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.btrfs@xxxxxxx> 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 majordomo@xxxxxxxxxxxxxxx >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
