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Re: [RFC] unifying write variants for filesystems

To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: [RFC] unifying write variants for filesystems
From: Zach Brown <zab@xxxxxxxxxx>
Date: Wed, 5 Feb 2014 12:42:03 -0800
Cc: Kent Overstreet <kmo@xxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Jens Axboe <axboe@xxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, linux-fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Sage Weil <sage@xxxxxxxxxxx>, Steve French <sfrench@xxxxxxxxx>, Anton Altaparmakov <anton@xxxxxxxxxx>, Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
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User-agent: Mutt/1.5.21 (2010-09-15)
> So what exactly does generic_segments_check() give us?  Is it just that
> everybody went "well, maybe there's some weird path where we don't do
> validation; let's leave it there"?  Linus?

Sounds likely.  I'd bet that the btrfs call was just copied from
__generic_file_aio_write() when btrfs grew its own .aio_write method:

11c65dccf70be9ace5dbd3906778e1a099b1fee1
Author: Josef Bacik <josef@xxxxxxxxxx>
Date:   Sun May 23 11:07:21 2010 -0400

    Btrfs: do aio_write instead of write

It probably amounts to no more than ocount = iov_length().

- z

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