Thanks for detailed information ! Its a legacy code for kernel module i maintain.. dont talk to me about ancient when i need to maintain it to systems like solaris 8 or RHEL4 2.6.9 :(
On Mon, Jan 15, 2018 at 12:01 PM, Qu Wenruo <quwenruo.bt...@gmx.com> wrote: > > > On 2018年01月15日 17:24, Ilan Schwarts wrote: >> Qu, >> Given inode, i get the fsid via: inode->i_sb->s_dev; >> this return dev_t and not u8/u16 > > That's just a device number. > > Not really useful in btrfs, since btrfs is a multi-device filesystem. > > Thanks, > Qu > >> >> >> 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
