Re: dd skip bug?

[Brock Noland]

On Wed, Apr 16, 2008 at 7:01 PM, Pádraig Brady <address@hidden> wrote:
> dd handles skip weirdly
>
>  disk=/dev/sda8
>  dd if=$disk bs=8M count=1 skip=1000 of=/dev/null  #ok
>  dd if=$disk bs=8M count=1 skip=1000K of=/dev/null #reads whole disk! as seek 
> fails
>
>  I had a 10s look at the source and noticed a comment
>  saying POSIX doesn't specify what we should do when
>  skipping past the end of input. For seekable files though,
>  reading the whole thing is unexpected to me at least.
>  I would expect it to do:
>
>  if (seekable && !seek(skip_len))
>     exit(EXIT_FAILURE);

It looks me that the offset is too large? strace shows:
_llseek(0, 8589934592000, 0xbff7efb0, SEEK_CUR) = -1 EINVAL (Invalid argument)

Where as strace dd if=/dev/hda2 of=/dev/null bs=8M skip=10 shows:
_llseek(0, 83886080, [83886080], SEEK_CUR) = 0

I agree that I would expect if the file is seekable and seek fails, dd
would exit. But here it looks like we just cannot seek that large of
an offset?

Respectfully,
Brock