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 >
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