linux-ext4 - Re: debugfs: dump a sparse file as a new sparse file

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Date:	Tue, 1 Jan 2013 20:33:44 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	George Spelvin <linux@...izon.com>, linux-ext4@...r.kernel.org
Subject: Re: debugfs: dump a sparse file as a new sparse file

On Mon, Dec 31, 2012 at 09:08:41PM -0500, Theodore Ts'o wrote:
> On Thu, Nov 15, 2012 at 04:46:13AM -0000, Zheng Liu wrote:
> > --- a/debugfs/dump.c
> > +++ b/debugfs/dump.c
> > @@ -105,10 +105,11 @@ static void dump_file(const char *cmdname, ext2_ino_t ino, int fd,
> >  {
> >  	errcode_t retval;
> >  	struct ext2_inode	inode;
> > -	char 		buf[8192];
> > +	char 		buf[current_fs->blocksize];
> 
> Note: this is a non-standard/non-portable GCC extension.  The best way
> to fix this is to explicitly malloc the buffer and then free it before
> dump_file exits.
> 
> Also, fixing the hard-coded maximum 8k block size, so these sorts of
> changes should be done in a separate commit.
> 
> >  extern errcode_t ext2fs_file_llseek(ext2_file_t file, __u64 offset,
> > diff --git a/lib/ext2fs/fileio.c b/lib/ext2fs/fileio.c
> > index 1f7002c..d25ebb4 100644
> > --- a/lib/ext2fs/fileio.c
> > +++ b/lib/ext2fs/fileio.c
> > @@ -176,23 +176,26 @@ static errcode_t sync_buffer_position(ext2_file_t file)
> >   * This function loads the file's block buffer with valid data from
> >   * the disk as necessary.
> >   *
> > - * If dontfill is true, then skip initializing the buffer since we're
> > + * If flags is true, then skip initializing the buffer since we're
> >   * going to be replacing its entire contents anyway.  If set, then the
> >   * function basically only sets file->physblock and EXT2_FILE_BUF_VALID
> >   */
> >  #define DONTFILL 1
> 
> The comment "If flags is true..." should be changed to "if the
> DONTFILL flag is set..."  
> 
> @@ -202,7 +205,11 @@ static errcode_t load_buffer(ext2_file_t file, int dontfill)
>  			} else
>  				memset(file->buf, 0, fs->blocksize);
>  		}
> -		file->flags |= EXT2_FILE_BUF_VALID;
> +		if (flags == SEEK && ((ret_flags & BMAP_RET_UNINIT) ||
> +		    file->physblock == 0))
> +			valid = 0;
> +		if (valid)
> +			file->flags |= EXT2_FILE_BUF_VALID;
> 
> 
> valid is initialized to 1, and then set to zero above.  So I'm not
> sure what the point is having the valid variable.  Why not do
> something like this:
> 
> 		if (!(flags == SEEK && ((ret_flags & BMAP_RET_UNINIT) ||
> 				      file->physblock == 0)))
> 			file->flags |= EXT2_FILE_BUF_VALID;
> 
> or...
> 		if (((flags != SEEK) ||
> 		     (!(ret_flags & BMAP_RET_UNINIT) && file->physblock)))
> 			file->flags |= EXT2_FILE_BUF_VALID;
> 
> 
> Also, can you add a definition of what SEEK actually means in the
> context of load_buffer()?

Hi Ted,

I have sent the latest patch series out.  Could you please review it?
Thanks for your time.

Regards,
                                                - Zheng
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