Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > Umm... What's so special about cell/volume/domain/realm? Nothing particularly. But they're something various network filesystems might find useful. cell for AFS, domain for CIFS, realm for things that use kerberos. volume_id/uuid/name would be usable by ext4 too, for example. > And what do we do when a random filesystem gets added - should its > parameters go into catch-all pile (attr_parameter), FSINFO_ATTR_PARAMETER is a way to enumerate the configuration parameters passed to mount, as an alternative to parsing /proc/mounts. So, for example, afs has: enum afs_param { Opt_autocell, Opt_dyn, Opt_source, nr__afs_params }; static const struct fs_parameter_spec afs_param_specs[nr__afs_params] = { [Opt_autocell] = { fs_param_takes_no_value }, [Opt_dyn] = { fs_param_takes_no_value }, [Opt_source] = { fs_param_is_string }, }; static const struct constant_table afs_param_keys[] = { { "autocell", Opt_autocell }, { "dyn", Opt_dyn }, { "source", Opt_source }, }; My thought is that calling fsinfo(..., "/some/afs/file", ¶ms, ...) with: struct fsinfo_params params = { .request = FSINFO_ATTR_PARAMETER, .Nth = <parameter-number>, }; would get you back, for example: Nth Result ======= ========================================== 0 "autocell" (or "" if not set) 1 "dyn" (or "" if not set) 2 "source=%#grand.central.org:root.cell." 3+ -ENODATA (ie. there are no more) where Nth corresponds to the parameter specified by FSINFO_ATTR_PARAM_DESCRIPTION and Nth. Now for some filesystems, cgroups-v1 for example, there are parameters beyond the list (the subsystem name) and these can be listed after the predefined parameters, eg.: Nth Result ======= ========================================== 0 "all" or "" 1 "clone_children" or "" 2 "cpuset_v2_mode" or "" 3 "name" or "" 4 "none" or "" 5 "noprefix" or "" 6 "release_agent" or "" 7 "xattr" or "" 8 "<subsys0>" or "" 9 "<subsys1>" or "" 10 "<subsys2>" or "" ... -ENODATA > or should they get classes of their own? Yes. > For Cthulhu sake, who's going to maintain that enum in face of > random out-of-tree filesystems, each wanting a class or two its own? They don't get their own numbers unless they're in-tree. Full stop. We have the same issue with system calls and not-yet-upstream new syscalls. Note that, as I have the code now, the "type" of return value for each attribute must also be declared to the fsinfo() core, and the fsinfo core does the copy to/from userspace. > We'd tried that with device numbers; ask hpa how well has that > worked and how much did he love the whole experience... What would you do instead? I would prefer to avoid using text strings as keys because then I need a big lookup table, and possibly this gets devolved to each filesystem to handle - which ends up even more of a mess because then there's nothing to hold consistency. David