Re: [PATCH V2 0/2] Auto stop async-write on block device when device removed.

From: Jeff Moyer
Date: Wed Sep 25 2013 - 11:45:17 EST

majianpeng <majianpeng@xxxxxxxxx> writes:

>>The bigger question is whether we want to change this long-standing
>>behaviour of how our write-back cache works. I don't know that it's
>>really worth it, honestly. If you want to ensure data is on disk, you
>>open the file O_SYNC or you issue an fsync, and those calls will return
>>an error for a removed block device. So, I guess I'll ask the same
>>question again: why are you looking at this? Is there some application
>>you care about that does buffered I/O to the block device and never does
>>an fsync?
> Yes, for my company, we used our filesystem in userspace on block-device.
> For the performance, we used buffer-wrtite not sync-write.
> For my workload, we allow user to remove disk whether disk working or not.
> Now, we check the state of disk from /proc/partitions at the same interval.
> This patchset don't change write-back cache works.It only let vfs know
> the state of lower-device. I think it make a sense.

I'm still curious to know how you maintain a consistent file system
without the use of fsync, but that's an unrelated issue.

I looked at the rescan partition code path more closely, and it will
only really trigger if the partitions themselves aren't open. So, I
don't think there is a problem in your approach.

I'll ack patch 1. I still think patch 2 is not neessary. Please
correct me if I'm wrong.

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