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 ?
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
