemented
   for this, performs a "brute" `qm disk rescan --vmid` on the remote. This
   does the job, but also much more.

   To avoid all of the other side effects of a rescan, I could extend `qm disk
   rescan` to also take another parameter that specifies the disk and so Avoid
   any of the other side effects of calling a rescan on the whole VM. could
   This approach be better? or is there a even better approach?

2. The rescan is currently disabled for remote migrations, but it should also
   be safe for those. So does it make sense to also implement the rescan for
   remote migrations?

3. A small thing, but how should I handle errors produced by PVE::Tools::run_command?
   I didn't quite understand if run_command returns an error if an error is
   emitted by the internal command. If that is not the case, the context is
   never actually shown.


qemu-server:

Thomas Ellmenreich (5):
  drive: improve and extend TPM drive size helpers
  drive: update TPM size on creation
  drive: read actual size when cloning TPM drive
  tests: make qm mock accept disk command
  drive: rescan drives after migrating to different storage

 src/PVE/API2/Qemu.pm                      | 16 ++++++++++----
 src/PVE/QemuMigrate.pm                    | 19 +++++++++++++---
 src/PVE/QemuServer.pm                     | 27 ++++++++++++++++++++---
 src/test/MigrationTest/QemuMigrateMock.pm |  2 ++
 4 files changed, 54 insertions(+), 10 deletions(-)


Summary over all repositories:
  4 files changed, 54 insertions(+), 10 deletions(-)

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