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SubjectRe: attempt to access beyond end of device
On Thu, Dec 07, 2000 at 05:34:28PM +0100, Andries Brouwer wrote:
> On Thu, Dec 07, 2000 at 04:56:59PM +0100, Jan Niehusmann wrote:
> > That means that if blk_size[major][MINOR(bh->b_rdev)] == 0, the request
> > is canceled but no message is printed. Shouldn't there be a warning message?
>
> Maybe that code fragment is mine. If so, then at some point
> in time I decided that the answer to your question is no.

As a potential real-world case (but possibly unrelated), I had an
interesting situation crop-up while I was playing with the loopback
filesystems.

If you just use the program-tools, you end up with a situation like:

losetup <blah> [close all] dd <blah> [close all] losetup -d [blah]

In my case, I was making a standalone program that did it all in one
program and I messed up in the ordering of the close() and the LOOP_CLR_FD.

I'm pretty sure that (with my small 10K test dataset) the I/O between
the loopback device and the looped file was never hitting the disk.
If I LOOP_CLR_FD before I closed, I ended up with bad data in the looped
file and kernel errors syslogged:

kernel: attempt to access beyond end of device
kernel: 07:00: rw=1, want=1, limit=0
kernel: dev 07:00 blksize=0 blocknr=0 sector=0 size=1024 count=1

I tended to get 10 of those, one for each of the 10 1K blocks in
my test dataset.

Doing the close() then the LOOP_CLR_FD got rid of the errors.
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