On Mon, 2 Jun 2014 14:42:51 +0800 Zheng Liu <gnehzuil.liu@xxxxxxxxx> wrote: >Hi all, > >On Fri, May 30, 2014 at 04:26:33PM -0700, Darrick J. Wong wrote: >> On Tue, Feb 18, 2014 at 11:07:24AM -0800, Andreas Dilger wrote: >> > I suspect that the stats for symlinks > 60 but < ~150 chars is only a very >> > small fraction of files. If the code complexity of handling this is very >> > small (i.e. it is just handled as a natural consequence of writing "data" >> > of this size) then I would be OK with it. >> > >> > Otherwise, I expect the code and maintenance overhead of supporting >> > the 0.01% (?) of symlinks that are this size is probably lot worth it. >> > >> > People could check what the actual usage is via the "fsstats" tool at: >> > >> > http://www.pdsi-scidac.org/fsstats/ >> > >> > There is also data there already that reports stats on symlink length, but >> > it is mostly HPC filesystems and it might be better to redo this with a >> > desktop-type workload. >> >> I think we should either put in this kernel patch so that we can read inline >> data fast symlinks, or remove the ability to write inline data fast symlinks. >> It's a bit surprising that I can do: >> >> # mke2fs -t ext4 -O inline_data /dev/sdb >> # mount /dev/sdb /mnt/ >> # ln -s "Fuzzy Wuzzy was a bear. Fuzzy Wuzzy had no hair. I guess he wasn't >> fuzzy, was he?" /mnt/biglink # readlink /mnt/biglink >> Fuzzy Wuzzy was a bear. Fuzzy Wuzzy had no hair. I guess he wasn't fuzzy, >> was he? # umount /mnt >> # mount /dev/sdb /mnt/ >> # readlink /mnt/biglink >> Fuzzy Wuzzy was a bear. Fuzzy Wuzzy had no hair. I guess he >> >> What happened to the punchline of the limerick? ------------^^^^^^^ ???? :) > >Do *not* apply this patch, please. I revise this patch and I think it >is not right solution, although it can fix the bug. > >The root cause is in ext4_inode_is_fast_symlink() function that it >doesn't check whether or not an inode has inline data. After creating >a normal symlink, the symlink will be stored in ->i_block and extra >space if the length of symlink is greater than 60 bytes and less than >extra space in inline data. In the mean time, this inode has inline >data flag. If the file system is remounted, ext4_inode_is_fast_symlink >thinks this inode is a fast symlink, and the data in ->i_block is copied >to user. I will send a new patch to fix this bug. > >> >> e2fsck still seems to think that you can't have inline_data fast symlinks. I >> don't see a downside to continuing to allow them. > >Meanwhile another patch for e2fsck also will be sent out soon in order >to handle symlink properly with inline data in e2fsck. > >Regards, > - Zheng fsstats on root on my desktop, percentage of symlink targets 64 - 150 characters long is 22%, almost all in the 64-71 char bucket. Lots of them are theme icons and python packages, some shared library objects, nothing that many people won't have. --ian -- 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
