Re: [RFC] odd thing in btrfs_file_aio_write()

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

-------- Original Message --------
Subject: Re: [RFC] odd thing in btrfs_file_aio_write()
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: 2014年04月14日 10:48
> On Mon, Apr 14, 2014 at 10:35:08AM +0800, Qu Wenruo wrote:
>> Oh, that's my fault, I forgot that iov can be chained.
>>
>> I should use 'pos + count' instead.
> BTW, will there be any difference if 10Mb write starts one byte before EOF?
This will not be a problem, since btrfs will not update the inode size 
until the data is written.
So this behavior will not cause empty gap.
> IOW, is that if (start_pos > i_size_read(inode)) { in there correct
> these days?  And what'll happen if we hit e.g. an unmapped page in the
> middle of the data being written?  That will result in short write, but
> will it truncate what's left of that dummy range?
I'm very sorry for my poor that I could not understand the question well.
Would you please explain what does the "unmapped page" means?

Did you mean two noncontinuous iovecs?
If you did mean that, it seems that I should expand the end_pos to the 
end of the iovec...

Thanks,
Qu