On Tue, Mar 26, 2019 at 09:50:28AM -0700, Daniel Colascione wrote: > On Tue, Mar 26, 2019 at 9:44 AM Christian Brauner <christian@xxxxxxxxxx> wrote: > > > > On Tue, Mar 26, 2019 at 09:38:31AM -0700, Daniel Colascione wrote: > > > On Tue, Mar 26, 2019 at 9:34 AM Christian Brauner <christian@xxxxxxxxxx> wrote: > > > > > > > > On Tue, Mar 26, 2019 at 05:31:42PM +0100, Christian Brauner wrote: > > > > > On Tue, Mar 26, 2019 at 05:23:37PM +0100, Christian Brauner wrote: > > > > > > On Tue, Mar 26, 2019 at 09:17:07AM -0700, Daniel Colascione wrote: > > > > > > > Thanks for the patch. > > > > > > > > > > > > > > On Tue, Mar 26, 2019 at 8:55 AM Christian Brauner <christian@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > The pidctl() syscalls builds on, extends, and improves translate_pid() [4]. > > > > > > > > I quote Konstantins original patchset first that has already been acked and > > > > > > > > picked up by Eric before and whose functionality is preserved in this > > > > > > > > syscall: > > > > > > > > > > > > > > We still haven't had a much-needed conversation about splitting this > > > > > > > system call into smaller logical operations. It's important that we > > > > > > > address this point before this patch is merged and becomes permanent > > > > > > > kernel ABI. > > > > > > > > > > > > I don't particularly mind splitting this into an additional syscall like > > > > > > e.g. pidfd_open() but then we have - and yes, I know you'll say > > > > > > syscalls are cheap - translate_pid(), and pidfd_open(). What I like > > > > > > about this rn is that it connects both apis in a single syscall > > > > > > and allows pidfd retrieval across pid namespaces. So I guess we'll see > > > > > > what other people think. > > > > > > > > > > There's something to be said for > > > > > > > > > > pidfd_open(pid_t pid, int pidfd, unsigned int flags); > > > > > > > > > > /* get pidfd */ > > > > > int pidfd = pidfd_open(1234, -1, 0); > > > > > > > > > > /* convert to procfd */ > > > > > int procfd = pidfd_open(-1, 4, 0); > > > > > > > > > > /* convert to pidfd */ > > > > > int pidfd = pidfd_open(4, -1, 0); > > > > > > > > probably rather: > > > > > > > > int pidfd = pidfd_open(-1, 4, PIDFD_TO_PROCFD); > > > > int procfd = pidfd_open(-1, 4, PROCFD_TO_PIDFD); > > > > int pidfd = pidfd_open(1234, -1, 0); > > > > > > These three operations look like three related but distinct functions > > > to me, and in the second case, the "pidfd_open" name is a bit of a > > > misnomer. IMHO, the presence of an "operation name" field in any API > > > is usually a good indication that we're looking at a family of related > > > APIs, not a single coherent operation. > > > > So I'm happy to accommodate the need for a clean api even though I > > disagree that what we have in pidctl() is unclean. > > But I will not start sending a pile of syscalls. There is nothing > > necessarily wrong to group related APIs together. > > In the email I sent just now, I identified several specific technical > disadvantages arising from unnecessary grouping of system calls. We > have historical evidence in the form of socketcall that this grouping > tends to be regrettable. I don't recall your identifying any > offsetting technical advantages. Did I miss something? > > > By these standards the > > new mount API would need to be like 30 different syscalls, same for > > keyring management. > > Can you please point out the problem that would arise from splitting > the mount and keyring APIs this way? One could have made the same > argument about grouping socket operations, and this socket-operation > grouping ended up being a mistake. The main reasons why I am not responding to such mails is that I don't want long tangents about very generic issues. If you can find support from people that prefer to split this into three separate syscalls: pidfd_open() pidfd_procfd() procfd_pidfd() I'm happy to do it this way. But it seems we can find a compromise, e.g. by having pidfd_open(pid_t pid, int fd, int fd, unsigned int flags) and avoid that whole email waterfall.
