quFiles: 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)

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Mobility is problematic
Bandwidth Latency
Platform diversity
Battery lifetime
Trust
Each solution implemented in isolation
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Why are they really the same?

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

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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

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Example Format replication
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quFiles provide context-aware views
quFile resolves to application-specific
representation
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Outline

• Motivation
• Design Implementation
• Applications
• Open questions
• Conclusion

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Goals

• Transparency
• File system encapsulates concrete details
• Backwards compatibility
• No application modification
• Simplicity
• No extensive file system changes
• Extensibility
• Application-specific policy

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Background BlueFS

• Blue File System OSDI 04
• Distributed file system
• Supports mobile clients including CEDs

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Transparency
Photo Transcoder

• Transcoder creates and populates quFile
• Transformations (delete, move etc.)
• Applied to both the original file and its
  transcodings

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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

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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

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Application Resource management

• Trade storage space for power
• Cache larger, power-efficient WAV with mp3
• 11 battery lifetime gain on an iPAQ

mp3
WAV
WAV
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Resource-Aware Directories
NULL

• Dynamic directory listing
• Only list files that are viewable given current
  constraints

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Odyssey
NULL

• Different clients connected at different
  bitrates
• Each view different version of video
• Gimme my PhD!

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Open Questions

• What other applications can quFiles support?
• Can we compose data management policies?
• How should conflicts be resolved?
• Should policies be assigned priorities?

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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

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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?

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