linux-ext4 - Re: [PATCH] libext2fs: do not print any error message from libext2fs

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Date:	Tue, 21 May 2013 11:11:44 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH] libext2fs: do not print any error message from libext2fs

On Mon, May 20, 2013 at 10:36:36PM -0400, Theodore Ts'o wrote:
> On Sat, Apr 27, 2013 at 06:44:41PM +0800, Zheng Liu wrote:
> > diff --git a/debugfs/htree.c b/debugfs/htree.c
> > index ca39b4b..e042fd7 100644
> > --- a/debugfs/htree.c
> > +++ b/debugfs/htree.c
> > @@ -388,8 +388,11 @@ void do_dirsearch(int argc, char *argv[])
> >  	pb.len = strlen(pb.search_name);
> >  
> >  	if (ext2fs_inode_has_inline_data(current_fs, inode)) {
> > -		ext2fs_inline_data_dirsearch(current_fs, inode,
> > +		errcode_t retval;
> > +		retval = ext2fs_inline_data_dirsearch(current_fs, inode,
> >  					     argv[2], strlen(argv[2]));
> > +		if (retval)
> > +			printf("Entry found at inline data\n");
> >  		goto out;
> >  	}
> 
> The problem with this is that ext2_inline_data_dirsearch() also
> returns a non-zero error code.  So it returns 0 if the entry is not
> found in the inline data, 1 if it is found in the inline data, and
> some other error code --- and if some system call returns EPERM (which
> is one) there will be a collision.
> 
> This is an example of a badly designed library interface; and since I
> don't want to break backwards compatibility by removing a library
> interface once we've added one, we need to be very careful for each
> new interface that we are thinking of adding.
> 
> In this particular case, it's not clear to me that this library
> interface is at all useful, or that dirsearch needs to support inline
> directories at all in the first place.  The only reason dirsearch
> exists is to debug very large htree directories where the index has
> gotten corrupted.  For a small inline directory, it's just as easy to
> check to see what's in the directory by using the "ls" command.
> 
> So having dirsearch simply give an error and not support inline data
> directory, or to have dirsearch work by iterating over each of the
> entries in the inline data directory would both be acceptable
> alternatives.
> 
> And we need to carry out a similar very careful examination of all of
> the other new interfaces added to inline_data.c.  Sometimes it helps
> to document exactly what it is that this interface is doing, and what
> does it return under what circumstance.  Then think about what the
> best generic interface would be for all possible future users of that
> interface, not just the one or ones in the current e2fsprogs tree.
> And if there is only one caller of a particular interface, then it may
> be fair to ask the question whether it should be in the library at
> all.

Thanks for teaching me.  I will revise all new interfaces in
inline_data.c, and re-think about whether they really need to be added
or not.  If there are other things that I missed, please let me know.

Thanks,
                                                - Zheng
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