CODEWITHSUNDEEP
unix
jwookie
jwookie

Reputation: 71

if interrupt happens how does unix kernel determine which process its for

Lets say Unix is executing process A and an interrupt at higher level occurs. Then OS get a interrupt number and from IVT it looks up the routine to call.

Now how does the OS know that this interrupt was for process A and not for process B. It might have been that process B might have issued a disk read and it came back while OS was executing process A.

Thanks

Upvotes: 0

Views: 453

Answers (2)

ypnos
ypnos

Reputation: 52317

You are talking about a hardware interrupt and these are not targeted at processes.

If a process A requests a file, the filesystem layer, which already resides in the kernel, will fetch the file from the block device. The block device itself is handled by a driver.

When the interrupt occurs, triggered by the block device, the OS has this interrupt associated with the driver. So the driver is told to handle the interrupt. It will then query which blocks were read and see for what it requested them.

After the filesystem is told that the requested data is ready, it may further process it. Then, the process leaves blocked state.

In the next round of the scheduler, the scheduler may select to wake up this process. It may also select to wake up another process first.

As you can see, the interrupt occurance is fully disconnected from the process operation.

Upvotes: 1

S.Lott
S.Lott

Reputation: 391818

Start with this: http://en.wikipedia.org/wiki/MINIX

Go buy the book and read it; it will really help a lot.

Interrupts aren't "for" processes. They're for devices and handled by device drivers.

The device driver handles the interrupt and updates the state of the device.

If the device driver concludes that an I/O operation is complete, it can then update the its queue of I/O requests to determine which operation completed. The operation is removed from the queue of pending operations.

The process which is waiting for that operation is now ready-to-run and can resume execution.

Upvotes: 3

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