From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anand Jain <Anand.Jain@oracle.com>
Subject: Re: [RFC] Passing stream to userspace
Date: Tue, 16 Aug 2011 10:49:31 +0800
Message-ID: <4E49DABB.5000404@oracle.com>
References: <4E454718.6000206@jan-o-sch.net>
Mime-Version: 1.0
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Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	Chris Mason <chris.mason@oracle.com>,
	Matthew Wilcox <matthew@wil.cx>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org
To: Jan Schmidt <list.btrfs@jan-o-sch.net>
Return-path: <linux-btrfs-owner@vger.kernel.org>
In-Reply-To: <4E454718.6000206@jan-o-sch.net>
List-ID: <linux-btrfs.vger.kernel.org>


Jan,

  I personally like the way we interact with the kernel using the
  /sys or /proc that's a cool way, mainly because no C code is required.
  A generic interface like that (or btrfs-control with more commands
  supported) will enhance troubleshooting and debugging, application
  interface.
  or did I miss anything ?

Cheers, Anand


On 08/12/2011 11:30 PM, Jan Schmidt wrote:
> Hi there,
>
> I was promised you (viro, hch) have a decided opinion on this topic. The
> original mail ("Getting a lot of fs-generated information to user
> space") contains a lot of background and is way too long. Point is: I
> want to get a bunch of data generated by the kernel (btrfs) to userland
> (really).
>
> Matthew Wilcox suggested to use an ioctl changing f_ops.read. Userland
> would be like:
>
>> int fd = open("/mnt/btrfs");
>> ioctl(fd, BTRFS_IOC_STREAM);
>> while (...) {
>> 	read(fd, buf, 4096);
>> 	...
>> }
>> close(fd);
>
> To avoid doing buffering myself, I suggested passing a fd to the kernel
> where it is expected to dump the generated information, like:
>
>> int fd;
>> int pipefd[2];
>> struct io_args io_args;
>>
>> fd = open("/mnt/btrfs");
>> pipe(pipefd);
>> io_agrs.dest = pipefd[0];
>>
>> /* thread 1 */
>> ioctl(fd, BTRFS_IOC_STREAM,&io_args);
>> /* thread 2 */
>> while (...) {
>> 	read(pipefd[1], buf, 4096);
>> 	...
>> }
>
> Any opinions on those or different suggestions? Thanks,
> -Jan
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