Messages in this thread | | | From | Neil Brown <> | Date | Mon, 6 Sep 2004 11:36:50 +1000 | Subject | Re: bug in md write barrier support? |
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On Saturday September 4, axboe@suse.de wrote: > On Sat, Sep 04 2004, Neil Brown wrote: > > On Friday September 3, hch@lst.de wrote: > > > md_flush_mddev just passes on the sector relative to the raid device, > > > shouldn't it be translated somewhere? > > > > Yes. md_flush_mddev should simply be removed. > > The functionality should be, and largely is, in the individual > > personalities. > > Yes, sorry I was a little lazy there even though I followed the plugging > conversion :( > > > Is there documentation somewhere on exactly what an issue_flush_fn > > should do (is it allowed to sleep? what must happen before it is > > allowed to return, what is the "error_sector" for, that sort of thing). > > It is allowed to sleep, you should return when the flush is complete. > error_sector is the failed location, which really should be a dev,sector > tupple.
Could I get a little more information about this function please. I've read through the code, and there isn't much in the way of examples to follow: only reiserfs uses it, only scsi-disk and ide-disk supports it (I think).
It would seem that this is for write requests where b_end_io has already been called, indicating that the data is safe, but that maybe the data isn't really safe after-all, and blk_issue_flush needs to be called.
I would have thought that after b_end_io is called, that data should be safe anyway. Not so?
How do you tell a device: it is OK to just leave the data is cache, I'll call blk_issue_flush when I want it safe. Is this related to barriers are all??
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