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From: Christoph Hellwig <hch@lst.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>, Miklos Szeredi <mszeredi@suse.cz>,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 3/5] fs: remove ki_nbytes
Date: Mon, 2 Feb 2015 15:26:17 +0100	[thread overview]
Message-ID: <20150202142617.GC17447@lst.de> (raw)
In-Reply-To: <20150202081431.GX29656@ZenIV.linux.org.uk>

On Mon, Feb 02, 2015 at 08:14:31AM +0000, Al Viro wrote:
> 13) two odd drivers/usb/gadget instances.  I have conversion for f_fs.c,
> but legacy/inode.c (ep_read() et.al.) is trickier.  The problem in there
> is that writev() on a single-element vector is *not* equivalent to plain
> write().  The former treats the wrong-direction endpoint as EINVAL; the
> latter does
>                 if (usb_endpoint_xfer_isoc(&data->desc)) {
>                         mutex_unlock(&data->lock);
>                         return -EINVAL;
>                 }
>                 DBG (data->dev, "%s halt\n", data->name);
>                 spin_lock_irq (&data->dev->lock);
>                 if (likely (data->ep != NULL))
>                         usb_ep_set_halt (data->ep);
>                 spin_unlock_irq (&data->dev->lock);
>                 mutex_unlock(&data->lock);
>                 return -EBADMSG;
> instead.  IOW, for isochronous endpoints behaviour is the same, but the
> rest behaves differently.  If not for that, that sucker would convert
> to (3) easily;

I would bet the behavior difference is a bug, might be worth to Cc the
usb folks on this issue.  I bet we'd want the more complex behavior
for both variants.

> 14) ipathfs and qibfs: seriously different semantics for write and writev/AIO
> write.  As in "different set of commands recognized"; AIO write plays like
> writev, whether it's vectored or not (and it's always synchronous).
> I've no idea who had come up with that... highly innovative API or why
> hadn't they simply added two files (it's all on their virtual filesystem,
> so they had full control of layout) rather that multiplexing two different
> command sets in such a fashion.
> 
> 15) /dev/snd/pcmC*D*[cp].  Again, different semantics for write and writev,
> with the latter wanting nr_seqs equal to the number of channels.  AIO
> non-vectored write fails unless there's only one channel.  Not sure how
> ALSA userland uses that thing; AIO side is always synchronous, so it might
> be simply never used.  FWIW, I'm not sure that write() on a single-channel
> one is equivalent to 1-element writev() - silencing-related logics seem to
> differ.

For these weirdos we can pass down a flag in the kiocb about the source
of the I/O.  We'll need that flags field for non-blocking buffered reads
and per-I/O O_SYNC anyway, and it will be very useful for fixing the
races around changing the O_DIRECT flag at run time.

  reply	other threads:[~2015-02-02 14:26 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-27 17:55 [RFC] split struct kiocb Christoph Hellwig
2015-01-27 17:55 ` [PATCH 1/5] fs: don't allow to complete sync iocbs through aio_complete Christoph Hellwig
2015-01-28 15:30   ` Miklos Szeredi
2015-01-28 16:57     ` Christoph Hellwig
2015-01-31  3:01       ` Maxim Patlasov
2015-01-27 17:55 ` [PATCH 2/5] fs: saner aio_complete prototype Christoph Hellwig
2015-01-31 10:04   ` Al Viro
2015-01-27 17:55 ` [PATCH 3/5] fs: remove ki_nbytes Christoph Hellwig
2015-01-31  6:08   ` Al Viro
2015-02-02  8:07     ` Christoph Hellwig
2015-02-02  8:11       ` Al Viro
2015-02-02  8:14         ` Al Viro
2015-02-02 14:26           ` Christoph Hellwig [this message]
2015-02-04  8:34             ` Al Viro
2015-02-04 18:17               ` Alan Stern
2015-02-04 19:06                 ` Al Viro
2015-02-04 20:30                   ` Alan Stern
2015-02-04 23:07                     ` Al Viro
2015-02-05  8:24                       ` Robert Baldyga
2015-02-05  8:47                         ` Al Viro
2015-02-05  9:03                           ` Al Viro
2015-02-05  9:15                             ` Robert Baldyga
     [not found]                       ` <20150204230733.GK29656-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2015-02-05 15:29                         ` Alan Stern
2015-02-06  7:03                           ` Al Viro
     [not found]                             ` <20150206070350.GX29656-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2015-02-06  8:44                               ` Robert Baldyga
2015-02-07  5:44                           ` Al Viro
2015-02-07  5:48                             ` [PATCH 1/6] new helper: dup_iter() Al Viro
2015-02-07  5:48                             ` [PATCH 2/6] gadget/function/f_fs.c: close leaks Al Viro
2015-02-07  5:48                             ` [PATCH 3/6] gadget/function/f_fs.c: use put iov_iter into io_data Al Viro
2015-02-07  5:48                             ` [PATCH 4/6] gadget/function/f_fs.c: switch to ->{read,write}_iter() Al Viro
2015-02-07  5:48                             ` [PATCH 5/6] gadgetfs: use-after-free in ->aio_read() Al Viro
2015-02-07  5:48                             ` [PATCH 6/6] gadget: switch ep_io_operations to ->read_iter/->write_iter Al Viro
2015-02-02 14:20         ` [PATCH 3/5] fs: remove ki_nbytes Christoph Hellwig
2015-01-27 17:55 ` [PATCH 4/5] fs: split generic and aio kiocb Christoph Hellwig
2015-01-27 17:55 ` [PATCH 5/5] fs: add async read/write interfaces Christoph Hellwig
2015-01-31  6:29   ` Al Viro

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