Messages in this thread | | | From | Jann Horn <> | Date | Wed, 27 Mar 2019 18:07:54 +0100 | Subject | Re: [PATCH 2/4] pid: add pidfd_open() |
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On Wed, Mar 27, 2019 at 5:22 PM Christian Brauner <christian@brauner.io> wrote: > pidfd_open() allows to retrieve pidfds for processes and removes the > dependency of pidfd on procfs. Multiple people have expressed a desire to > do this even when pidfd_send_signal() was merged. It is even recorded in [...] > IF PROCFD_TO_PIDFD is passed as a flag together with a file descriptor to a > /proc mount in a given pid namespace and a pidfd pidfd_open() will return a > file descriptor to the corresponding /proc/<pid> directory in procfs > mounts' pid namespace. pidfd_open() is very careful to verify that the pid
nit: s/mounts'/mount's/
> hasn't been recycled in between. > IF PIDFD_TO_PROCFD is passed as a flag together with a file descriptor > referencing a /proc/<pid> directory a pidfd referencing the struct pid > stashed in /proc/<pid> of the process will be returned.
nit: s/of the process //?
> The pidfd_open() syscalls in that manner resembles openat() as it uses a
nit: s/syscalls/syscall/
[...] > diff --git a/kernel/pid.c b/kernel/pid.c > index 20881598bdfa..c9e24e726aba 100644 > --- a/kernel/pid.c > +++ b/kernel/pid.c [...] > +static struct file *pidfd_open_proc_pid(const struct file *procf, pid_t pid, > + const struct pid *pidfd_pid) > +{ > + char name[11]; /* int to strlen + \0 */
nit: The comment is a bit off; an unconstrained int needs 1+10+1 bytes, I think? minus sign, 10 digits, nullbyte? But of course that can't actually happen here.
> + struct file *file; > + struct pid *proc_pid; > + > + snprintf(name, sizeof(name), "%d", pid); > + file = file_open_root(procf->f_path.dentry, procf->f_path.mnt, name, > + O_DIRECTORY | O_NOFOLLOW, 0);
Maybe explicitly write the implied O_RDONLY (which is 0) here for clarity?
[...] > +static int pidfd_to_procfd(pid_t pid, int procfd, int pidfd) > +{ > + long fd; > + pid_t ns_pid; > + struct fd fdproc, fdpid; > + struct file *file = NULL; > + struct pid *pidfd_pid = NULL; > + struct pid_namespace *proc_pid_ns = NULL; > + > + fdproc = fdget(procfd); > + if (!fdproc.file) > + return -EBADF; > + > + fdpid = fdget(pidfd); > + if (!fdpid.file) { > + fdput(fdpid);
Typo: s/fdput(fdpid)/fdput(fdproc)/
[...] > +SYSCALL_DEFINE4(pidfd_open, pid_t, pid, int, procfd, int, pidfd, unsigned int, > + flags) [...] > + if (!flags) { [...] > + rcu_read_lock(); > + pidfd_pid = get_pid(find_pid_ns(pid, task_active_pid_ns(current))); > + rcu_read_unlock();
The previous three lines are equivalent to `pidfd_pid = find_get_pid(pid)`.
> + fd = pidfd_create_fd(pidfd_pid, O_CLOEXEC);
Nit: You could hardcode O_CLOEXEC in pidfd_create_fd() and get rid of the second function argument if you want to.
> + put_pid(pidfd_pid); > + } else if (flags & PIDFD_TO_PROCFD) { [...] > + fd = pidfd_to_procfd(pid, procfd, pidfd);
The `pid` argument of pidfd_to_procfd() looks unused, maybe it makes sense to get rid of that?
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