Qu, Given inode, i get the fsid via: inode->i_sb->s_dev; this return dev_t and not u8/u16
On Sun, Jan 14, 2018 at 12:44 PM, Qu Wenruo <quwenruo.bt...@gmx.com> 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.bt...@gmx.com> 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 <ila...@gmail.com> wrote: >>>>> But both filesystems will have same fsid? >>>>> >>>>> On Jan 14, 2018 12:04, "Nikolay Borisov" <nbori...@suse.com> 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.bt...@gmx.com> >>>>>>> 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 majord...@vger.kernel.org >>>>>>>>> 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
