Thank you for clarification. Just 2 quick questions, 1. Sub volumes - 2 sub volumes cannot have 2 same inode numbers ? 2. Why fsInfo fsid return u8 and the traditional file system return dev_t, usually 32 integer ?
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
