linux-ext4 - Re: [PATCH] debugfs: Add inline data feature for symlink.

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Message-ID: <20140801164810.GT8628@birch.djwong.org>
Date:	Fri, 1 Aug 2014 09:48:10 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	侯普(谷熠) <houpu.hp@...baba-inc.com>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] debugfs: Add inline data feature for symlink.

On Fri, Aug 01, 2014 at 06:37:56PM +0800, 侯普(谷熠) wrote:
> On Thu, Jul 31, 2014 at 02:58:52PM +0800, Pu Hou wrote:
> >> Symlink in debugfs can take advantage of inline data feature. The path name of the target of the symbol link which is longer than 60 byte and shorter than 132 byte can stay in inline data area.
> >
> >I think Ted prefers wrapping commit messages at 70 bytes.
> >
> Thanks for reminding me. I will fix it.
> 
> >> +	data.ea_size = size - EXT4_MIN_INLINE_DATA_SIZE;
> >> +	data.ea_data = buf + EXT4_MIN_INLINE_DATA_SIZE;
> >> +	return ext2fs_inline_data_ea_set(&data);
> >
> >Doesn't ext2fs_inline_data_set() suffice?
> >
> It is unnecessary to use this dedicated function.

Why do you say it's unnecessary?  The dedicated function does (or at least is
supposed to) do exactly what you want.

Now I'm wondering -- why worry about size at all?  You can modify
ext2fs_symlink to call ext2fs_inline_data_set() directly.  If there's not
enough room, it'll return EXT2_ET_INLINE_DATA_NO_SPACE and you can try again
with the classic stuff-it-in-a-block method.

(Of course, if you try this and the API turns not to behave as advertised I'd
like to hear about that too. :))

--D

> 
> >> +					sizeof(__u32)+
> >> +					EXT4_MIN_INLINE_DATA_SIZE;
> >> +			inline_link = (target_len < max_inline);
> >
> >Does ext2fs_xattr_inode_max_size() + EXT4_MIN_INLINE_DATA_SIZE return incorrect
> >results?  I don't think we should have all xattr specific stuff belongs here in
> >the symlink routines.
> 
> Sorry. I did not notice that some xattr might be existed  when an inode
> number is passed to ext2fs_symlink(). But, as far as I can see, when 0
> is pass as inode number. ext2fs_xattr_inode_max_size() will read inode
> by ext2fs_read_inode_full(). But at that time, we have not writen the
> inode back. and the size of inline data for symlink is uncertain.
> I will try to find a workaround.
> 
> >> -		if (retval)
> >> -			goto cleanup;
> >> +		  retval = io_channel_write_blk64(fs->io, blk, 1, block_buf);
> >> +		  if (retval)
> >> +		    goto cleanup;
> >
> >Please fix the indentation inconsistency (tabs, not spaces).
> 
> >> -	if (!fastlink)
> >> +	if ((!fastlink) && (!inline_link))
> >
> >Probably unnecessary to put !fastlink and !inline_link in parentheses.
> >
> >--D
> Darrick, thank again for your generous help.
> --
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