linux-ext4 - Re: Bug: Large writes can fail on ext4 if the write buffer is not empty

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Message-ID: <20120420021211.GD9541@dastard>
Date:	Fri, 20 Apr 2012 12:12:11 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Jouko Orava <jouko.orava@...sinki.fi>, linux-ext4@...r.kernel.org,
	Zheng Liu <gnehzuil.liu@...il.com>
Subject: Re: Bug: Large writes can fail on ext4 if the write buffer is not
 empty

On Thu, Apr 19, 2012 at 09:15:40AM -0500, Eric Sandeen wrote:
> On 4/19/12 8:10 AM, Jouko Orava wrote:
> > I'd also like to point at the real bug here, in Jouni's original strace:
> > 
> > 	writev(3, [{"\0\0\0\0\0\0\0\0", 8}, {"", 2147483648}], 2) = -2147483640
> > 
> > The syscall returns a negative value, which is not the actual number of
> > bytes written (since it is 32-bit wrapped), and errno has not been
> > changed. There is no way for userspace to handle this result correctly!
> > 
> > There is no way anyone sane should just gloss over this saying
> > "programmer fault, you're doing it wrong".
> > This is a real bug, and deserves fixing sooner rather than later.
> 
> Agreed, I think Dave was a little to quick on the draw on his reply.  :)

I was pointing the -EFAULT error in the second syscall which was
just being passed the 2GB sized buffer, not the above error from the
first syscall.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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