linux-kernel - Re: [PATCH v2 2/3] fpga manager: framework core

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Date:	Fri, 24 Oct 2014 22:00:13 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Pavel Machek <pavel@...x.de>
Cc:	atull@...nsource.altera.com, gregkh@...uxfoundation.org,
	jgunthorpe@...idianresearch.com, hpa@...or.com, monstr@...str.eu,
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	yvanderv@...nsource.altera.com
Subject: Re: [PATCH v2 2/3] fpga manager: framework core


> > +int fpga_mgr_write(struct fpga_manager *mgr, const char *buf, size_t count)
> > +{
> > +	int ret;
> > +
> > +	if (test_and_set_bit_lock(FPGA_MGR_BUSY, &mgr->flags))
> > +		return -EBUSY;
> > +
> > +	dev_info(mgr->dev, "writing buffer to %s\n", mgr->name);
> > +
> > +	ret = __fpga_mgr_write(mgr, buf, count);
> > +	clear_bit_unlock(FPGA_MGR_BUSY, &mgr->flags);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(fpga_mgr_write);
> 
> Is the EBUSY -- userspace please try again, but you don't know when to
> try again -- right interface? I mean, normally kernel would wait, so
> that userland does not have to poll?

And if userland has to also support polling you must support poll/select
on the file handle so it knows when to retry the I/O.

The error should be EAGAIN for a retriable write with O_NDELAY set.

Alan
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