linux-kernel - Re: [PATCH 0/7] IB/hfi1: Remove write() and use ioctl() for user access

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Message-ID: <20160416191917.GY25498@ZenIV.linux.org.uk>
Date:	Sat, 16 Apr 2016 20:19:17 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Leon Romanovsky <leon@...n.nu>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ira Weiny <ira.weiny@...el.com>,
	Dennis Dalessandro <dennis.dalessandro@...el.com>,
	dledford@...hat.com, linux-rdma@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] IB/hfi1: Remove write() and use ioctl() for user
 access

On Sat, Apr 16, 2016 at 09:00:42AM +0300, Leon Romanovsky wrote:
> On Fri, Apr 15, 2016 at 05:37:32PM -0600, Jason Gunthorpe wrote:
> > On Sat, Apr 16, 2016 at 12:23:28AM +0300, Leon Romanovsky wrote:
> > 
> > > Intel as usual decided to do it in their way and the result is presented
> > > on this mailing list.
> > 
> > Dennis was pretty clear he was going to send the patches to address
> > Al's concern, which he has done.
> > 
> > I was also pretty clear I was looking to get rid of the char dev :)
> 
> Yes, and I was pretty clear that we need to converge on one common API
> prior to converting old code (including drivers in staging) in order to
> do it once only.

While we are at it, could the person who'd come up with ui_lseek() be located
and made to stand up and explain the rationale behind the SEEK_END semantics
therein?  To quote the manpage (and paraphrase just about any introductory
textbook):
       SEEK_END
              The file offset is set to the size of the file plus offset bytes.

I'm really curious - which part of "plus" might have lead to
        case SEEK_END:
                offset = ((dd->kregend - dd->kregbase) + DC8051_DATA_MEM_SIZE) -
                        offset;
and, if its author has decided that of course it _must_ have meant "minus",
why had he or she failed to post a correction to the manpage?  Or, on the
off-chance that this "plus" might have something to do with reality,
experimented with some file, for that matter.

Folks, this is a well-earned "F".  And not just for Unix Programming 101 -
the same semantics applies to fseek(3), which is a part of C standard.
Incidentally, lseek(fd, 0, SEEK_END) is "seek to end", not "fail with EINVAL".

As for the use of ioctl...  Frankly, considering the above, it does sound like
"that'll make them STFU about the weirdness - ioctl *is* weird, so there!"

Single-consumer APIs stink, film at 11...