Qu, Thank you very much for detailed response. I would like to understand something, on VFS, it is guaranteed that in a given filesystem, only 1 inode number will be used, it is unique. In btrfs, you say the inode uniqueness is per volume, each volume has its own inode space, How is it possible ? Thats why when I execute "stat /somepath/file" I receive fsid that looks like "36h/54d" but from kernel code, If I examine struct fs_info->fsid i get 52. I call this Physical/Virtual, physical is the real id - 52, and virtual is 36h/54d, because this what btrfs implementation returns.. from where is that property taken ? The inode number inode->i_ino is the same from both userspace (stat ...) and kernel code. If on the same filesystem (52), you say, same inode number can be used, as long as they are on different volumes - Is it possible ? Doesn't it break the VFS inode uniqueness ? Is there also a virtual/physical inode numbers ? and if so, is it possible to get from kernel structure ? because inode->i_ino always return what stat returns.. unlike fsid as i wrote above. Thanks !! On Sun, Jan 14, 2018 at 12:44 PM, Qu Wenruo <quwenruo.btrfs@xxxxxxx> wrote: > > > On 2018年01月14日 18:32, Ilan Schwarts wrote: >> Thank you for clarification. >> Just 2 quick questions, >> 1. Sub volumes - 2 sub volumes cannot have 2 same inode numbers ? > > They can. > > So to really locate an inode in btrfs, you need: > > fsid (locate the fs) -> subvolume id (locate subvolume) -> inode number. > > fsid can be feteched from superblock as mentioned in previous reply. > > subvolume id can be get from BTRFS_I(inode)->root. > And normally root is what you need. > > If you really want the number, then either > BTRFS_I(inode)->root->objectid or > BTRFS_I(inode)->root->root_key->objectid will give you the u64 subvolume id. > >> 2. Why fsInfo fsid return u8 and the traditional file system return >> dev_t, usually 32 integer ? > > As far as I found in xfs or ext4, their fsid is still u8[16] or uuid_t, > same as btrfs. > > For ext4 it's ext4_super_block->s_uuid[16] > And for xfs, it's xfs_sb->sb_uuid. > > I don't know how you get the dev_t parameter. > > Thanks, > Qu > >> >> >> On Sun, Jan 14, 2018 at 12:22 PM, Qu Wenruo <quwenruo.btrfs@xxxxxxx> wrote: >>> >>> >>> On 2018年01月14日 18:13, Ilan Schwarts wrote: >>>> both btrfs filesystems will have same fsid ? >>>> >>>> >>>> On Sun, Jan 14, 2018 at 12:06 PM, Ilan Schwarts <ilan84@xxxxxxxxx> wrote: >>>>> But both filesystems will have same fsid? >>>>> >>>>> On Jan 14, 2018 12:04, "Nikolay Borisov" <nborisov@xxxxxxxx> wrote: >>>>>> >>>>>> >>>>>> >>>>>> On 14.01.2018 12:02, Ilan Schwarts wrote: >>>>>>> First of all, Thanks for response ! >>>>>>> So if i have 2 btrfs file system on the same machine (not your >>>>>>> everyday scenario, i know) >>> >>> Not a problem, the 2 filesystems will have 2 different fsid. >>> >>> (And it's my everyday scenario, since fstests neeeds TEST_DEV and >>> SCRATCH_DEV_POOL) >>> >>>>>>> Lets say a file is created on device A, the file gets inode number X >>>>>>> is it possible on device B to have inode number X also ? >>>>>>> or each device has its own Inode number range ? >>> >>> Forget the mess about device. >>> >>> Inode is bounded to a filesystem, not bounded to a device. >>> >>> Just traditional filesytems are normally bounded to a single device. >>> (Although even traditional filesystems can have external journal devices) >>> >>> So there is nothing to do with device at all. >>> >>> And you can have same inode numbers in different filesystems, but >>> BTRFS_I(inode)->root->fs_info will point to different fs_infos, with >>> different fsid. >>> >>> So return to your initial question: >>>> both btrfs filesystems will have same fsid ? >>> >>> No, different filesystems will have different fsid. >>> >>> (Unless you're SUUUUUUUUUUUUUUUUUUUPER lucky to have 2 filesystems with >>> same fsid) >>> >>> Thanks, >>> Qu >>> >>> >>>>>> >>>>>> Of course it is possible. Inodes are guaranteed to be unique only across >>>>>> filesystem instances. In your case you are going to have 2 fs instances. >>>>>> >>>>>>> >>>>>>> I need to create unique identifier for a file, I need to understand if >>>>>>> the identifier would be: GlobalFSID_DeviceID_Inode or DeviceID_Inode >>>>>>> is enough. >>>>>>> >>>>>>> Thanks >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Sun, Jan 14, 2018 at 11:13 AM, Qu Wenruo <quwenruo.btrfs@xxxxxxx> >>>>>>> wrote: >>>>>>>> >>>>>>>> >>>>>>>> On 2018年01月14日 16:33, Ilan Schwarts wrote: >>>>>>>>> Hello btrfs developers/users, >>>>>>>>> >>>>>>>>> I was wondering regarding to fetching the correct fsid on btrfs from >>>>>>>>> the context of a kernel module. >>>>>>>> >>>>>>>> There are two IDs for btrfs. (in fact more, but you properly won't need >>>>>>>> the extra ids) >>>>>>>> >>>>>>>> FSID: Global one, one fs one FSID. >>>>>>>> Device ID: Bonded to device, each device will have one. >>>>>>>> >>>>>>>> So in case of 2 devices btrfs, each device will has its own device id, >>>>>>>> while both of the devices have the same fsid. >>>>>>>> >>>>>>>> And I think you're talking about the global fsid instead of device id. >>>>>>>> >>>>>>>>> if on suse11.3 kernel 3.0.101-0.47.71-default in order to get fsid, I >>>>>>>>> do the following: >>>>>>>>> convert inode struct to btrfs_inode struct (use btrfsInode = >>>>>>>>> BTRFS_I(inode)), then from btrfs_inode struct i go to root field, and >>>>>>>>> from root i take anon_dev or anon_super.s_dev. >>>>>>>>> struct btrfs_inode *btrfsInode; >>>>>>>>> btrfsInode = BTRFS_I(inode); >>>>>>>>> btrfsInode->root->anon_super.s_dev or >>>>>>>>> btrfsInode->root->anon_dev - depend on kernel. >>>>>>>> >>>>>>>> The most directly method would be: >>>>>>>> >>>>>>>> btrfs_inode->root->fs_info->fsid. >>>>>>>> (For newer kernel, as I'm not familiar with older kernels) >>>>>>>> >>>>>>>> Or from superblock: >>>>>>>> btrfs_inode->root->fs_info->super_copy->fsid. >>>>>>>> (The most reliable one, no matter which kernel version you're using, as >>>>>>>> long as the super block format didn't change) >>>>>>>> >>>>>>>> For device id, it's not that commonly used unless you're dealing with >>>>>>>> chunk mapping, so I'm assuming you're referring to fsid. >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Qu >>>>>>>> >>>>>>>>> >>>>>>>>> In kernel 3.12.28-4-default in order to get the fsid, i need to go >>>>>>>>> to the inode -> superblock -> device id (inode->i_sb->s_dev) >>>>>>>>> >>>>>>>>> Why is this ? and is there a proper/an official way to get it ? >>>>>>>>> -- >>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" >>>>>>>>> in >>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>>>>>>> >>>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>> >>>> >>>> >>> >> >> >> > -- - Ilan Schwarts -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
