a unifying abstraction for mobile data management

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					quFiles: a unifying abstraction
for mobile data management
                      Kaushik Veeraraghavan*
                               Ed Nightingale†
                                  Jason Flinn*
                                 Brian Noble*

                       * University of Michigan
             †   Microsoft Research (Redmond)
        Mobility is problematic
Battery lifetime Bandwidth & Latency                   Platform diversity




        Trust
                     Each solution
                     implemented in
                     isolation
                Kaushik Veeraraghavan, HotMobile '08                    2
                                                                        2
   Why are they really the same?
Energy-aware adaptation           Odyssey                   Plumber (redaction)




  • Observation: monolithic re-implementations of same idea
  • Idea: select representation of data based on context


                     Kaushik Veeraraghavan, HotMobile '08                         3
  quFiles: a unifying abstraction
• Multiplexes different views of a single logical object
   – Implemented as a new file system object
   – Encapsulates messy details of logical object


• Context-aware mechanism to select the best view
   – Representation selected by a file system extension
   – Context: battery status, connectivity, screen size …




                   Kaushik Veeraraghavan, HotMobile '08     4
                                                            4
Example: Format replication




     Kaushik Veeraraghavan, HotMobile '08   5
                                            5
quFiles provide context-aware views




         quFile resolves to
         application-specific
         representation

           Kaushik Veeraraghavan, HotMobile '08   6
                                                  6
                            Outline
•   Motivation
•   Design & Implementation
•   Applications
•   Open questions
•   Conclusion




                 Kaushik Veeraraghavan, HotMobile '08   7
                                                        7
                            Goals
• Transparency
  – File system encapsulates concrete details
• Backwards compatibility
  – No application modification
• Simplicity
  – No extensive file system changes
• Extensibility
  – Application-specific policy

                Kaushik Veeraraghavan, HotMobile '08   8
                                                       8
         Background: BlueFS
• Blue File System [OSDI ’04]
  – Distributed file system
  – Supports mobile clients including CEDs




                              BlueFS Server

               Kaushik Veeraraghavan, HotMobile '08   9
                    Transparency

                 Photo
                 Transcoder




• Transcoder creates and populates quFile
• Transformations (delete, move etc.)
   – Applied to both the original file and its transcodings
                   Kaushik Veeraraghavan, HotMobile '08       10
                                                              10
                       Simplicity
• quFiles are just special directories
  – Distinguished via FS mode or name
  – Contain names and references to file system objects

• Re-use existing directory code
  – BlueFS kernel: 444 LOC


• File system modifications
  – Readdir & Lookup
     • Policy determines object name, version
     • Modify lookup to check dirent within quFile

                 Kaushik Veeraraghavan, HotMobile '08     11
                                                          11
                      Extensibility
• quFile includes a link to resolution policy
• Policy runs in file system namespace
   – Sprockets [USENIX ’07]
      • New form of software-fault-isolation
      • Safely execute dynamic plugins
• Easy to write
   – 6 application policies
   – average 160 LOC



                   Kaushik Veeraraghavan, HotMobile '08   12
                                                          12
Application: Resource management
• Trade storage space for power




mp3
              WAV                                    WAV

• Cache larger, power-efficient WAV with mp3
  – 11% battery lifetime gain on an iPAQ

              Kaushik Veeraraghavan, HotMobile '08         13
                                                           13
   Resource-Aware Directories




                 NULL



• Dynamic directory listing
  – Only list files that are viewable given current constraints
                Kaushik Veeraraghavan, HotMobile '08              14
                                                                  14
                            Odyssey


NULL




• Different clients; connected at different bitrates
    – Each view different version of video
    – Gimme my PhD!
                    Kaushik Veeraraghavan, HotMobile '08   15
                                                           15
              Open Questions
• What other applications can quFiles support?


• Can we compose data management policies?
  – How should conflicts be resolved?
  – Should policies be assigned priorities?




               Kaushik Veeraraghavan, HotMobile '08   16
                                                      16
          More open questions
• What if users want to edit lower-fidelity files?
  – Default: deny edits
  – Exceptions
     • Lossless
     • Metadata (e.g.: id3)
  – Permitted if application provides policy




                Kaushik Veeraraghavan, HotMobile '08   17
                                                       17
                    Conclusion
• quFiles
  – A unifying abstraction
  – Multiplexes different views onto single logical object
  – Context-aware mechanism to select the best view


• Easy to incorporate in file system
• Easy to add new policies

• Questions?
               Kaushik Veeraraghavan, HotMobile '08          18
                                                             18

				
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posted:3/31/2011
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