bug#13391: dd silently ignores lseek error

[Pádraig Brady]

On 01/08/2013 08:55 PM, Paul Eggert wrote:
> On 01/08/13 10:11, Neil Klopfenstein wrote:
> > Note that it begins reading at the _beginning of the ar file_ -- the 'skip'
> > argument has failed silently.
>
> But the 'skip' hasn't failed.  It's merely being implemented via 'read'
> rather than via 'lseek'.  The records are being skipped correctly.
>
> It might be useful to give dd a new option, which causes it
> to insist on lseeking rather than reading in cases like these,
> and to report an error if the lseek fails.

I had a look around for a tool to verify
that a file/device supports the seek operation
and couldn't find one.
So this seems like useful functionality.
Worth applying the attached?

thanks,
Pádraig.

dd-flag-seekable.diff
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