On Mon, Apr 25, 2011 at 08:44:13PM +0100, Daniel Drake wrote: > On 21 April 2011 05:46, James Cameron <[email protected]> wrote: > > Allows the unused filesystem blocks of the image to be left out of > > the .zd file, resulting in a factor of two reduction in fs-update > > times on a typical build on a 4GB microSD. ?Greater reduction occurs > > on larger microSD or SD cards. > > > > Has no effect if a fill pattern file is not found. > > A more correct option would be to use the FIEMAP ioctl to detect the > gaps in the file and determine the unused blocks that way. Have you > investigated this?
No, because that would fail to detect blocks that have been read and then written unchanged. While I don't know of any examples of that being done, it is still a possibility, either now or in the future. Using FIEMAP will place a kernel version dependency on zhashfs unnecessarily, since the task can be done with memcmp. It would also be more complex code to process the FIEMAP extents; more complex than memcmp. It would also require the output directory to be on a filesystem that supports sparse files. (Attempting to create a sparse file using dd on a FAT filesystem results in a non-sparse file of the specified size ... a FIEMAP ioctl on this would show no holes). -- James Cameron http://quozl.linux.org.au/ _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
