Re: detaching existing extensions with new systemd extension attach

serenissi <serenissi@xxxxxxxxxxxxx> · Thu, 28 Nov 2024 05:55:27 +0530



    What is the usecase for this? sysexts are extensions to /usr (and
      /opt). Services don't write to /usr usually (extensions are
      usually read only too). Anything being read is opened as a fd
      which survives the unmount-mount operation. I can't think of any
      reason a service would want to "lock" /usr mountpoint.
    Further if your service need to use binaries from patch extension
      then you want to reload it somehow anyway.

    
    Can you explain a bit more?
    serene

    
    On 10/28/24 21:30, Umut Tezduyar
      Lindskog wrote:

    
        Hello systemd,
         
        We are looking into systemd system
          extensions for quick patching our immutable images while we
          are updating and rolling out the patched immutable image. 
         
        One thing that is stated in the
          documentation is that before attaching a new extension, all
          previous extensions are deattached and everything are attached
          again. We understand that this sequence is needed for
          overlayfs stacking in case something has changed in the stack
          with the new extension. 
         
        For our use case, we would like to be able
          to push multiple patch extensions (ex: couple of days apart)
          while keeping the service downtime to a minimum.
          Technically we believe that if the extensions are not
          overlapping there is no need to detach already attached
          extensions. There is no built in option in systemd extensions
          to keep the existing extensions right? Due to how overlayfs
          works, they temporarly need to be removed and thenbrought up again, during a refresh
          operation. 
         
        While on the topic, we have investigated
          other file systems. One we put our attention to is mergerfs,
          which is a fuse file system to allows "mount points" to be
          dynamically added/removed without doing a mount/unmount. Is
          there support in systemd extensions to let system extension
          work with other file systems than overlayfs?
         
        Thanks
        Umut
         
      
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