On Tue, Oct 18, 2016 at 9:41 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > On Fri, Sep 16, 2016 at 3:19 PM, Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote: >> The problem with writecount is: we want consistent handling of it for >> underlying filesystems as well as overlayfs. Making sure i_writecount is >> correct on all layers is difficult. Instead this patch makes sure that >> when write access is acquired, it's always done on the underlying writable >> layer (called the upper layer). We must also make sure to look at the >> writecount on this layer when checking for conflicting leases. >> >> Open for write already updates the upper layer's writecount. Leaving only >> truncate. >> >> For truncate copy up must happen before get_write_access() so that the >> writecount is updated on the upper layer. Problem with this is if >> something fails after that, then copy-up was done needlessly. E.g. if >> break_lease() was interrupted. Probably not a big deal in practice. >> >> Another interesting case is if there's a denywrite on a lower file that is >> then opened for write or truncated. With this patch these will succeed, >> which is somewhat counterintuitive. But I think it's still acceptable, >> considering that the copy-up does actually create a different file, so the >> old, denywrite mapping won't be touched. > > Miklos, > I think this breaks xfstest overlay/013 on v4.8, because execve() does > deny write on lower inode and then truncate happens on upper inode. It does break the xfstest, but as explained in the patch it shouldn't be a problem in practice. I think the test should just be fixed. Thanks, Miklos -- 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
