Re: [pbs-devel] [PATCH proxmox-backup v9 06/26] datastore: add helper for checking if a removable datastore is available

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

On Thu, Apr 25, 2024 at 08:05:27AM +0200, Hannes Laimer wrote:
> On Wed Apr 24, 2024 at 3:30 PM CEST, Wolfgang Bumiller wrote:
> > On Tue, Apr 23, 2024 at 10:29:40AM +0200, Hannes Laimer wrote:
> > > Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
> > > ---
> > >  pbs-api-types/src/maintenance.rs |  2 +-
> > >  pbs-datastore/src/datastore.rs   | 44 ++++++++++++++++++++++++++++++++
> > >  pbs-datastore/src/lib.rs         |  2 +-
> > >  3 files changed, 46 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/pbs-api-types/src/maintenance.rs b/pbs-api-types/src/maintenance.rs
> > > index fd4d3416..4f653ec7 100644
> > > --- a/pbs-api-types/src/maintenance.rs
> > > +++ b/pbs-api-types/src/maintenance.rs
> > > @@ -81,7 +81,7 @@ impl MaintenanceMode {
> > >      /// Used for deciding whether the datastore is cleared from the internal cache after the last
> > >      /// task finishes, so all open files are closed.
> > >      pub fn is_offline(&self) -> bool {
> > > -        self.ty == MaintenanceType::Offline
> > > +        self.ty == MaintenanceType::Offline || self.ty == MaintenanceType::Unmount
> > >      }
> > >  
> > >      pub fn check(&self, operation: Option<Operation>) -> Result<(), Error> {
> > > diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
> > > index f9b986c1..978ebb70 100644
> > > --- a/pbs-datastore/src/datastore.rs
> > > +++ b/pbs-datastore/src/datastore.rs
> > > @@ -14,6 +14,7 @@ use proxmox_schema::ApiType;
> > >  use proxmox_sys::error::SysError;
> > >  use proxmox_sys::fs::{file_read_optional_string, replace_file, CreateOptions};
> > >  use proxmox_sys::fs::{lock_dir_noblock, DirLockGuard};
> > > +use proxmox_sys::linux::procfs::MountInfo;
> > >  use proxmox_sys::process_locker::ProcessLockSharedGuard;
> > >  use proxmox_sys::WorkerTaskContext;
> > >  use proxmox_sys::{task_log, task_warn};
> > > @@ -49,6 +50,39 @@ pub fn check_backup_owner(owner: &Authid, auth_id: &Authid) -> Result<(), Error>
> > >      Ok(())
> > >  }
> > >  
> > > +/// check if a removable datastore is currently available/mounted by using the UUID
> > > +/// to find the `/dev/sdX` path and checking in /proc/self/mountinfo for entries containing it.
> > > +/// If it should mounted, but not in the expected path, so config.path, it is considered not
> > > +/// available.
> > > +pub fn is_datastore_available(config: &DataStoreConfig) -> bool {
> > > +    config.backing_device.as_ref().map_or(true, |uuid| {
> > > +        if let Ok(store_dev_path) = std::fs::read_link(Path::new("/dev/disk/by-uuid").join(uuid))
> > > +            .map(|p| p.to_string_lossy().into_owned())
> > > +            .map(|p| p.replace("../..", "/dev"))
> >
> > ^ Merge the two .maps together and you can drop the into_owned()
> >
> > Also, this is very fragile!
> > `/proc/self/mountinfo` does NOT necessarily contain the final device
> > node.
> > For instance, for LVs you do NOT see `/dev/dm-xy`, but
> > `/dev/mapper/foo-bar`.
> >
> > I pushed an alternative to my `staff` repo's
> > `removable-datastore-review` branch which worked for my testing.
> >
> > There I instead `stat` the backing device and the source device found in
> > the MountInfo and compare their `st_rdev` values.
> >
> This is a very good idea, and does sound more robust. But I don't think
> we actually want to mount LVMs as removable datastores.

Well it's the very first thing I tried and is just an example.

We don't *only* support creating storages by formatting *new* disks.
Users can very much just add a directory of any device, and LVs are just
an example (and since you can activate/deactivate them, they're an easy
test case ;-) )


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