Re: [RFD] What error should FS return when I/O failure occurs?

[fs <fs@ercist.iscas.ac.cn>]

On Tue, 2005-05-17 at 14:26, Bryan Henderson wrote:
> >Yes, we're sure to abort the operation, but we can't use 
> >exit(EXIT_FAILURE) directly. For HA environment, we should
> >identify the cause of the error, take correspondent action,
> >right? So we need to get the right error.
> 
> You mean a computer program will take the correspondent action?  I think 
> it would take a remarkably intelligent program to respond appropriately to 
> particular failures -- especially if the program isn't tailored to a very 
> specific environment.  In practice, all I ever see a binary response -- 
> one for success, one for failure.  The errno is used at most for giving a 
> three word explanation to a human so the human can respond.  That's why 
> people don't take this issue seriously.
> 
> "pass the errno up" is definitely a layering violation and cheap 
> architecture.  It's why the 3 word description you get is often 
> meaningless -- it's telling you about a failure deep in computations you 
> aren't even supposed to know about.  I myself stay away from errnos where 
> possible and produce error information in English text, with each layer 
> adding information meaningful at that layer.  But where we're sticking 
> with classic errnos, it just doesn't make sense to work really hard on it.
> 
> Nonetheless, I think there's broad agreement, and the current discussion 
> is consistent with it, that if write() fails due to an I/O error, the 
> errno should be EIO.  Whether it's formally specified or not, the standard 
> is there.  That ext3 returns EROFS is either a bug or an implementation 
what standard do you mean?
> convenience compromise or a case where the actual failure is more 
> complicated than you imagine (maybe an operation fails and gets retried -- 
> the original failure caused an automatic switch to R/O and the retry 
> failed because of the R/O status.  Errnos are definitely not sufficient to 
> give you the whole chain of causation for a failure -- if it gives you 
> even the immediate cause, you should feel fortunate).
I suggest you visit our project, see the testing result,
http://developer.osdl.jp/projects/doubt/fs-consistency-and-coherency
For each test case, different FS returns different result.
>From user's perspective, it's really annoying, so, there should be a 
standard which constraints the error type. Otherwise, different fs
can return whatever they want, regardless of the user's need. 
> --
> Bryan Henderson                          IBM Almaden Research Center
> San Jose CA                              Filesystems
>