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authorChristian Brauner <brauner@kernel.org>2024-02-12 16:00:50 +0100
committerChristian Brauner <brauner@kernel.org>2024-02-28 17:17:07 +0100
commit50f4f2d197e194ec0356962b99ca2b72e9a37bc8 (patch)
tree0ef32934c1468f6b1d8b2a7aadd8e7a776fa358b /fs/pidfs.c
parente1fb1dc08e73466830612bcf2f9f72180965c9ba (diff)
pidfd: move struct pidfd_fops
Move the pidfd file operations over to their own file in preparation of implementing pidfs and to isolate them from other mostly unrelated functionality in other files. Link: https://lore.kernel.org/r/20240213-vfs-pidfd_fs-v1-1-f863f58cfce1@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs/pidfs.c')
-rw-r--r--fs/pidfs.c122
1 files changed, 122 insertions, 0 deletions
diff --git a/fs/pidfs.c b/fs/pidfs.c
new file mode 100644
index 000000000000..eccb291862a0
--- /dev/null
+++ b/fs/pidfs.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/magic.h>
+#include <linux/mount.h>
+#include <linux/pid.h>
+#include <linux/pid_namespace.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/proc_ns.h>
+#include <linux/pseudo_fs.h>
+#include <linux/seq_file.h>
+#include <uapi/linux/pidfd.h>
+
+static int pidfd_release(struct inode *inode, struct file *file)
+{
+ struct pid *pid = file->private_data;
+
+ file->private_data = NULL;
+ put_pid(pid);
+ return 0;
+}
+
+#ifdef CONFIG_PROC_FS
+/**
+ * pidfd_show_fdinfo - print information about a pidfd
+ * @m: proc fdinfo file
+ * @f: file referencing a pidfd
+ *
+ * Pid:
+ * This function will print the pid that a given pidfd refers to in the
+ * pid namespace of the procfs instance.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its pid. This is
+ * similar to calling getppid() on a process whose parent is outside of
+ * its pid namespace.
+ *
+ * NSpid:
+ * If pid namespaces are supported then this function will also print
+ * the pid of a given pidfd refers to for all descendant pid namespaces
+ * starting from the current pid namespace of the instance, i.e. the
+ * Pid field and the first entry in the NSpid field will be identical.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its first NSpid
+ * entry and no others will be shown.
+ * Note that this differs from the Pid and NSpid fields in
+ * /proc/<pid>/status where Pid and NSpid are always shown relative to
+ * the pid namespace of the procfs instance. The difference becomes
+ * obvious when sending around a pidfd between pid namespaces from a
+ * different branch of the tree, i.e. where no ancestral relation is
+ * present between the pid namespaces:
+ * - create two new pid namespaces ns1 and ns2 in the initial pid
+ * namespace (also take care to create new mount namespaces in the
+ * new pid namespace and mount procfs)
+ * - create a process with a pidfd in ns1
+ * - send pidfd from ns1 to ns2
+ * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
+ * have exactly one entry, which is 0
+ */
+static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+ struct pid *pid = f->private_data;
+ struct pid_namespace *ns;
+ pid_t nr = -1;
+
+ if (likely(pid_has_task(pid, PIDTYPE_PID))) {
+ ns = proc_pid_ns(file_inode(m->file)->i_sb);
+ nr = pid_nr_ns(pid, ns);
+ }
+
+ seq_put_decimal_ll(m, "Pid:\t", nr);
+
+#ifdef CONFIG_PID_NS
+ seq_put_decimal_ll(m, "\nNSpid:\t", nr);
+ if (nr > 0) {
+ int i;
+
+ /* If nr is non-zero it means that 'pid' is valid and that
+ * ns, i.e. the pid namespace associated with the procfs
+ * instance, is in the pid namespace hierarchy of pid.
+ * Start at one below the already printed level.
+ */
+ for (i = ns->level + 1; i <= pid->level; i++)
+ seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
+ }
+#endif
+ seq_putc(m, '\n');
+}
+#endif
+
+/*
+ * Poll support for process exit notification.
+ */
+static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
+{
+ struct pid *pid = file->private_data;
+ bool thread = file->f_flags & PIDFD_THREAD;
+ struct task_struct *task;
+ __poll_t poll_flags = 0;
+
+ poll_wait(file, &pid->wait_pidfd, pts);
+ /*
+ * Depending on PIDFD_THREAD, inform pollers when the thread
+ * or the whole thread-group exits.
+ */
+ guard(rcu)();
+ task = pid_task(pid, PIDTYPE_PID);
+ if (!task)
+ poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
+ else if (task->exit_state && (thread || thread_group_empty(task)))
+ poll_flags = EPOLLIN | EPOLLRDNORM;
+
+ return poll_flags;
+}
+
+const struct file_operations pidfd_fops = {
+ .release = pidfd_release,
+ .poll = pidfd_poll,
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = pidfd_show_fdinfo,
+#endif
+};