On Thu, Jul 28, 2011 at 09:56:15AM -0700, Darrick J. Wong wrote: > > the block. There of course is no reason to put an extent tail inside the > > inode itself. > > Does anybody have any objection to using crc32c (which we can hardware > accelerate on new Intel boxen) over crc16? I think it'll be pretty easy to use We use ethernet crc32 in ocfs2. btrfs uses crc32c. Frankly, I could have used crc32c if I'd really thought about the hardware acceleration benefits. I think it's a good idea for ext4. > some of the reserved space in the group descriptor to store checksums of the > block and inode bitmaps. Adding tails to the extent tree blocks seems a bit > trickier than that, but not a big deal, though I guess I'll have to reshuffle > the extent tree to free up space at the end of the block. > > I was also wondering what people think of adding checksums to directory files? > I think that it's possible to put a checksum in each directory block -- for > blocks containing a linear array of actual directory entries, we could zero out > the space past the end of the array and put a checksum at the very end of the > block. For the dx_node/dx_root blocks, we could probably use the space > occupied by the last dx_entry to store the checksum. Obviously, we'd have to > move whatever's at the end of the block elsewhere, but then, we have to do that > for the extent tree too. Basically, the last 4 bytes become the checksum after > whatever's occupying the space is relocated. :) ocfs2 adds trailer entries to every dirblock for the checksum. We also do our dirindex free list there. Since ocfs2 dirblocks are ext3 dirblocks, I bet you can rip off a lot of that code, including the feature compatibility stuff. See ocfs2_fs.h. > It looks like there's sufficient unused space in ext4_xattr_header to add a > checksum. > > Also -- should I create separate rocompat feature flags for each metadata > object that I add checksums to? Or just have one flag that covers them all? I really think you should checksum every metadata block. A few things will take some effort to shoehorn it in, but it is worth it. Joel -- Life's Little Instruction Book #173 "Be kinder than necessary." http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
