bug#6131: [PATCH]: fiemap support for efficient sparse file copy (original) (raw)

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From: Paul Eggert
Subject: bug#6131: [PATCH]: fiemap support for efficient sparse file copy
Date: Tue, 15 Jun 2010 14:09:22 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.9) Gecko/20100423 Thunderbird/3.0.4

On 06/11/2010 01:31 AM, jeff.liu wrote:

+ fiemap->fmflags = FIEMAPFLAGSYNC;

If I'm reading the Linux source code correctly, this forces all the dirty blocks in the input file to disk, and forces the kernel to wait until all those blocks actually hit the disk. We don't need that; there shouldn't be a need to force any blocks to hit the disk. All that 'cp' needs to know is: please tell me the next block which might contain nonzero data. Is there some way that we can get that information without forcing the input file's blocks to disk?