Messages in this thread | | | Subject | Re: [RFD] FS behavior (I/O failure) in kernel summit | From | Dave Kleikamp <> | Date | Tue, 14 Jun 2005 08:22:33 -0500 |
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On Mon, 2005-06-13 at 15:53 -0400, fs wrote:
> 1) When I/O failure occurs(e.g.: unrecoverable media failure - USB > unplug), FS should > a. shutdown the FS right now(XFS does this) > b. try to make the media serve as long as possible(EXT3 remounts > read-only, cache is still valid for read) > c. do not care, just print some kernel debugging info(EXT2 JFS > ReiserFS)
In practice, JFS will typically do b. In some cases, an operation may simply return -EIO (or not even that if the write is asynchronous), but eventually, a failure to read or write metadata will lead to the file system being mounted read-only. Like ext2/3, this behavior is configurable with the errors= mount option.
It's possible that JFS may behave like c for a short time, or if an I/O error is isolated.
> 2) When I/O failure occurs, FS should > a. give a unified error > b. give errors according to the FS type > > 3) the returned errno should be > a. real cause of failure, e.g. USB unplug returns EIO > b. cause from FS, e.g. USB unplug made FS remount read-only, > so open(O_RDONLY) returns ENOENT while open(O_RDWR) returns > EROFS > c. errno means nothing, you already get -1, that's enough
I'm not sure I understand the difference between 2) & 3).
If 1)b. applies, then 3)b. makes sense. The initial error causes the file system to be mounted read-only. The original error is history, so any additional errors must make sense in the current context. Trying to write to a read-only filesystem should return -EROFS. Any new I/O errors may return -EIO. I'm not sure about -ENOENT, but it probably makes sense from the context of the code returning the error.
> Unfortunately, recent kernel FSes give mixed answers to the above > questions. As an end user/developer, this is really BAD! Also, there's > no correspondent docs/standard, 'de facto' standard varies for different > people. > > So, we propose 1)a 2)a 3)a as the right behavior. We really hope FS > maintainers can give us a unified answer on this issue, or AT LEAST > positive feedback. If possible, have a discussion in the Kernel Summit.
I don't agree. I think 1)b is the most useful for most purposes. Most users would like to be able to recover as much data as possible if a disk starts failing. Allowing the volume to remain mounted read-only allows this without risking further damage to the file system.
-- David Kleikamp IBM Linux Technology Center
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