Hello. Phillip Lougher wrote: > Most filesystems will not create a sparse file if zero-byte filled > blocks are written. To create a sparse file you normally have to seek > beyond the file end and then write blocks, leaving a hole in-between the > positions. > > The information from stat can tell you if a file has been stored > sparsely, because the blocks used count will be less than the file size > suggests. > Then, I can use "dd if=/dev/zero" without worrying sparse files. Phillip Lougher wrote: > You don't mention what you're using to compress the ext3 image file. If > you're using Squashfs then it's much better to zero-fill the blocks > rather than use 255, because Squashfs detects zero-filled blocks and > stores them sparsely. This not only gets slightly better compression > (than a compressed zero-filled block), but reading is also slightly faster. > Yes, I use squashfs. What I wanted to do is "Zero-clearing *all zero-clearable* bytes". Suppose blocks for inode are 8192 bytes and only 128 bytes are in use, I think there are 8064 bytes I can zero-fill. Suppose blocks for file data are 8192 bytes and a file's size is 1 byte, I think there are 8191 bytes I can zero-fill. Such bytes may have non-zero values because directory entries can be unlink()ed and file data can be truncate()d. I wished there is a utility to zero-fill such bytes. Thanks a lot. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
