From: Zheng Liu <gnehzuil.liu@gmail.com>
To: Theodore Ts'o <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org, George Spelvin <linux@horizon.com>,
Zheng Liu <wenqing.lz@taobao.com>
Subject: Re: [PATCH 2/2 v2] debugfs: dump a sparse file as a new sparse file
Date: Fri, 4 Jan 2013 12:05:05 +0800 [thread overview]
Message-ID: <20130104040505.GA27833@gmail.com> (raw)
In-Reply-To: <20130101203858.GB12554@thunk.org>
On Tue, Jan 01, 2013 at 03:38:58PM -0500, Theodore Ts'o wrote:
> On Tue, Jan 01, 2013 at 08:30:15PM +0800, Zheng Liu wrote:
> > +errcode_t ext2fs_file_read2(ext2_file_t file, void *buf,
> > + unsigned int wanted, unsigned int *got,
> > + ext2_off64_t *seek)
>
> I'm a bit concenred about this abstraction. Consider what happens if
> wanted is greater than a block size --- for example, consider if
> wanted is 16k, and every other 1k block is uninitialized.
Hi Ted,
I wonder why wanted is 16k. If a program calls ext2fs_file_read()
function, seek will be 0 and SEEK flag won't be marked. The behavior of
ext2fs_file_read() is the same as before. If ext2fs_file_read2() is
called by dump_file(), seek won't be 0 and wanted is always equal to
block size. That is why I fix the hard-coded buffer length in dump_file().
If I miss something, please let me know.
Thanks,
- Zheng
>
> Then ext2fs_file_read2() will return *got set to 8k, and *seek set to
> 8k, and the buffer will contain the blocks that are initialized packed
> up right against each other.
>
> Worse, ext2fs_file_read() will do the same thing, so this commit
> changes how ext2fs_file_read() functions, and a program which expects
> to get the correct contents from the file will malfunction.
next prev parent reply other threads:[~2013-01-04 3:51 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-01 12:30 [PATCH 0/2 v2] debugfs: dump a sparse file as a new sparse file Zheng Liu
2013-01-01 12:30 ` [PATCH 1/2 v2] debugfs: fixup the hard-coded buffer length in dump_file Zheng Liu
2013-01-01 20:14 ` Theodore Ts'o
2013-01-01 12:30 ` [PATCH 2/2 v2] debugfs: dump a sparse file as a new sparse file Zheng Liu
2013-01-01 20:38 ` Theodore Ts'o
2013-01-04 4:05 ` Zheng Liu [this message]
2013-01-04 19:37 ` Theodore Ts'o
2013-01-05 4:45 ` Zheng Liu
2013-01-09 14:58 ` Theodore Ts'o
2013-01-09 15:34 ` Zheng Liu
2013-01-10 0:42 ` George Spelvin
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