On Tue, Aug 4, 2020 at 5:40 PM James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, 2020-08-03 at 14:36 +0100, David Howells wrote: > > Here's a set of patches that adds a system call, fsinfo(), that > > allows information about the VFS, mount topology, superblock and > > files to be retrieved. > > > > The patchset is based on top of the notifications patchset and allows > > event counters implemented in the latter to be retrieved to allow > > overruns to be efficiently managed. > > Could I repeat the question I asked about six months back that never > got answered: > > https://lore.kernel.org/linux-api/1582316494.3376.45.camel@xxxxxxxxxxxxxxxxxxxxx/ > > It sort of petered out into a long winding thread about why not use > sysfs instead, which really doesn't look like a good idea to me. > > I'll repeat the information for those who want to quote it easily on > reply without having to use a web interface: > > --- > Could I make a suggestion about how this should be done in a way that > doesn't actually require the fsinfo syscall at all: it could just be > done with fsconfig. The idea is based on something I've wanted to do > for configfd but couldn't because otherwise it wouldn't substitute for > fsconfig, but Christian made me think it was actually essential to the > ability of the seccomp and other verifier tools in the critique of > configfd and I belive the same critique applies here. > > Instead of making fsconfig functionally configure ... as in you pass > the attribute name, type and parameters down into the fs specific > handler and the handler does a string match and then verifies the > parameters and then acts on them, make it table configured, so what > each fstype does is register a table of attributes which can be got and > optionally set (with each attribute having a get and optional set > function). We'd have multiple tables per fstype, so the generic VFS > can register a table of attributes it understands for every fstype > (things like name, uuid and the like) and then each fs type would > register a table of fs specific attributes following the same pattern. > The system would examine the fs specific table before the generic one, > allowing overrides. fsconfig would have the ability to both get and > set attributes, permitting retrieval as well as setting (which is how I > get rid of the fsinfo syscall), we'd have a global parameter, which > would retrieve the entire table by name and type so the whole thing is > introspectable because the upper layer knows a-priori all the > attributes which can be set for a given fs type and what type they are > (so we can make more of the parsing generic). Any attribute which > doesn't have a set routine would be read only and all attributes would > have to have a get routine meaning everything is queryable. fsconfig(2) takes an fd referring to an fs_context, that in turn refers to a super_block. So using fsconfig() for retrieving super_block attributes would be fine (modulo value being const, and lack of buffer size). But what about mount attributes? I don't buy the argument that an API needs to be designed around the requirements of seccomp and the like. It should be the other way round. In that, I think your configfd idea was fine, and would answer the above question. Thanks, Miklos
