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) >> > 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 ? >> >> 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
