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 >>>>>>>> >>>>>>> >>>>>> >>>>>> >>>>>> >>> >>> >>> >> > > >
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