Re: [pve-devel] [PATCH qemu v2 07/21] PVE backup: add fleecing option

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Wed, Apr 10, 2024 at 11:30:59AM +0200, Fiona Ebner wrote:
> Am 08.04.24 um 14:45 schrieb Wolfgang Bumiller:
> > On Fri, Mar 15, 2024 at 11:24:48AM +0100, Fiona Ebner wrote:
> >> @@ -581,6 +682,14 @@ static void create_backup_jobs_bh(void *opaque) {
> >>      aio_co_enter(data->ctx, data->co);
> >>  }
> >>  
> >> +/*
> >> + * EFI disk and TPM state are small and it's just not worth setting up fleecing for them.
> >> + */
> >> +static bool device_uses_fleecing(const char *device_id)
> > 
> > Do we really want this?
> > 
> > IMO we already have enough code trying to distinguish "real" disks from
> > efidisks and tpmstate files.
> > 
> > AFAICT we do check whether the hmp command to *create* the fleecing
> > drives actually works, so... (see below)
> > 
> >> +{
> >> +    return strncmp(device_id, "drive-efidisk", 13) && strncmp(device_id, "drive-tpmstate", 14);
> >> +}
> >> +
> >>  /*
> >>   * Returns a list of device infos, which needs to be freed by the caller. In
> >>   * case of an error, errp will be set, but the returned value might still be a
> >> @@ -588,6 +697,7 @@ static void create_backup_jobs_bh(void *opaque) {
> >>   */
> >>  static GList coroutine_fn *get_device_info(
> >>      const char *devlist,
> >> +    bool fleecing,
> >>      Error **errp)
> >>  {
> >>      gchar **devs = NULL;
> >> @@ -611,6 +721,31 @@ static GList coroutine_fn *get_device_info(
> >>              }
> >>              PVEBackupDevInfo *di = g_new0(PVEBackupDevInfo, 1);
> >>              di->bs = bs;
> >> +
> >> +            if (fleecing && device_uses_fleecing(*d)) {
> >> +                g_autofree gchar *fleecing_devid = g_strconcat(*d, "-fleecing", NULL);
> >> +                BlockBackend *fleecing_blk = blk_by_name(fleecing_devid);
> >> +                if (!fleecing_blk) {
> > 
> > ...so instead of this, we could just treat the absence of a fleecing
> > BlockBackend *not* as an error, but as deliberate?
> > 
> 
> Yes, we could. But the check gives protection against potential (future)
> bugs where we can't find the fleecing device for some other reason.
> Without the check, we'd just quietly continue and it would be hard to
> notice that something is wrong. So I'm slightly in favor of keeping it.
> If you still want me to remove it, I'll do it in v3.

Mh, makes sense. Let's keep it then.