On Sat, Mar 17, 2018 at 7:40 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Fri, Mar 16, 2018 at 11:24 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: >> On Fri, Mar 16, 2018 at 04:05:22PM +0200, Amir Goldstein wrote: >>> Hi guys, >>> >>> I am trying to get a lower bound for unused inode number MSB on >>> a mounted xfs super block, so I can publish it on struct super_block. >> >> Sorry, what? >> >> The inode number is owned by the filesystem - nobody should be >> touching it or making assumptions they can screw with it in any way. >> Let me clarify with the simplest example: With overlay of 2 layers, lower and upper on 2 different xfs fs assuming that stat(2) from xfs will not be using the 63 MSB: On stat(2) of an overlay upper inode we want to return: st_dev = <overlay anon bdev> st_ino = <real upper st_ino> On stat(2) of an overlay lower inode we want to return: st_dev = <overlay anon bdev> st_ino = <real lower st_ino> | 1 << 63 Now for ext4 this is always safe to do and we find that automatically due to the fact that ext4 uses the default encode_fh generic 32bit inode encoding. For xfs this should also be safe, but we don't want to whitelist xfs by name/magic, so we want xfs to publish the max amount of bits exposed to user with stat(2)/getdents(3). Recently, I became aware of an nfsd use case that also looks at inode->i_ino, so we may want to also be able to assume max_ino_bits also applies to inode->i_ino, but if you tell us to stay clear of inode->i_ino, then we can always use stat.st_ino. Thanks, Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
