From: Jens Axboe <jens.axboe@xxxxxxxxxx>
Subject: Re: bidi bsg is non-blocking
Date: Tue, 8 May 2007 14:21:34 +0200
> On Tue, May 08 2007, FUJITA Tomonori wrote:
> > > From: Daniel.E.Messinger@xxxxxxxxxxx
> > > Subject: bidi bsg is non-blocking
> > > Date: Mon, 7 May 2007 10:21:18 -0500
> > >
> > > > I'm attempting to use the bidi variant of bsg to talk to an OSD target
> > > > device. I've run into an undesirable situation.
> > > >
> > > > My application has a free-running receive loop (doing a read() on the bsg
> > > > device) waiting for responses to commands sent to bsg by another thread.
> > > > The problem is that the receive thread is getting ENODATA from the read()
> > > > when there are no commands pending. I have NOT set non-blocking.
> > > >
> > > > Note that the old sg driver was quite willing to block until there was a
> > > > response available. I find this scenario greatly preferable.
> > > >
> > > > Could bsg be fixed so that read() blocks when there is nothing to return?
> > >
> > > I think that this is a bug.
> > >
> > > This patch is against the bsg branch in the Jens' git tree.
> > >
> > > I guess that it would be nice to do more cleanups on these parts.
> > >
> > >
> > > From 52a9fcf0af72f212ddd93918b7f9f0f0e706c215 Mon Sep 17 00:00:00 2001
> > > From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
> > > Date: Tue, 8 May 2007 15:57:43 +0900
> > > Subject: [PATCH] fix read ENODATA bug
> > >
> > > This patch fixes a bug that read() gives ENODATA even with a blocking
> > > file descriptor when there are no commands pending.
> > >
> > > This also includes some cleanups.
> > >
> > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
> >
> > Oops, I sent a wrong patch. This is a right one.
>
> Patch looks good, I agree this is the way that bsg should act for a
> blocking read on an "empty" queue.
>
> > + ret = wait_event_interruptible(bd->wq_done, bd->done_cmds);
> > + if (ret) {
> > + bc = ERR_PTR(-ERESTARTSYS);
> > + break;
> > + } else
> > + continue;
> > } while (1);
>
> The else clause is pointless.
Oops.
> Apart from that, it looks sounds. Can you resend?
Sure, I'll resend an updated version shortly.
BTW, any comments on the bidi patch for the block layer?
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