Lecture 20

• Lecture 20
  • Video
  • Virtualizing I/O
  • I/O Devices
  • Virtualizing Dedicated devices
  • Partitioned Devices
  • Shared Devices
  • Spooled Device
  • Virtualizing I/O activity
    • I/O Operation level
    • Device Driver Level
    • System Call level

Video

link

Virtualizing I/O

• VMM has to interact with so many devices
• guest Oss expect to interact with the devices
• startegy is vitualize device do guest os ko, also jab activity ho, virtualize that activity

I/O Devices

• dedicated devices
  • cannot be shared
  • keyboard, mouse
  • switched from one guest os to other
• partitioned devices
  • hard disk can be partitioned and presented as virtual hard disk
• shared
  • network interface card
    • cannot be dedicated, asynchronously data aata na bhai
• spooled devices
  • printer
    • hai shared but cannot be fine grained
    • unless one file is completely printed, it cannot be removed
  • sharing is coarse grained way
  • number of pages ke terms hai na ki kitne ms me
• non-existent physical devices
  • device not exist, but attach to vm
  • eg, switch b/w guest OSs, VMM will have a virtual device which does this

Virtualizing Dedicated devices

• not needed to virtualize
• simple attach device to guest os
• bas req are routed still through vmm

Partitioned Devices

• partitioned hard disk is actually a file in actual(physical)
• mapping has to be remembered by vmm
• write req aayi, vmm has to translated to sector and tracj in physical device, and status info bhi bhejni hogi to guest vm back

Shared Devices

• NIC
• has associated virtual nic to each guest vm
• virtual mac/ip address associated hai
• vmm translate requests
• say tcp req aayi, virtual device druiver hota har guest vm me which identify kaha bheju

Spooled Device

• printer spooling is achieved by
  • buffering data to be printed
  • guest os karega
  • vmm has to do spooling across multiple vms
  • we have 2 tables for these
    • one in every guest os
      • for each process
    • one in vmm
      • for each guest vm

Virtualizing I/O activity

• device virtualize karlia
• ab activity
• device attach kia, ab activity kabhi bhi ho sakti
• vmm can try to intercept at system call level or at driver call level(priveledged hi hai na)

I/O Operation level

• vmm traps i/o operns
• diff to know what i/o ho ra, bcz too fine level pe chal rahe honge instructions
• semantic understanding nahi na bhai

Device Driver Level

• device driver jab isa me convert karra
• vmm intercept call to virtual driver and convert to physical driver
• dekh virtual device driver are provided by vmm only
• priveldged hai woh, so vmm ko pata chal jata

System Call level

• best handled by guest os
• bcz usko maybe smjh na aayega
• guest os implement karta hai na